Language resource management -- Feature structures

ISO 24610-1:2006 provides a format for the representation, storage and exchange of feature structures in natural language applications concerned with the annotation, production or analysis of linguistic data. It also defines a computer format for the description of constraints that bear on a set of features, feature values, feature specifications and operations on feature structures, thus offering a means of checking the conformance of each feature structure with regards to a reference specification.

Gestion des ressources linguistiques -- Structures de traits

Upravljanje z jezikovnimi viri - Strukture lastnosti - 1. del: Predstavitev struktur lastnosti

Strukture lastnosti so ključni sestavni del številnih jezikovnih formalizmov in osnovni mehanizmi za predstavitev informacij, ki jih predelajo ali oblikujejo aplikacije za jezikovno inženirstvo, ali ki so oblikovane za te aplikacije. Ta del standarda ISO 24610 zagotavlja format za predstavitev, shranjevanje in izmenjavo struktur lastnosti v aplikacijah za naravni jezik, ki označujejo, ustvarjajo ali analizirajo jezikovne podatke. Prav tako določa računalniški format za opis omejitev, ki veljajo za sklop lastnosti, vrednosti lastnosti, specifikacij lastnosti in operacij na strukturah lastnosti, in tako nudi način za preverjanje skladnosti vsake strukture lastnosti glede na referenčno specifikacijo.

General Information

Status
Published
Publication Date
09-Apr-2006
Current Stage
9020 - International Standard under periodical review
Start Date
15-Jul-2021

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SLOVENSKI STANDARD
SIST ISO 24610-1:2013
01-julij-2013

Upravljanje z jezikovnimi viri - Strukture lastnosti - 1. del: Predstavitev struktur

lastnosti
Language resource management -- Feature structures -- Part 1: Feature structure
representation

Gestion des ressources linguistiques -- Structures de traits -- Partie 1: Représentation de

structures de traits
Ta slovenski standard je istoveten z: ISO 24610-1:2006
ICS:
01.020 Terminologija (načela in Terminology (principles and
koordinacija) coordination)
01.140.20 Informacijske vede Information sciences
35.240.30 Uporabniške rešitve IT v IT applications in information,
informatiki, dokumentiranju in documentation and
založništvu publishing
SIST ISO 24610-1:2013 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO 24610-1:2013
---------------------- Page: 2 ----------------------
SIST ISO 24610-1:2013
INTERNATIONAL ISO
STANDARD 24610-1
FIrst edition
2006-04-15
Language resource management —
Feature structures —
Part 1:
Feature structure representation
Gestion des ressources linguistiques — Structures de traits —
Partie 1: Représentation de structures de traits
Reference number
ISO 24610-1:2006(E)
ISO 2006
---------------------- Page: 3 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but

shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In

the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

© ISO 2006

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2006 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
Contents Page

Foreword............................................................................................................................................................. v

Introduction ....................................................................................................................................................... vi

1 Scope..................................................................................................................................................... 1

2 Normative references........................................................................................................................... 1

3 Terms and definitions........................................................................................................................... 1

4 General characteristics of feature structure...................................................................................... 4

4.1 Overview................................................................................................................................................ 4

4.2 Use of feature structures ..................................................................................................................... 4

4.3 Basic concepts...................................................................................................................................... 5

4.4 Notations ............................................................................................................................................... 5

4.4.1 Overview................................................................................................................................................ 5

4.4.2 Graph notation ...................................................................................................................................... 6

4.4.3 Matrix notation ...................................................................................................................................... 7

4.4.4 XML-based notation.............................................................................................................................. 8

4.5 Structure sharing................................................................................................................................ 10

4.6 Collections as complex feature values............................................................................................. 12

4.6.1 Overview.............................................................................................................................................. 12

4.6.2 Lists as feature values ....................................................................................................................... 12

4.6.3 Sets as feature values ........................................................................................................................ 14

4.6.4 Multisets as feature values ................................................................................................................ 15

4.7 Typed feature structure...................................................................................................................... 16

4.7.1 Overview.............................................................................................................................................. 16

4.7.2 Types.................................................................................................................................................... 16

4.7.3 Notations ............................................................................................................................................. 16

4.8 Subsumption: relation on feature structures .................................................................................. 18

4.8.1 Overview.............................................................................................................................................. 18

4.8.2 Definition ............................................................................................................................................. 18

4.8.3 Condition A on path values ............................................................................................................... 19

4.8.4 Condition B on structure sharing ..................................................................................................... 19

4.8.5 Condition C on type ordering ............................................................................................................ 20

4.9 Operations on feature structures and feature values..................................................................... 21

4.9.1 Overview.............................................................................................................................................. 21

4.9.2 Compatibility ....................................................................................................................................... 21

4.9.3 Unification ........................................................................................................................................... 22

4.9.4 Unification of shared structures ....................................................................................................... 22

4.10 Operations on feature values and types .......................................................................................... 23

4.10.1 Concatenation and union operations ............................................................................................... 23

4.10.2 Alternation........................................................................................................................................... 24

4.10.3 Negation............................................................................................................................................... 25

4.11 Informal semantics of feature structures......................................................................................... 27

5 XML Representation of feature structures....................................................................................... 29

5.1 Overview.............................................................................................................................................. 29

5.2 Organization ........................................................................................................................................ 29

5.3 Elementary feature structures and the binary feature value.......................................................... 30

5.4 Other atomic feature values .............................................................................................................. 32

5.5 Feature and feature-value libraries ................................................................................................... 35

5.6 Feature structures as complex feature values ................................................................................37

5.7 Re-entrant feature structures ............................................................................................................ 40

5.8 Collections as complex feature values............................................................................................. 41

© ISO 2006 – All rights reserved iii
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SIST ISO 24610-1:2013
ISO 24610-1:2006(E)

5.9 Feature value expressions................................................................................................................. 44

5.9.1 Overview.............................................................................................................................................. 44

5.9.2 Alternation........................................................................................................................................... 44

5.9.3 Negation............................................................................................................................................... 47

5.9.4 Collection of values ............................................................................................................................ 48

5.10 Default values...................................................................................................................................... 48

5.11 Linking text and analysis ................................................................................................................... 50

Annex A (informative) Formal definitions and implementation of the XML representation of

feature structures................................................................................................................................ 54

