ISO/TR 10303-12:1997

Industrial automation systems and integration — Product data representation and exchange — Part 12: Description methods: The EXPRESS-I language reference manual

Systèmes d'automatisation industrielle et intégration — Représentation et échange de données de produits — Partie 12: Méthodes descriptives: Le manuel de référence du langage EXPRESS-I

General Information

• Status: Withdrawn
• Publication Date: 23-Jul-1997
• Withdrawal Date: 23-Jul-1997
• ICS: 25.040.40 - Industrial process measurement and control
• Technical Committee: ISO/TC 184/SC 4 - Industrial data
• Drafting Committee: ISO/TC 184/SC 4/WG 11 - Implementation methods and conformance methods
• Current Stage: 9599 - Withdrawal of International Standard
• Completion Date: 10-Dec-2013

Standards Content (Sample)

ISO/TR
TECHNICAL
10303-I 2
REPORT
First edition
1997-07-I 5
Industrial automation systems and
integration - Product data representation
and exchange -
Part 12:
Description methods: The EXPRESS-l
language reference manual
Syst&mes d’automatisation industrielle et intggration - t?epr&entation et
Bchange de don&es de produits -
Parfie 12: M&hodes descriptives: Le manuel de rkfkrence du langage
EXPRESS-I
Reference number
ISOTTR 10303-12:1997(E)

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ISO/TR 1030342:1997(E)
Page
Contents
1
1 Scope .
.....................................
2
2 Normative references
..........................................
3 Definitions. 3
............................
3
. Terms defined in IS0 10303-l
31
...........................
3
. Terms defined in IS0 10303-11
32
...........................
3
33 . Terms defined in IS0 10303-31
................................... 4
. Other definitions
34
....................................
4
3.4.1 attribute
................................ 4
3.4.2 information base
................................... 4
object base
3.4.3
4
3.4.4 schema .
4
.....................................
3.4.5 type.
4
..............................
universe of discourse
3.4.6
..................................
4 Conformance requirements
...................
41 . Formal specifications written in EXPRESS-I
...............................
Conformance levels
4.1.1
..........................
. Implementations of EXPRESS-I
42
................................... 6
5 Fundamental principles
...................................... 7
6 Language elements
..................................... 7
61 . Character set
7
6.1.1 Digits .
..................................... 8
6.1.2 Letters
............................ 8
Special characters . .’
6.1.3
................................... 8
6.1.4 Underscore
................................... 8
Whitespace
6.1.5
.................................... 9
6.1.6 Remarks
................................... 10
62 . Reserved words.
.................................... 10
6.2.1 Keywords
..................... 11
Reserved words which are operators
6.2.2
............................... 11
Built-in constants
6.2.3
@ IS0 1997
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 the publisher.
International Organization for Standardization
Case Postale 56 l CH-2111 Genhve 20 l Switzerland
Printed in Switzerland
ii

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ISO/TR lo303=12:1997(E)
@IS0
11
6.2.4 Built-in functions . . . . . . . . . . . . . . . . . . . . . . . ,. . . . . . . .
11
6.2.5 Built-in procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
. Symbols.
63
12
64 . Identifiers and references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
7 Named domains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
71 . Entity domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
72 . Enumeration domain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
. .
73 . Select domain . . .
15
. . .
74 Type domain . . .
. 16
8 Values and instances . . . .
. 16
.................................
81 . Base values . . . .
. 16
.................................
8.1.1 Binary value
l 16
.................................
8.1.2 Boolean value
16
Number value .
8.1.3
17
&lc4 Integer value .
17
..................................
82.5 Logical value
17
8.1.6 Real value. . .
.................................. 18
8.1.7 String value .
1
20
8.1.8 Enumeration value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
. Aggregation values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
82
21
83 . Simple instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
. Type instance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
84
22
85 . Select instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
. Enumeration instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
86
23
87 . Entity instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
Attributes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.7.1
26
8.7.2 Supertypes and subtypes . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
88 . Constant instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
89 . Schema data instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
8.10 Model display. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
............................... 30
9 Abstract test case specification
30
91 . Context .
......................................
31
92 . Parameters
............................... 31
9.2.1 Formal parameter
............................... 32
9.2.2 Actual parameter
32
. Testcase .
93
.................................... 33
94 . Test objective.
.................................. 34
9.4.1 Test purpose
................................. 34
Test reference.
9.4.2
.................................. 34
9.4.3 Test criteria.
35
9.4.4 Test notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
.
95 Test realization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
10 Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . .
111

