ISO/IEC 15476-3:2006

Information technology - CDIF semantic metamodel - Part 3: Data definitions

ISO/IEC 15476-3:2006 explains the Data definitions subject area of the CDIF semantic metamodel, that defines the primitive data types and the objects which are used for structured data. The CDIF semantic metamodel is used to ensure that the information transferred by tools communicating using CDIF is expressed with an agreed meaning. This subject area contains meta-objects that are used as the basis of the data components of other subject area standards, and also meta-relationships and meta-attributes that are applicable to all data-related meta-objects. ISO/IEC 15476-3:2006 is intended to be used by anyone wishing to understand and/or use CDIF. It provides a definition of a single subject area of the CDIF semantic metamodel. It is suitable for: Those evaluating CDIF; Those who wish to understand the principles and concepts of a CDIF transfer; and Those developing importers and exporters.

Technologies de l'information — Métamodèle sémantique CDIF — Partie 3: Definitions de données

General Information

• Status: Published
• Publication Date: 08-Jan-2006
• ICS: 35.080 - Software
• Technical Committee: ISO/IEC JTC 1/SC 7 - Software and systems engineering
• Drafting Committee: ISO/IEC JTC 1/SC 7/WG 19 - Techniques for Specifying IT Systems
• Current Stage: 9093 - International Standard confirmed
• Start Date: 03-Jan-2019
• Completion Date: 30-Oct-2025

Overview

ISO/IEC 15476-3:2006 - "Information technology - CDIF semantic metamodel - Part 3: Data definitions" defines the data definitions subject area of the CDIF (CASE Data Interchange Format) semantic metamodel. It documents the primitive data types, structured-data objects, meta-objects, meta-attributes and meta-relationships used to express data with an agreed meaning when tools exchange information using CDIF. The standard supports consistent interpretation of transferred data and serves as a foundation for data components in other CDIF subject-area standards.

Key Topics

• Primitive and complex DataTypes: definitions for basic, exact/approximate numeric, string, binary, temporal, complex and void/unknown types.
• Structured data objects: meta-entities for aggregates, arrays, pointers, qualifiers and refined/qualified data types.
• Value domains and constraints: ValueDomain, ValueDomainRange, ValueDomainEnumeration, ValueDomainRule and ValueDomainGroup to constrain permissible values.
• Units and measurement: Units associated with numeric types to support semantic clarity of measured quantities.
• Computable values and formats: specification of computable languages and formats for representing computable values (e.g., functions or expressions used in constraints).
• General structuring mechanism: DefinitionObject / ComponentObject patterns, meta-relationships and attribution models to reuse and share data definitions.
• Conformance rules: input, output and round‑trip conformance types to guide implementers and ensure interoperable exchanges.
• Documentation artifacts: meta-entity and meta-relationship definitions, diagrams and tables to aid implementers.

Applications and Who Uses It

ISO/IEC 15476-3:2006 is intended for:

• Tool vendors and integrators developing CDIF importers/exporters to ensure semantic interoperability.
• System architects and data modelers who need well-defined primitive types and structured-data building blocks for tool-to-tool exchanges.
• Evaluators and standards adopters assessing CDIF suitability for enterprise or engineering toolchains.
• Software engineers implementing data conversion, model transformation and round-trip synchronization between CASE tools.

Practical uses include exchanging model and metadata between CASE tools, defining portable data schemas, validating transferred values against value domains, and ensuring units and numeric semantics are preserved.

Related Standards

• ISO/IEC 15476 (CDIF family) - other parts of the CDIF semantic metamodel
• Normative references cited in the standard include ISO/IEC 15474-1 and ISO/IEC 13238-1 (as referenced in the document)

Keywords: ISO/IEC 15476-3, CDIF semantic metamodel, data definitions, primitive data types, value domain, data typing, conformance, importers exporters, structured data, units.

Standards Content (Sample)

INTERNATIONAL ISO/IEC
STANDARD 15476-3
First edition
2006-01-01
Information technology — CDIF semantic
metamodel —
Part 3:
Data definitions
Technologies de l'information — Métamodèle sémantique CDIF —
Partie 3: Definition de données

Reference number
©
ISO/IEC 2006
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ii © ISO/IEC 2006 – All rights reserved