A.1 Overview.............................................................................................................................................. 54

A.2 RELAX NG specification for the module .......................................................................................... 54

Annex B (informative) Examples for illustration ........................................................................................... 60

Annex C (informative) Type inheritance hierarchies..................................................................................... 62

C.1 Overview.............................................................................................................................................. 62

C.2 Definition.............................................................................................................................................. 62

C.3 Multiple inheritance ............................................................................................................................ 64

C.4 Type constraints ................................................................................................................................. 64

Annex D (informative) Denotational semantics of feature structure........................................................... 66

D.1 Feature structure signatures ............................................................................................................. 66

D.2 Feature structure algebra................................................................................................................... 66

D.3 FS domains.......................................................................................................................................... 67

D.4 Feature structure interpretations ...................................................................................................... 68

D.5 Satisfiability ......................................................................................................................................... 68

D.6 Subsumption ....................................................................................................................................... 68

D.7 Unification............................................................................................................................................ 69

Annex E (informative) Use of feature structures in applications................................................................. 70

E.1 Overview.............................................................................................................................................. 70

E.2 Phonological representation.............................................................................................................. 70

E.3 Grammar formalisms or theories ...................................................................................................... 70

E.4 Computational implementations ....................................................................................................... 71

Bibliography ..................................................................................................................................................... 75

iv © ISO 2006 – All rights reserved
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SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 24610-1 was prepared by Technical Committee ISO/TC 37, Terminology and other language and content

resources, Subcommittee SC 4, Language resource management.

ISO 24610 consists of the following parts, under the general title Language resource management — Feature

structures:
⎯ Part 1: Feature structure representation
The following part is under preparation:
⎯ Part 2: Feature system declaration
© ISO 2006 – All rights reserved v
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SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
Introduction

This part of ISO 24610 results from the agreement between the Text Encoding Initiative Consortium (TEI) and

the ISO TC 37/SC 4 that a joint activity should take place to revise the two existing chapters on feature

structures and feature system declaration in The TEI Guidelines called P4.
It is foreseen that ISO 24610 will have the following two parts.

⎯ Part 1, Feature structure representation, describes feature structures and their representation. It provides

an informal but explicit overview of their basic characteristics and formal semantics. In addition, part 1

defines a standard XML (eXtended Markup Language) vocabulary for the representation of untyped

feature structures, feature values, and feature libraries. It thus provides a reference format for the

exchange of feature structure representations between different application systems.

⎯ Part 2, Feature system declaration, discusses ways of validating typed feature structures which are

conformant to part 1, and of enforcing application-specific constraints. It proposes an XML vocabulary for

the representation of such constraints with reference to a set of features and the range of values

appropriate for them, and thus facilitates representation and validation of a type hierarchy as well as other

well-formedness conditions for particular applications, in particular those related to the goal of language

resource management.
vi © ISO 2006 – All rights reserved
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SIST ISO 24610-1:2013
INTERNATIONAL STANDARD ISO 24610-1:2006(E)
Language resource management — Feature structures —
Part 1:
Feature structure representation
1 Scope

Feature structures are an essential part of many linguistic formalisms as well as an underlying mechanism for

representing the information consumed or produced by and for language engineering applications. This part of

ISO 24610 provides a format for the representation, storage and exchange of feature structures in natural

language applications concerned with the annotation, production or analysis of linguistic data. It also defines a

computer format for the description of constraints that bear on a set of features, feature values, feature

specifications and operations on feature structures, thus offering a means of checking the conformance of

each feature structure with regards to a reference specification.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 8879, Information processing — Text and office systems — Standard Generalized Markup Language

(SGML), as extended by TC 2 (ISO/IEC JTC 1/SC 34 N029: 1998-12-06).

ISO 19757-2, Information technology — Document Schema Definition Language (DSDL) — Part 2: Regular-

grammar-based validation — RELAX NG

NOTE The first reference permits the use of XML and the second, RELAX NG,provides a specification for XML

modules. RELAX NG is a schema language for XML, standing for REgular LAnguage for XML for Next Generation, and

simplifies and extends the features of DTDs, Document Type Definitions.
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 8879 and ISO 19757-2 and the

following apply. This list is provided to clarify the terminology relating to feature structures used throughout

this part of ISO 24610. Terminology derived from XLM and other formal languages is not defined here.

3.1
alternation

operation on feature values (3.23) that returns one and only one of the values supplied as its argument

NOTE Given a feature specification F : a|b, where a|b denotes the alternation of a and b, F has either the value a or

the value b, but not both.
3.2
atomic value

value (3.23) without internal structure, i.e. value other than feature structure (3.10) and collection (3.4)

© ISO 2006 – All rights reserved 1
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SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
3.3
boxed label

label in box used in a matrix notation to denote a value shared by several features (3.8)

NOTE The label may be any alphanumeric symbol.
3.4
collection
list, set, or multiset of values (3.23)

NOTE A list is an ordered collection of entities some of which may be identical. A set is an unordered collection of

unique entities. A multiset is an unordered collection of entities that may or may not be unique; it is sometimes referred to

as a bag.
3.5
complex value

value (3.23) represented either as a feature structure (3.10) or as collection (3.4)

3.6
concatenation
operation of combining two lists of values (3.23) into a single list
3.7
empty feature structure
feature structure (3.10) containing no feature specifications (3.9)
3.8
feature
property of an entity

NOTE The combination of feature and feature-value constitutes a feature specification (3.9). For example, number

is a feature, singular is a value, and a pair is a feature specification.