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@IS0
ISO/TR 1030342:1997(E)
36
..............................
10.1 Schema instance interface
36
...................................
Schema reference
10.2
37
...............................
10.3 Context data references
38
.....................................
11 Scope and visibility
38
......................................
11.1 Scope rules
39
....................................
11.2 Visibility rules
39
...........................
11.2.1 General rules of visibility
.................. 40
11.2.2 Named data type identifier visibility rules
41
..................................
11.3 Explicit item rules
42
.................................
11.3.1 Alias statement
42
....................................
11.3.2 Attribute
42
....................................
11.3.3 Constant
11.3.4 Constant instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
42
.....................................
11.3.5 Context
43
......................................
11.3.6 Entity
43
.................................
11.3.7 Entity instance
11.3.8 Enumeration item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
44
.............................
11.3.9 Enumeration instance
44
Function .
11.3.10
11.3.11 Model. 44
44
...................................
11.3.12 Parameter.
45
...................................
Procedure.
11.3.13
45
................................
11.3.14 Query expression
45
...............................
Repeat statement
11.3.15
45
...................................
11.3.16 Rule label.
11.3.17 Schema data instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
11.3.18 Select instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Simple instance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
11.3.19
46
11.3.20 Testcase .
47
Type .
11.3.21
47
.................................
11.3.22 Type instance
47
...................................
11.3.23 Type label
47
Variable .
11.3.24
48
.........................
12 Mapping from EXPRESS to EXPRESS-I
........................... 48
Mapping of EXPRESS schema
12.1
49
.........................
12.1.1 Mapping of use and reference
..................... 50
12.2 Mapping of EXPRESS simple data types
51
.........................
12.3 Mapping of aggregation data types
52
.....................
12.4 Mapping of EXPRESS defined data type
..................... 52
12.5 Mapping of EXPRESS enumeration type
53
.........................
12.6 Mapping of EXPRESS select type
53
...............................
12.6.1 Simple select case
53
..............................
12.6.2 Complex select case
54
..........................
12.7 Mapping of EXPRESS constant

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ISO/TR 10303=12:1997(E)
@IS0
55
............................
12.8 Mapping of EXPRESS entity
55
......................
12.9 Mapping of EXPRESS entity attributes
............................... 56
Explicit attribute.
12.9.1
56
........................
12.9.2 Derived and inverse attributes
57
.......................
12.9.3 Attribute with a simple domain.
....................... 58
Attribute with an entity domain
12.9.4
............ 59
12.9.5 Attribute with a type, select or enumeration domain
60
........................
12.10 Mapping of supertypes and subtypes
....................... 63
12.10.1 Mapping of redeclared attributes
Annexes
65
............................
A Syntax description of EXPRESS-I
65
Al . Tokens .
65
Keywords .
A.l.l
68
................................
A.1.2 Character classes
69
...................................
A2 . Lexical elements
69
A.2.1 Remarks .
70
................................
A3 . Interpreted identifiers
70
....................................
A.4 Grammar rules
77
................................
A5 Cross reference listing
................ 88
B Protocol implementation conformance statement (PICS)
88
............................
Bl . EXPRESS-I language parser
89
..............................
C Information object registration
90
...............................
D Language specification syntax
90
...........................
D.1 The syntax of the specification
.............................. 91
D.2 Special character notation
93
.....................................
E Example test cases
93
. Test case 1 .
El
95
......................................
E2 . Test case 2
96
. Tcstxase3 .
E3
97
......................................
E4 . Test case 4
100
.........................................
F Usage notes
100
..............................
Fl . EXPRESS data examples
100
..................................
F2 . Abstract test cases
101
.....................................
Object bases
F3 .
101
......................................
F.3.1 Input
101
output .
F.3.2
101
..................................
F.3.3 Code testing
102
...........................
F4 . Non-EXPRESS data examples
103
....................................
G Technical discussions
103
..................................
. Abstract test cases
Gl
............................ 103
G2 . Relationship with EXPRESS
104
...................................
G3 . Object references
104
.....................................
. Aggregations
G4
104
...................................
G5 . Stringvalues.
V

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@IS0
ISO/TR 10303-12:1997(E)
............................ 105
G6 Model testing and validation
105
.......................
G-7 . Enhancement of test case capabilities
........................... 105
G8 . Compatibility with EXPRESS
...................................... 105
Trial Usage
G9 .
106
.................................
G.10 Alphabet extensions
106
.................................
G.ll Supertype mapping
............................ 107
G.12 CD ballot comments - 1995
107
...............................
G.12.1 Test case support
107
...........................
G.12.2 Complex entity instances
................................. 108
G.12.3 Type instances
109
........................................
H Bibliography
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .llO
Figures
1 The major elements of the EXPRESS-I language . . . . . . . . . . . . . . . . . . . . . xv
Tables
10
EXPRESS-I and EXPRESS . . . . . . . . . . . . . . . . . . . .
1 Keywords common to
............................. 10
2 Additional EXPRESS-I keywords
....................... 11
3 The EXPRESS-I use of EXPRESS operators
....................... 11
4 The EXPRESS-I use of EXPRESS constants
........................ 11
5 The EXPRESS-I use of EXPRESS functions
....................... 12
6 The EXPRESS-I use of EXPRESS procedures
..................... 12
7 Symbols common to EXPRESS-I and EXPRESS
12
8 Additional EXPRESS-I symbols .
..................... 38
9 Scope and identifier defining EXPRESS-I items
......... 39
10 Scope and identifier defining EXPRESS items utilisecl by EXPRESS-I
................................. 41
11 Scope and visibility rules
............... 13
12 Summary ovcrvicw of EXPRI3S t)o ESI’RESS-I mnppilgs
.............................. 49
13 Overview of SCHEMA mapping.
51
Simple type mapping. .
14
................................. 51
15 Mappingof AGGREGATES
55
...............................
16 Overview of ENTITYmapping
..................... 61
17 Overview of SUPERTYPE and SUBTYPE mapping
vi

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@IS0 ISO/TR 10303-12:1997(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of national
standards bodies (IS0 member bodies). The work of preparing International Standards is nor-
mally carried out through IS0 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. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
The main task of technical committees is to prepare International Standards, but in exceptional
circumstances a technical committee may propose the publication of a Technical Report of one
of the following types:
- type 1, when the required support cannot be obtained for the publication of an Interna-
tional Standard, despite repeated eforts;
- type 2, when the subject is still under technical development or where for any other
reason there is the future but not immediate possibility of an agreement on an International
Standard;
- type 3, when a technical committee has collected data of a different kind from that which
is normally published as an International Standard (“state of the art”, for example).
Technical reports of types 1 and 2 are subject to review within three years of publication, to
decide whether they can be transformed into International Standards. Technical reports of type
3 do not necessarily have to be reviewed until the data they provide are considered to be no
longer valid or useful.
ISO/TR 10303-12, which is a Technical Report of type 2, was prepared by Technical Committee
ISO/TC 184, Industrial automation systems and integration, Subcommittee SC4, Industrial
data.
There is an urgent need for guidance on how EXPRESS can be used to represent data so that it
is ‘human’ interpretable. This need is supported by the importance of involving domain experts
in the development of industrial data standards and in the development of abstract test cases
that can be used to verify conformance to such standards.
This document is being issued in the Technical Report (type 2) series of publications (according
to subclause G.3.2.2 of part 1 of the ISO/IEC Directives as a ‘prospective standard for provisional
application’ in the field of EXPRESS information modeling as there is an urgent need for guidance
on how standards in this field should be used to meet an identified need.
This document is not to be regarded as an ‘International Standard’. It is proposed for provisional
application so that experience of its use in practice may be gathered. Comments on the content
of this document should be sent to the IS0 Central Secretariat.
A review of this Technical Report (type 2) will be carried out not later than three years af-
ter its publication with the options of: extension for another three years; conversion into an
International Standard; or withdrawal.
vii

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@IS0
ISO/TR 10303-12:1997(E)
IS0 10303 consists of the following parts under the general title Industrial automation systems
and integration - Product data representation and exchange:
-
Part 1, Overview and fundamental principles;
-
Part 11, Description methods: The EXPRESS language reference manual;
-
Part 12, Description method: The EXPRESS-I language reference manual;
-
Part 21, Implementation methods: Clear text encoding of the exchange structure;
-
Part 22, Implementation method: Standard data access interface specification;
-
Part 23, Implementation method: C++ language binding to the standard data access
interface;
-
Part 24, Implementation method: C language binding to the standard data access inter-
face;
-
Part 26, Implementation method: Interface definition language binding to the standard
data access interface;
-
Part 31, Conformance testing methodology and framework: General concepts;
-
Part 32, Conformance testing methodology and framework: Requirements on testing
laboratories and clients;
-
Part 33, Conformance testing methodology and framework: Structure and use of abstract
test suites;
-
Part 34, Conformance testing methodology and framework: Abstract test methods;
-
Part 35, Conformance testing n~etl~odology ad fm~~~ework: Abstmct test udhcls fur
standard data access interface implementations;
Fundamentals of product description and support;
- Part 41, Integrated generic resources:
Geometric and topological representation;
- Part 42, Integrated generic resources:
- Part 43, Integrated generic resources: Representation structures;
Product structure configuration;
- Part 44, Integrated generic resources:
- Part 45, Integrated generic resource: Materials;
- Part 46, Integrated generic resources: Visual presentation;
- Part 47, Integrated generic resource: Shape variation tolerances;
. . .
Vlll