3.9
feature specification
assignment of a value (3.23) to a feature (3.8)
NOTE Formally, it is treated as a pair of a feature and its value.
3.10
feature structure
set of feature specifications (3.9)
NOTE The minimum feature structure is the empty feature structure (3.7).
3.11
graph notation
notation of feature structure (3.10) in a single rooted graph
3.12
incompatibility

relation between two feature structures (3.10) which have conflicting types (3.19) or at least one common

feature (3.8) with incompatible values (3.23)

NOTE Two feature structures that are incompatible cannot be unified. The empty feature structure (3.7) is

compatible with any other feature structure.
2 © ISO 2006 – All rights reserved
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SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
3.13
matrix notation
attribute-value matrix
AVM
notation that uses square brackets to represent feature structures (3.10)

NOTE In a matrix notation, each row represents a feature specification (3.9), with the feature name and the feature

value separated by a colon (:), space ( ) or the equals sign (=).
3.14
merge

generic operation that includes union (3.22) of sets or multisets and concatenation (3.6) of lists

3.15
negation

(unary) operation on a value (3.23) denoting any other value incompatible with it

NOTE In this part of ISO 24610, negation applies to values only and is not understood as a truth function as in

ordinary bivalent logics.
3.16
path
sequence of labeled arcs connecting nodes in a graph
3.17
structure sharing
re-entrancy

relation between two or more features (3.8) within a feature structure (3.10) that share a value (3.23)

3.18
subsumption

relationship between two feature structures (3.10) in which one is more specific than the other

NOTE A feature structure A is said to subsume a feature structure B if A is at least as informative as B. Subsumption

is a reflexive, antisymmetric, and transitive relation between two feature structures.

3.19
type
name of a class of entities

NOTE Feature structures (3.10) may be characterized by grouping them into certain classes. Types are used to

name such classes.
3.20
typed feature structure
feature structure (3.10) labelled by a type (3.19)

NOTE In the graph notation (3.11), each node is labelled with a type. In the matrix notation (3.13), a type is

ordinarily placed at the upper left corner of the inside of the pair of square brackets that represents a typed feature

structure. In XML notation, the type is supplied as the value (3.23) of a type attribute on the element.

3.21
unification

operation that combines two compatible feature structures (3.10) into the least informative feature structure

that contains the information from the two
3.22
union
operation that combines two sets, or multisets, into one
NOTE The corresponding operation for lists is concatenation (3.6).
© ISO 2006 – All rights reserved 3
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SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
3.23
value
information about an entity

NOTE There are two kinds of feature values: atomic value (3.2) and complex value (3.5).

4 General characteristics of feature structure
4.1 Overview

A feature structure is a general purpose data structure that identifies and groups together individual features

by assigning a particular value to each. Because of the generality of feature structures, they can be used to

represent many different kinds of information. Interrelations among various pieces of information and their

instantiation in markup provide a meta-language for representing analysis and interpretation of linguistic

content. Moreover, this instantiation allows a specification of a set of features with values of specific types and

restrictions, by means of feature system declarations, or other XML mechanisms discussed in ISO 24610-2 .

4.2 Use of feature structures

Feature structures provide partial information about an object by specifying values for some or all of its

features. For example, if a female employee named Sandy Jones who is 30 years old is of the present

concern, then that person’s sex, name and age can be specified in a succinct manner by assigning a value to

each of these three features. These pieces of information can be put into a simple set notation, as in:

(1) Employee
{, , }

Feature structures are generally used as a vehicle for linguistic descriptions. For example, the phoneme /p/ in

English can be analysed in terms of its distinctive features: consonantal, anterior, voiceless, non-continuant or

stop sound segment, etc. Each of these features may be combined with one or other of the binary values

plus(+) and minus(-) to provide a feature specification. In a phonemic analysis such as the following, the value

of a feature specifies the presence or absence of that feature:
(2) Sound segment /p/
{, , , }

In such an analysis, the sound segment /p/ is distinguished from other phonemes in terms of the presence or

absence of specific features. For example, /p/ differs from the phoneme /b/ in VOICING, and from /k/ in

articulatory position: one is articulated at the anterior, (the lip or alveolar area of the mouth), and the other at

the nonanterior, namely the back of the oral cavity.

This feature analysis can be extended to other kinds of description. Consider a verb like “love”. Its features

include both syntactic and semantic properties: as a transitive verb, it takes an object as well as a subject as

its arguments, expressing the semantic relation of loving between two persons or animate beings. The exact

representation of these feature specifications requires a detailed elaboration of what feature structures are.

For now, these grammatical features can be roughly represented in a set format like the following:

(3) Grammatical features of the verb “love”
{, , },
where POS stands for part of speech.
1) Under preparation.
4 © ISO 2006 – All rights reserved
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SIST ISO 24610-1:2013
ISO 24610-1:2006(E)

Since its first extensive use in generative phonology in mid-60s, the feature structure formalism has become

an essential tool not only for phonology, but more generally in support of syntax and semantics as well as

lexicon building, especially in computational work. Feature structures are used to describe and model

linguistic entities and phenomena by specifying their properties. In the next clauses, some of the formal

properties of feature structures are outlined together with means of representing them in a systematic manner.

4.3 Basic concepts

Feature structures may be viewed in a variety of ways. The most common and perhaps the most intuitive

views are the following:

⎯ a set of feature specifications that consists of pairs of features and their values;

⎯ labelled directed graphs with a single root where each arc is labelled with the name of a feature and

directed to its value.

In set-theoretic terms, a feature structure FS can be defined as a partial function from a set Feat of features to

a set FeatVal of values, where FeatVal consists of a set AtomVal of atomic values and a set FS of feature

structures.
(4) A feature structure as a set or partial function
FS ⊆ {⎥F∈Feat,v∈FeatVal}
i i i i
or
FS : Feat ⎯→FeatVal
where FeatVal = AtomVal∪ FS a
...

INTERNATIONAL ISO
STANDARD 24610-1
FIrst edition
2006-04-15
Language resource management —
Feature structures —
Part 1:
Feature structure representation
Gestion des ressources linguistiques — Structures de traits —
Partie 1: Représentation de structures de traits
Reference number
ISO 24610-1:2006(E)
ISO 2006
---------------------- Page: 1 ----------------------
ISO 24610-1:2006(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but

shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In

the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

© ISO 2006

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2006 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 24610-1:2006(E)
Contents Page

Foreword............................................................................................................................................................. v

Introduction ....................................................................................................................................................... vi

1 Scope..................................................................................................................................................... 1

2 Normative references........................................................................................................................... 1

3 Terms and definitions........................................................................................................................... 1

4 General characteristics of feature structure...................................................................................... 4

4.1 Overview................................................................................................................................................ 4

4.2 Use of feature structures ..................................................................................................................... 4

4.3 Basic concepts...................................................................................................................................... 5

4.4 Notations ............................................................................................................................................... 5

4.4.1 Overview................................................................................................................................................ 5

4.4.2 Graph notation ...................................................................................................................................... 6