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ISO/TR 10303-12:1997(E)
@IS0
Process structure and properties;
- Part 49, Integrated generic resource:
- Part 101, Integrated application resource: Draughting;
- Part 104, Integrated application resource: Finite element analysis;
- Part 105, Integrated application resource: Kinematics;
- Part 106, Integrated application resource: Building construction core model;
- Part 201, Application protocol: Explicit draughting;
- Part 202, Application protocol: Associative draughting;
- Part 203, Application protocol: Configuration controlled design;
- Part 204, Application protocol: Mechanical design using boundary representation;
- Part 205, Application protocol: Mechanical design using surface representation;
- Part 207, Application protocol: Sheet metal die planning and design;
- Part 208, Application protocol: Life cycle management - Change process;
- Part 209, Application protocol: Composite and metallic structural analysis and related
design;
Electronic assembly, interconnect, and packaging design;
- Part 210, Application protocol:
-
Part 212, Application protocol: Electrotechnical design and installation;
-
Part 213, Application protocol: Numerical control process plans for rnachincd pwts;
-
Core data for automotive mechanical design;
Part 214, Application protocol:
-
Part 215, Application protocol: Ship arrangement;
-
Part 216, Application protocol: Ship moulded forms;
Ship piping;
- Part 217, Application protocol:
- Part 218, Application protocol: Ship structures;
-
Process planning, manufacture, and assembly of layered
Part 220, Application protocol:
electronic products;
-
Part 221, Application protocol: Functional data and their schematic representation for
process plant;
1x

---------------------- Page: 9 ----------------------
ISO/TR 10303=12:1997(E)
@
- Part 222, Application protocol: Exchange of product data for composite structures;
-
tT1
Part 223, Application protocol: Exchange of design and manufacturing product info]
tion for cast parts;
Mechanical product definition for process plans using
- Part 224, Application protocol:
mechanical feature;
- Part 225, Application protocol: Building elements using explicit shape representation;
- Part 226, Application protocol: Ship mechanical systems;
- Part 227, Application protocol: Plant spatial configuration;
Heating, ventilation, and air condi-
- Part 228, Application protocol: Building services:
t ioning;
- Part 229, Application protocol:. Exchange of design and manufacturing product informa-
tion for forged parts;
- Part 230, Application protocol: Building structural frame: Steelwork;
- Part 231, Application protocol: Process engineering data: Process design and process
specificat ion of major equipment ;
- Part 232, Application Protocol: Technical data package;
- Part 301, Abstract test suite: Explicit draughting;
- Part 302, Abstract test suite: Associative draughting;
- Part 303, Abstract test suite: Configuration co~~t~ollal tlcsign;
-
Part 304, Abstract test suite: Mechanical design using boundary representation;
- Part 305, Abstract test suite: Mechanical design using surface representation;
Part 307, Abstract test suite: Sheet metal die planning and design;
Part 308, Abstract test suite: Life cycle management - Change process;
- Part 309, Abstract test suite: Composite and metallic structural analysis and related
design;
- Part 310, Abstract test suite: Electronic assembly, interconnect, and packaging design;
- Part 312, Abstract test suite: Electrotechnical design and installation;
X

---------------------- Page: 10 ----------------------
@IS0 ISO/TR 10303-12:1997(E)
-
Part 313, Abstract test suite: Numerical control process plans for machined parts;
-
Part 314, Abstract test suite: Core data for automotive mechanical design;
- Part 315, Abstract test suite: Ship arrangement;
-
Part 316, Abstract test suite: Ship moulded forms;
-
Part 317, Abstract test suite: Ship piping;
- Part 318, Abstract test suite: Ship structures;
-
Part 320, Abstract test suite: Process planning, manufacture, and assembly of layered
electronic products;
-
Part 321, Abstract test suite: Functional data and their schematic representation for
process plant;
-
Part 322, Abstract test suite: Exchange of product data for composite structures;
-
Part 323, Abstract test suite: Exchange of design and manufacturing product information
for cast parts;
Mechanical product definition for process plans using
- Part 324, Abstract test suite:
mechani cal feat ures;
- Part bstract test suite: Building elements using explicit shape representation;
325, A
- Part 326, A bstract test suite: Ship mechanical systems;
- Pa,rt bstract test suite: Pl:l nt spatial configure t,ion;
327, A
bstract test suite: Building services: Heating, ventilation, and air condition-
- Part 328, A
ing;
-
Part 329, Abstract test suite: Exchange of design and manufacturing product information
for forged parts;
-
Part 330, Abstract test suite: Building structural frame: Steelwork;
- Part 331, Abstract test suite: Process engineering data: Process &sign and process
specificat ion of major equipment;
-
Part 332, Abstract test suite: Technical data package;
-
Part 501, Application interpreted construct: Edge-based wireframe;
xi