4.4.3 Matrix notation ...................................................................................................................................... 7

4.4.4 XML-based notation.............................................................................................................................. 8

4.5 Structure sharing................................................................................................................................ 10

4.6 Collections as complex feature values............................................................................................. 12

4.6.1 Overview.............................................................................................................................................. 12

4.6.2 Lists as feature values ....................................................................................................................... 12

4.6.3 Sets as feature values ........................................................................................................................ 14

4.6.4 Multisets as feature values ................................................................................................................ 15

4.7 Typed feature structure...................................................................................................................... 16

4.7.1 Overview.............................................................................................................................................. 16

4.7.2 Types.................................................................................................................................................... 16

4.7.3 Notations ............................................................................................................................................. 16

4.8 Subsumption: relation on feature structures .................................................................................. 18

4.8.1 Overview.............................................................................................................................................. 18

4.8.2 Definition ............................................................................................................................................. 18

4.8.3 Condition A on path values ............................................................................................................... 19

4.8.4 Condition B on structure sharing ..................................................................................................... 19

4.8.5 Condition C on type ordering ............................................................................................................ 20

4.9 Operations on feature structures and feature values..................................................................... 21

4.9.1 Overview.............................................................................................................................................. 21

4.9.2 Compatibility ....................................................................................................................................... 21

4.9.3 Unification ........................................................................................................................................... 22

4.9.4 Unification of shared structures ....................................................................................................... 22

4.10 Operations on feature values and types .......................................................................................... 23

4.10.1 Concatenation and union operations ............................................................................................... 23

4.10.2 Alternation........................................................................................................................................... 24

4.10.3 Negation............................................................................................................................................... 25

4.11 Informal semantics of feature structures......................................................................................... 27

5 XML Representation of feature structures....................................................................................... 29

5.1 Overview.............................................................................................................................................. 29

5.2 Organization ........................................................................................................................................ 29

5.3 Elementary feature structures and the binary feature value.......................................................... 30

5.4 Other atomic feature values .............................................................................................................. 32

5.5 Feature and feature-value libraries ................................................................................................... 35

5.6 Feature structures as complex feature values ................................................................................37

5.7 Re-entrant feature structures ............................................................................................................ 40

5.8 Collections as complex feature values............................................................................................. 41

© ISO 2006 – All rights reserved iii
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ISO 24610-1:2006(E)

5.9 Feature value expressions................................................................................................................. 44

5.9.1 Overview.............................................................................................................................................. 44

5.9.2 Alternation........................................................................................................................................... 44

5.9.3 Negation............................................................................................................................................... 47

5.9.4 Collection of values ............................................................................................................................ 48

5.10 Default values...................................................................................................................................... 48

5.11 Linking text and analysis ................................................................................................................... 50

Annex A (informative) Formal definitions and implementation of the XML representation of

feature structures................................................................................................................................ 54

A.1 Overview.............................................................................................................................................. 54

A.2 RELAX NG specification for the module .......................................................................................... 54

Annex B (informative) Examples for illustration ........................................................................................... 60

Annex C (informative) Type inheritance hierarchies..................................................................................... 62

C.1 Overview.............................................................................................................................................. 62

C.2 Definition.............................................................................................................................................. 62

C.3 Multiple inheritance ............................................................................................................................ 64

C.4 Type constraints ................................................................................................................................. 64

Annex D (informative) Denotational semantics of feature structure........................................................... 66

D.1 Feature structure signatures ............................................................................................................. 66

D.2 Feature structure algebra................................................................................................................... 66

D.3 FS domains.......................................................................................................................................... 67

D.4 Feature structure interpretations ...................................................................................................... 68

D.5 Satisfiability ......................................................................................................................................... 68

D.6 Subsumption ....................................................................................................................................... 68

D.7 Unification............................................................................................................................................ 69

Annex E (informative) Use of feature structures in applications................................................................. 70

E.1 Overview.............................................................................................................................................. 70

E.2 Phonological representation.............................................................................................................. 70

E.3 Grammar formalisms or theories ...................................................................................................... 70

E.4 Computational implementations ....................................................................................................... 71

Bibliography ..................................................................................................................................................... 75

iv © ISO 2006 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 24610-1:2006(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 24610-1 was prepared by Technical Committee ISO/TC 37, Terminology and other language and content

resources, Subcommittee SC 4, Language resource management.

ISO 24610 consists of the following parts, under the general title Language resource management — Feature

structures:
⎯ Part 1: Feature structure representation
The following part is under preparation:
⎯ Part 2: Feature system declaration
© ISO 2006 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 24610-1:2006(E)
Introduction

This part of ISO 24610 results from the agreement between the Text Encoding Initiative Consortium (TEI) and

the ISO TC 37/SC 4 that a joint activity should take place to revise the two existing chapters on feature

structures and feature system declaration in The TEI Guidelines called P4.
It is foreseen that ISO 24610 will have the following two parts.

⎯ Part 1, Feature structure representation, describes feature structures and their representation. It provides

an informal but explicit overview of their basic characteristics and formal semantics. In addition, part 1

defines a standard XML (eXtended Markup Language) vocabulary for the representation of untyped

feature structures, feature values, and feature libraries. It thus provides a reference format for the

exchange of feature structure representations between different application systems.

⎯ Part 2, Feature system declaration, discusses ways of validating typed feature structures which are

conformant to part 1, and of enforcing application-specific constraints. It proposes an XML vocabulary for

the representation of such constraints with reference to a set of features and the range of values

appropriate for them, and thus facilitates representation and validation of a type hierarchy as well as other

well-formedness conditions for particular applications, in particular those related to the goal of language

resource management.
vi © ISO 2006 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 24610-1:2006(E)
Language resource management — Feature structures —
Part 1:
Feature structure representation
1 Scope

Feature structures are an essential part of many linguistic formalisms as well as an underlying mechanism for

representing the information consumed or produced by and for language engineering applications. This part of

ISO 24610 provides a format for the representation, storage and exchange of feature structures in natural

language applications concerned with the annotation, production or analysis of linguistic data. It also defines a

computer format for the description of constraints that bear on a set of features, feature values, feature

specifications and operations on feature structures, thus offering a means of checking the conformance of

each feature structure with regards to a reference specification.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 8879, Information processing — Text and office systems — Standard Generalized Markup Language

(SGML), as extended by TC 2 (ISO/IEC JTC 1/SC 34 N029: 1998-12-06).

ISO 19757-2, Information technology — Document Schema Definition Language (DSDL) — Part 2: Regular-

grammar-based validation — RELAX NG

NOTE The first reference permits the use of XML and the second, RELAX NG,provides a specification for XML

modules. RELAX NG is a schema language for XML, standing for REgular LAnguage for XML for Next Generation, and

simplifies and extends the features of DTDs, Document Type Definitions.
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 8879 and ISO 19757-2 and the

following apply. This list is provided to clarify the terminology relating to feature structures used throughout

this part of ISO 24610. Terminology derived from XLM and other formal languages is not defined here.

3.1
alternation

operation on feature values (3.23) that returns one and only one of the values supplied as its argument

NOTE Given a feature specification F : a|b, where a|b denotes the alternation of a and b, F has either the value a or

the value b, but not both.
3.2
atomic value

value (3.23) without internal structure, i.e. value other than feature structure (3.10) and collection (3.4)

© ISO 2006 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO 24610-1:2006(E)
3.3
boxed label

label in box used in a matrix notation to denote a value shared by several features (3.8)

NOTE The label may be any alphanumeric symbol.
3.4
collection
list, set, or multiset of values (3.23)

NOTE A list is an ordered collection of entities some of which may be identical. A set is an unordered collection of

unique entities. A multiset is an unordered collection of entities that may or may not be unique; it is sometimes referred to

as a bag.
3.5
complex value

value (3.23) represented either as a feature structure (3.10) or as collection (3.4)

3.6
concatenation
operation of combining two lists of values (3.23) into a single list
3.7
empty feature structure
feature structure (3.10) containing no feature specifications (3.9)
3.8
feature
property of an entity

NOTE The combination of feature and feature-value constitutes a feature specification (3.9). For example, number

is a feature, singular is a value, and a pair is a feature specification.

3.9
feature specification
assignment of a value (3.23) to a feature (3.8)
NOTE Formally, it is treated as a pair of a feature and its value.
3.10
feature structure
set of feature specifications (3.9)
NOTE The minimum feature structure is the empty feature structure (3.7).
3.11
graph notation
notation of feature structure (3.10) in a single rooted graph
3.12
incompatibility

relation between two feature structures (3.10) which have conflicting types (3.19) or at least one common

feature (3.8) with incompatible values (3.23)

NOTE Two feature structures that are incompatible cannot be unified. The empty feature structure (3.7) is

compatible with any other feature structure.
2 © ISO 2006 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 24610-1:2006(E)
3.13
matrix notation
attribute-value matrix
AVM
notation that uses square brackets to represent feature structures (3.10)

NOTE In a matrix notation, each row represents a feature specification (3.9), with the feature name and the feature

value separated by a colon (:), space ( ) or the equals sign (=).
3.14
merge

generic operation that includes union (3.22) of sets or multisets and concatenation (3.6) of lists

3.15
negation

(unary) operation on a value (3.23) denoting any other value incompatible with it

NOTE In this part of ISO 24610, negation applies to values only and is not understood as a truth function as in

ordinary bivalent logics.
3.16
path
sequence of labeled arcs connecting nodes in a graph
3.17
structure sharing
re-entrancy

relation between two or more features (3.8) within a feature structure (3.10) that share a value (3.23)

3.18
subsumption

relationship between two feature structures (3.10) in which one is more specific than the other

NOTE A feature structure A is said to subsume a feature structure B if A is at least as informative as B. Subsumption

is a reflexive, antisymmetric, and transitive relation between two feature structures.

3.19
type
name of a class of entities

NOTE Feature structures (3.10) may be characterized by grouping them into certain classes. Types are used to

name such classes.
3.20
typed feature structure
feature structure (3.10) labelled by a type (3.19)

NOTE In the graph notation (3.11), each node is labelled with a type. In the matrix notation (3.13), a type is

ordinarily placed at the upper left corner of the inside of the pair of square brackets that represents a typed feature

structure. In XML notation, the type is supplied as the value (3.23) of a type attribute on the element.

3.21
unification

operation that combines two compatible feature structures (3.10) into the least informative feature structure

that contains the information from the two
3.22
union
operation that combines two sets, or multisets, into one
NOTE The corresponding operation for lists is concatenation (3.6).
© ISO 2006 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO 24610-1:2006(E)
3.23
value
information about an entity

NOTE There are two kinds of feature values: atomic value (3.2) and complex value (3.5).

4 General characteristics of feature structure
4.1 Overview

A feature structure is a general purpose data structure that identifies and groups together individual features

by assigning a particular value to each. Because of the generality of feature structures, they can be used to

represent many different kinds of information. Interrelations among various pieces of information and their

instantiation in markup provide a meta-language for representing analysis and interpretation of linguistic

content. Moreover, this instantiation allows a specification of a set of features with values of specific types and

restrictions, by means of feature system declarations, or other XML mechanisms discussed in ISO 24610-2 .

4.2 Use of feature structures

Feature structures provide partial information about an object by specifying values for some or all of its

features. For example, if a female employee named Sandy Jones who is 30 years old is of the present

concern, then that person’s sex, name and age can be specified in a succinct manner by assigning a value to

each of these three features. These pieces of information can be put into a simple set notation, as in:

(1) Employee
{, , }

Feature structures are generally used as a vehicle for linguistic descriptions. For example, the phoneme /p/ in

English can be analysed in terms of its distinctive features: consonantal, anterior, voiceless, non-continuant or

stop sound segment, etc. Each of these features may be combined with one or other of the binary values

plus(+) and minus(-) to provide a feature specification. In a phonemic analysis such as the following, the value

of a feature specifies the presence or absence of that feature:
(2) Sound segment /p/
{, , , }

In such an analysis, the sound segment /p/ is distinguished from other phonemes in terms of the presence or

absence of specific features. For example, /p/ differs from the phoneme /b/ in VOICING, and from /k/ in

articulatory position: one is articulated at the anterior, (the lip or alveolar area of the mouth), and the other at

the nonanterior, namely the back of the oral cavity.