---------------------- Page: 11 ----------------------
@IS0
ISO/TR 10303-12:1997(E)
Shell-based wireframe;
- Part 502, Application interpreted construct:
Geometrically bounded 2D wireframe;
Part 503, Application interpreted construct:
Draughting annotation;
- Part 504, Application interpreted construct:
Drawing structure and administration;
- Part 505, Application interpreted construct:
Draught ing elements;
- Part 506, Application interpreted construct:
Geometrically bounded surface;
- Part 507, Application interpreted construct:
Non-manifold surface;
- Part 508, Application interpreted construct:
Manifold surface;
- Part 509, Application interpreted construct:
Geometrically bounded wireframe;
- Part 510, Application interpreted construct:
- Part 511, Application interpreted construct: Topologically bounded surface;
- Part 512, Application interpreted construct: Faceted boundary representation;
- Part 513, Application interpreted construct: Elementary boundary representation;
- Part 514, Application interpreted construct: Advanced boundary representation;
Constructive solid geometry;
- Part 515, Application interpreted construct:
Mechanical design gcome t ric present at ion;
- Part 517, Application interpreted construct:
Mrtclxmical design shadctl wpwsmt a t im.
- Part 518, Application interpreted constrwk
The structure of this International Standard is described in IS0 10303-l. The numbering of the
parts of this International Standard reflects its structure:
- Parts 11 to 12 specify the description methods,
- Parts 21 to 26 specify the implementation methods,
- Parts 31 to 35 specify the conformance testing methodology and framework,
- Parts 41 to 49 specify the integrated generic resources,
- Parts 101 to 106 specify the integrated application resources,
- Parts 201 to 232 specify the application protocols,
- Parts 301 to 332 specify the abstract test suites, and
xii

---------------------- Page: 12 ----------------------
@IS0 ISO/TR 10303-12:1997(E)
Parts 501 to 518 specify the application interpreted constructs.
Should further parts of IS0 10303 be published, they will follow the same numbering pattern.
Annexes A, B, C and D are an integral part of this part of IS0 10303. Annexes E, F, G and H
are for information only.
. . .
x111

---------------------- Page: 13 ----------------------
@IS0
ISO/TR 10303=-12:1997(E)
Introduction
IS0 10303 is an International Standard for the computer-interpretable representation and ex-
change of product data. The objective is to provide a neutral mechanism capable of describing
product data throughout the life cycle of a product independent from any particular system.
The nature of this description makes it suitable not only for neutral file exchange, but also as a
basis for implementing and sharing product databases and archiving.
This International Standard is organized as a series of parts, each published separately. The
parts of IS0 10303 fall into one of the following series: description methods, integrated resources,
application interpreted constructs, application protocols, abstract test suites, implementation
methods, and conformance testing. The series are described in IS0 10303-l. This part of
IS0 10303 is a member of the description methods series.
This part of IS0 10303 specifies the elements of the EXPRESS-I language. Each element of the
Simple elements are introduced first,
language is presented in its own context with examples.
then more complex ideas are presented in an incremental manner.
Language Overview
EXPRESS-I is the name of a formal data representation and abstract test case specification
language. It may be used to exemplify the information requirements of other parts of this
International Standard and is a companion to the EXPRESS and EXPRESS-G languages. It is
based on a number of design goals among which are:
-
The size and complexity of IS0 10303 demands that the language be parsable by both
computers and humans. Expressing elements of IS0 10303 in a less formal manner would
eliminate the possibility of employing computer automation in checking for inconsistencies
in presentation or specification.
-
Focus on the display of the realisation of the properties of entities, which represent objects
of interest. The definition of an entity is in terms of its propc&x, dkA ax clmxtuixd
by specification of a domain and the constraints on that domain.
- Avoid, as far as possible, specific implementation views.
-
Provide a means of displaying small populations of EXPRESS schemas.
-
Provide a means of supporting the specification of abstract test suites for information
model processors.
In EXPRESS-I, entity instances are represented in terms of attribute values: the traits or charac-
teristics considered important for use and understanding. These attributes have a representation
which might be a simple data type (such as integer) or another entity type. A geometric point
might be defined in terms of
...