This feature analysis can be extended to other kinds of description. Consider a verb like “love”. Its features

include both syntactic and semantic properties: as a transitive verb, it takes an object as well as a subject as

its arguments, expressing the semantic relation of loving between two persons or animate beings. The exact

representation of these feature specifications requires a detailed elaboration of what feature structures are.

For now, these grammatical features can be roughly represented in a set format like the following:

(3) Grammatical features of the verb “love”
{, , },
where POS stands for part of speech.
1) Under preparation.
4 © ISO 2006 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 24610-1:2006(E)

Since its first extensive use in generative phonology in mid-60s, the feature structure formalism has become

an essential tool not only for phonology, but more generally in support of syntax and semantics as well as

lexicon building, especially in computational work. Feature structures are used to describe and model

linguistic entities and phenomena by specifying their properties. In the next clauses, some of the formal

properties of feature structures are outlined together with means of representing them in a systematic manner.

4.3 Basic concepts

Feature structures may be viewed in a variety of ways. The most common and perhaps the most intuitive

views are the following:

⎯ a set of feature specifications that consists of pairs of features and their values;

⎯ labelled directed graphs with a single root where each arc is labelled with the name of a feature and

directed to its value.

In set-theoretic terms, a feature structure FS can be defined as a partial function from a set Feat of features to

a set FeatVal of values, where FeatVal consists of a set AtomVal of atomic values and a set FS of feature

structures.
(4) A feature structure as a set or partial function
FS ⊆ {⎥F∈Feat,v∈FeatVal}
i i i i
or
FS : Feat ⎯→FeatVal
where FeatVal = AtomVal∪ FS and where FeatVal stands for all possible values.

Values may be regarded as either atomic or complex. Atomic values are entities without internal structure,

while complex values may be feature structures or collections of values (either complex or atomic).

NOTE These two definitions are not absolutely equivalent, for in a set there may be more than one value, v, for a

feature, F.

For example, the part of speech (POS) feature can take the name of an atomic morpho-syntactic category

such as verb as its value. Conversely, the agreement (AGR) feature in English takes a complex value in the

form of a feature structure with features PERSON and NUMBER. The word “loves”, for instance, has a POS

feature with the value “verb”, while the value of its AGR feature consists of a feature structure comprising two

feature specifications: PERSON with the value “3rd”, and NUMBER with the value “singular”.

4.4 Notations
4.4.1 Overview

As a list of feature-value pairs, the overall form of a feature structure is simple. However, the internal structure

of a feature structure may be complex when a feature structure contains either
a) a feature whose value is itself a feature structure, or
b) a multi-valued feature wh
...

SLOVENSKI STANDARD
SIST ISO 24610-1:2013
01-julij-2013

Upravljanje z jezikovnimi viri - Strukture lastnosti - 1. del: Predstavitev struktur

lastnosti
Language resource management -- Feature structures -- Part 1: Feature structure
representation

Gestion des ressources linguistiques -- Structures de traits -- Partie 1: Représentation de

structures de traits
Ta slovenski standard je istoveten z: ISO 24610-1:2006
ICS:
01.140.20 Informacijske vede Information sciences
SIST ISO 24610-1:2013 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO 24610-1:2013
---------------------- Page: 2 ----------------------
SIST ISO 24610-1:2013
INTERNATIONAL ISO
STANDARD 24610-1
FIrst edition
2006-04-15
Language resource management —
Feature structures —
Part 1:
Feature structure representation
Gestion des ressources linguistiques — Structures de traits —
Partie 1: Représentation de structures de traits
Reference number
ISO 24610-1:2006(E)
ISO 2006
---------------------- Page: 3 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
PDF disclaimer

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© ISO 2006

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Published in Switzerland
ii © ISO 2006 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
Contents Page

Foreword............................................................................................................................................................. v

Introduction ....................................................................................................................................................... vi

1 Scope..................................................................................................................................................... 1

2 Normative references........................................................................................................................... 1

3 Terms and definitions........................................................................................................................... 1

4 General characteristics of feature structure...................................................................................... 4

4.1 Overview................................................................................................................................................ 4

4.2 Use of feature structures ..................................................................................................................... 4

4.3 Basic concepts...................................................................................................................................... 5

4.4 Notations ............................................................................................................................................... 5

4.4.1 Overview................................................................................................................................................ 5

4.4.2 Graph notation ...................................................................................................................................... 6

4.4.3 Matrix notation ...................................................................................................................................... 7

4.4.4 XML-based notation.............................................................................................................................. 8

4.5 Structure sharing................................................................................................................................ 10

4.6 Collections as complex feature values............................................................................................. 12

4.6.1 Overview.............................................................................................................................................. 12

4.6.2 Lists as feature values ....................................................................................................................... 12

4.6.3 Sets as feature values ........................................................................................................................ 14

4.6.4 Multisets as feature values ................................................................................................................ 15

4.7 Typed feature structure...................................................................................................................... 16

4.7.1 Overview.............................................................................................................................................. 16

4.7.2 Types.................................................................................................................................................... 16

4.7.3 Notations ............................................................................................................................................. 16

4.8 Subsumption: relation on feature structures .................................................................................. 18

4.8.1 Overview.............................................................................................................................................. 18

4.8.2 Definition ............................................................................................................................................. 18

4.8.3 Condition A on path values ............................................................................................................... 19

4.8.4 Condition B on structure sharing ..................................................................................................... 19

4.8.5 Condition C on type ordering ............................................................................................................ 20

4.9 Operations on feature structures and feature values..................................................................... 21

4.9.1 Overview.............................................................................................................................................. 21

4.9.2 Compatibility ....................................................................................................................................... 21

4.9.3 Unification ........................................................................................................................................... 22

4.9.4 Unification of shared structures ....................................................................................................... 22

4.10 Operations on feature values and types .......................................................................................... 23

4.10.1 Concatenation and union operations ............................................................................................... 23

4.10.2 Alternation........................................................................................................................................... 24

4.10.3 Negation............................................................................................................................................... 25

4.11 Informal semantics of feature structures......................................................................................... 27

5 XML Representation of feature structures....................................................................................... 29

5.1 Overview.............................................................................................................................................. 29

5.2 Organization ........................................................................................................................................ 29

5.3 Elementary feature structures and the binary feature value.......................................................... 30

5.4 Other atomic feature values .............................................................................................................. 32

5.5 Feature and feature-value libraries ................................................................................................... 35

5.6 Feature structures as complex feature values ................................................................................37

5.7 Re-entrant feature structures ............................................................................................................ 40

5.8 Collections as complex feature values............................................................................................. 41

© ISO 2006 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)

5.9 Feature value expressions................................................................................................................. 44

5.9.1 Overview.............................................................................................................................................. 44

5.9.2 Alternation........................................................................................................................................... 44

5.9.3 Negation............................................................................................................................................... 47

5.9.4 Collection of values ............................................................................................................................ 48

5.10 Default values...................................................................................................................................... 48

5.11 Linking text and analysis ................................................................................................................... 50

Annex A (informative) Formal definitions and implementation of the XML representation of

feature structures................................................................................................................................ 54

A.1 Overview.............................................................................................................................................. 54

A.2 RELAX NG specification for the module .......................................................................................... 54

Annex B (informative) Examples for illustration ........................................................................................... 60

Annex C (informative) Type inheritance hierarchies..................................................................................... 62

C.1 Overview.............................................................................................................................................. 62

C.2 Definition.............................................................................................................................................. 62

C.3 Multiple inheritance ............................................................................................................................ 64

C.4 Type constraints ................................................................................................................................. 64

Annex D (informative) Denotational semantics of feature structure........................................................... 66

D.1 Feature structure signatures ............................................................................................................. 66

D.2 Feature structure algebra................................................................................................................... 66

D.3 FS domains.......................................................................................................................................... 67

D.4 Feature structure interpretations ...................................................................................................... 68

D.5 Satisfiability ......................................................................................................................................... 68

D.6 Subsumption ....................................................................................................................................... 68

D.7 Unification............................................................................................................................................ 69

Annex E (informative) Use of feature structures in applications................................................................. 70

E.1 Overview.............................................................................................................................................. 70

E.2 Phonological representation.............................................................................................................. 70

E.3 Grammar formalisms or theories ...................................................................................................... 70

E.4 Computational implementations ....................................................................................................... 71

Bibliography ..................................................................................................................................................... 75

iv © ISO 2006 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 24610-1 was prepared by Technical Committee ISO/TC 37, Terminology and other language and content

resources, Subcommittee SC 4, Language resource management.

ISO 24610 consists of the following parts, under the general title Language resource management — Feature

structures:
⎯ Part 1: Feature structure representation
The following part is under preparation:
⎯ Part 2: Feature system declaration
© ISO 2006 – All rights reserved v
---------------------- Page: 7 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
Introduction

This part of ISO 24610 results from the agreement between the Text Encoding Initiative Consortium (TEI) and

the ISO TC 37/SC 4 that a joint activity should take place to revise the two existing chapters on feature

structures and feature system declaration in The TEI Guidelines called P4.
It is foreseen that ISO 24610 will have the following two parts.

⎯ Part 1, Feature structure representation, describes feature structures and their representation. It provides

an informal but explicit overview of their basic characteristics and formal semantics. In addition, part 1

defines a standard XML (eXtended Markup Language) vocabulary for the representation of untyped

feature structures, feature values, and feature libraries. It thus provides a reference format for the

exchange of feature structure representations between different application systems.

⎯ Part 2, Feature system declaration, discusses ways of validating typed feature structures which are

conformant to part 1, and of enforcing application-specific constraints. It proposes an XML vocabulary for

the representation of such constraints with reference to a set of features and the range of values

appropriate for them, and thus facilitates representation and validation of a type hierarchy as well as other

well-formedness conditions for particular applications, in particular those related to the goal of language

resource management.
vi © ISO 2006 – All rights reserved
---------------------- Page: 8 ----------------------
SIST ISO 24610-1:2013
INTERNATIONAL STANDARD ISO 24610-1:2006(E)
Language resource management — Feature structures —
Part 1:
Feature structure representation
1 Scope

Feature structures are an essential part of many linguistic formalisms as well as an underlying mechanism for

representing the information consumed or produced by and for language engineering applications. This part of

ISO 24610 provides a format for the representation, storage and exchange of feature structures in natural

language applications concerned with the annotation, production or analysis of linguistic data. It also defines a

computer format for the description of constraints that bear on a set of features, feature values, feature

specifications and operations on feature structures, thus offering a means of checking the conformance of

each feature structure with regards to a reference specification.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 8879, Information processing — Text and office systems — Standard Generalized Markup Language

(SGML), as extended by TC 2 (ISO/IEC JTC 1/SC 34 N029: 1998-12-06).

ISO 19757-2, Information technology — Document Schema Definition Language (DSDL) — Part 2: Regular-

grammar-based validation — RELAX NG

NOTE The first reference permits the use of XML and the second, RELAX NG,provides a specification for XML

modules. RELAX NG is a schema language for XML, standing for REgular LAnguage for XML for Next Generation, and

simplifies and extends the features of DTDs, Document Type Definitions.
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 8879 and ISO 19757-2 and the

following apply. This list is provided to clarify the terminology relating to feature structures used throughout

this part of ISO 24610. Terminology derived from XLM and other formal languages is not defined here.

3.1
alternation

operation on feature values (3.23) that returns one and only one of the values supplied as its argument

NOTE Given a feature specification F : a|b, where a|b denotes the alternation of a and b, F has either the value a or

the value b, but not both.
3.2
atomic value

value (3.23) without internal structure, i.e. value other than feature structure (3.10) and collection (3.4)

© ISO 2006 – All rights reserved 1
---------------------- Page: 9 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
3.3
boxed label

label in box used in a matrix notation to denote a value shared by several features (3.8)

NOTE The label may be any alphanumeric symbol.
3.4
collection
list, set, or multiset of values (3.23)

NOTE A list is an ordered collection of entities some of which may be identical. A set is an unordered collection of

unique entities. A multiset is an unordered collection of entities that may or may not be unique; it is sometimes referred to

as a bag.
3.5
complex value

value (3.23) represented either as a feature structure (3.10) or as collection (3.4)

3.6
concatenation
operation of combining two lists of values (3.23) into a single list
3.7
empty feature structure
feature structure (3.10) containing no feature specifications (3.9)
3.8
feature
property of an entity

NOTE The combination of feature and feature-value constitutes a feature specification (3.9). For example, number

is a feature, singular is a value, and a pair is a feature specification.

3.9
feature specification
assignment of a value (3.23) to a feature (3.8)
NOTE Formally, it is treated as a pair of a feature and its value.
3.10
feature structure
set of feature specifications (3.9)
NOTE The minimum feature structure is the empty feature structure (3.7).
3.11
graph notation
notation of feature structure (3.10) in a single rooted graph
3.12
incompatibility

relation between two feature structures (3.10) which have conflicting types (3.19) or at least one common

feature (3.8) with incompatible values (3.23)

NOTE Two feature structures that are incompatible cannot be unified. The empty feature structure (3.7) is

compatible with any other feature structure.
2 © ISO 2006 – All rights reserved
---------------------- Page: 10 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
3.13
matrix notation
attribute-value matrix
AVM
notation that uses square brackets to represent feature structures (3.10)

NOTE In a matrix notation, each row represents a feature specification (3.9), with the feature name and the feature

value separated by a colon (:), space ( ) or the equals sign (=).
3.14
merge

generic operation that includes union (3.22) of sets or multisets and concatenation (3.6) of lists

3.15
negation

(unary) operation on a value (3.23) denoting any other value incompatible with it

NOTE In this part of ISO 24610, negation applies to values only and is not understood as a truth function as in

ordinary bivalent logics.
3.16
path
sequence of labeled arcs connecting nodes in a graph
3.17
structure sharing
re-entrancy

relation between two or more features (3.8) within a feature structure (3.10) that share a value (3.23)

3.18
subsumption

relationship between two feature structures (3.10) in which one is more specific than the other

NOTE A feature structure A is said to subsume a feature structure B if A is at least as informative as B. Subsumption

is a reflexive, antisymmetric, and transitive relation between two feature structures.

3.19
type
name of a class of entities

NOTE Feature structures (3.10) may be characterized by grouping them into certain classes. Types are used to

name such classes.
3.20
typed feature structure
feature structure (3.10) labelled by a type (3.19)

NOTE In the graph notation (3.11), each node is labelled with a type. In the matrix notation (3.13), a type is

ordinarily placed at the upper left corner of the inside of the pair of square brackets that represents a typed feature

structure. In XML notation, the type is supplied as the value (3.23) of a type attribute on the element.

3.21
unification

operation that combines two compatible feature structures (3.10) into the least informative feature structure

that contains the information from the two
3.22
union
operation that combines two sets, or multisets, into one
NOTE The corresponding operation for lists is concatenation (3.6).
© ISO 2006 – All rights reserved 3
---------------------- Page: 11 ----------------------
SIST ISO 24610-1:2013
ISO 24610-1:2006(E)
3.23
value
information about an entity

NOTE There are two kinds of feature values: atomic value (3.2) and complex value (3.5).

4 General characteristics of feature structure
4.1 Overview

A feature structure is a general purpose data structure that identifies and groups together individual features

by assigning a particular value to each. Because of the generality of feature structures, they can be used to

represent many different kinds of information. Interrelations among various pieces of information and their

instantiation in markup provide a meta-language for representing analysis and interpretation of linguistic

content. Moreover, this instantiation allows a specification of a set of features with values of specific types and

restrictions, by means of feature system declarations, or other XML mechanisms discussed in ISO 24610-2 .

4.2 Use of feature structures

Feature structures provide partial information about an object by specifying values for some or all of its

features. For example, if a female employee named Sandy Jones who is 30 years old is of the present

concern, then that person’s sex, name and age can be specified in a succinct manner by assigning a value to

each of these three features. These pieces of information can be put into a simple set notation, as in:

(1) Employee
{, , }

Feature structures are generally used as a vehicle for linguistic descriptions. For example, the phoneme /p/ in

English can be analysed in terms of its distinctive features: consonantal, anterior, voiceless, non-continuant or

stop sound segment, etc. Each of these features may be combined with one or other of the binary values

plus(+) and minus(-) to provide a feature specification. In a phonemic analysis such as the following, the value

of a feature specifies the presence or absence of that feature:
(2) Sound segment /p/
{, , , }

In such an analysis, the sound segment /p/ is distinguished from other phonemes in terms of the presence or

absence of specific features. For example, /p/ differs from the phoneme /b/ in VOICING, and from /k/ in

articulatory position: one is articulated at the anterior, (the lip or alveolar area of the mouth), and the other at

the nonanterior, namely the back of the oral cavity.

This feature analysis can be extended to other kinds of description. Consider a verb like “love”. Its features

include both syntactic and semantic properties: as a transitive verb, it takes an object as well as a subject as

its arguments, expressing the semantic relation of loving between two persons or animate beings. The exact

representation of these feature specifications requires a detailed elaboration of what feature structures are.

For now, these grammatical features can be roughly represented in a set format like the following:

(3) Grammatical features of the verb “love”
{, , },
where POS stands for part of speech.
1) Under preparation.
4 © ISO 2006 – All rights reserved
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SIST ISO 24610-1:2013
ISO 24610-1:2006(E)

Since its first extensive use in generative phonology in mid-60s, the feature structure formalism has become

an essential tool not only for phonology, but more generally in support of syntax and semantics as well as

lexicon building, especially in computational work. Feature structures are used to describe and model

linguistic entities and phenomena by specifying their properties. In the next clauses, some of the formal

properties of feature structures are outlined together with means of representing them in a systematic manner.

4.3 Basic concepts

Feature structures may be viewed in a variety of ways. The most common and perhaps the most intuitive

views are the following:

⎯ a set of feature specifications that consists of pairs of features and their values;

⎯ labelled directed graphs with a single root where each arc is labelled with the name of a feature and

directed to its value.

In set-theoretic terms, a feature structure FS can be defined as a partial function from a set Feat of features to

a set FeatVal of values, where FeatVal consists of a set AtomVal of atomic values and a set FS of feature

structures.
(4) A feature structure as a set or partial function
FS ⊆ {⎥F∈Feat,v∈FeatVal}
i i i i
or
FS : Feat ⎯→FeatVal
where FeatVal = AtomVal∪ FS and where FeatVal stands for all possible values.

Values may be regarded as either atomic or complex. Atomic values are entities without internal structure,

while complex values may be feature structures or
...

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