Contents
1 Scope.1
2 Conformance.2
2.1 General.2
2.2 Input conformance.2
2.3 Output conformance.2
2.4 Round-trip conformance.3
3 Normative references.3
4 Terms and definitions.4
4.1 From other International Standards .4
4.1.1 ISO/IEC 15474-1.4
4.1.2 ISO/IEC 13238-1.4
4.1.3 For this International Standard .4
5 Symbols (and abbreviated terms).5
5.1 Naming, diagramming and definition conventions .5
5.2 Abbreviations.5
6 Data definition subject area overview .5
6.1 Introduction.5
6.2 Data Typing.5
6.3 The General Structuring Mechanism.5
6.3.1 Introduction.5
6.3.2 Meta-entities and Meta-relationships .5
6.3.3 DefinitionObject and ComponentObject .7
6.4 Alternate Decompositions.8
6.5 Pointers and Arrays.10
6.6 Data Types.10
6.7 Constraining Data Type and Attribute Values .11
6.8 Units for Numeric DataTypes.12
6.9 Void and Unknown Data Types.13
6.10 Computable Languages.13
6.11 Formats for Computable Values .13
6.12 Diagrams.16
7 Data definitions subject area summary.21
7.1 AttributableMetaObject classification hierarchy .21
7.2 MetaEntity summary.23
7.3 MetaRelationship summary.37
8 Data definitions subject area specification.39
8.1 Introduction.39
8.1.1 Subject area definition.39
8.2 Meta-entity definitions.39
8.2.1 AggregateDataType.39
8.2.2 ApproximateNumericType.40
8.2.3 ArrayQualifier.41
8.2.4 Attribute.42
8.2.5 BasicDataType.42
8.2.6 BinaryCodedDecimalType.43
8.2.7 BinaryType.43
8.2.8 BooleanType.44
8.2.9 BoundedArrayQualifier.44
8.2.10 CartesianComplexType.45
© ISO/IEC 2006 – All rights reserved iii

8.2.11 ComplexType.46
8.2.12 DataType.47
8.2.13 DateType.48
8.2.14 DayTimeIntervalType.49
8.2.15 DefinitionObject.49
8.2.16 EnumerationType.49
8.2.17 ExactNumericType.50
8.2.18 FixedDecimalType.51
8.2.19 FixedLengthBinaryType.52
8.2.20 FixedLengthStringType.54
8.2.21 IntegerType.55
8.2.22 MagnitudeType.55
8.2.23 MoneyType.56
8.2.24 NLFixedLengthStringType.57
8.2.25 NLVariableLengthStringType.58
8.2.26 NumericType.59
8.2.27 PackedDecimalType.59
8.2.28 PointerQualifier.60
8.2.29 PolarComplexType.60
8.2.30 QualifiedDataType.62
8.2.31 Qualifier.62
8.2.32 RefinedDataType.63
8.2.33 SerialType.63
8.2.34 StringType.65
8.2.35 TemporalType.66
8.2.36 TimeIntervalType.66
8.2.37 TimeStampType.67
8.2.38 TimeType.68
8.2.39 UnboundedArrayQualifier.69
8.2.40 Unit.70
8.2.41 ValueDomain.74
8.2.42 ValueDomainEnumeration.75
8.2.43 ValueDomainGroup.76
8.4.44 ValueDomainProcedure.77
8.2.45 ValueDomainRange.78
8.2.46 ValueDomainRule.80
8.2.47 VariableLengthBinaryType.81
8.2.48 VariableLengthStringType.82
8.2.49 VoidType.84
8.2.50 YearMonthIntervalType.84
8.3 Meta-relationship definitions.85
7.3.1 ArrayQualifier.HasType.DataType.85
7.3.2 DataType.TakesValueFrom.ValueDomain.85
7.3.3 NumericType.IsMeasuredIn.Unit.86
8.3.1 RootEntity.IsRelatedTo. RootEntity.86
8.3.2 QualifiedDataType.IsQualificationOf.DataType .86
8.3.3 QualifiedDataType.IsQualifiedBy.Qualifier.87
8.3.4 RefinedDataType.IsRefinementOf.DataType.87
8.3.5 ValueDomainGroup.Contains.ValueDomain.88

Table of Illustrations
Figure 1 − CDIF family of International Standards . 1
Figure 2 − Part of general Structuring Mechanism for data definitions subject area. 6
Figure 3 − Meta-model fragment for simple attribution with defined DataTypes. 6
Figure 4 − Instance Diagram showing simple attribution with defined DataTypes. 7
iv © ISO/IEC 2006 – All rights reserved

Figure 5 − Instance diagram of attributes sharing the same structured definition. 8
Figure 6 − Instance diagram of alternate Data Structures. 9
Figure 7 − Concepts of shared attribute values and definitions. 10
Figure 8 − Usage of ValueDomainGroup and ValueDomain. 12
Figure 9 − Data Definition Subject Area - Main Diagram. 16
Figure 10 . 17
Figure 11 − MagnitudeType Subtypes . 18
Figure 12 − NumericType Subtypes. 19
Figure 13 − Subtypes and meta-relationships for Qualifier. 20
Figure 14 − ValueDomainGroup and related meta-entities .20
Table of Tables
Table 1 − Formats for Computable Values. 13
Table 2 − Notation Used for Computable Values . 15
Table 3 − Function Values for Computable Values . 15
© ISO/IEC 2006 – All rights reserved v

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national 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 and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC 15476-3 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 7, Software and system engineering.
ISO/IEC 15476 consists of the following parts, under the general title Information technology — CDIF
semantic metamodel:
— Part 1: Foundation
— Part 2: Common
— Part 3: Data definitions
— Part 4: Data models
— Part 5: Data flow models
— Part 6: State/event models
vi © ISO/IEC 2006 – All rights reserved

Introduction
This International Standard will assist the vendors and users of modelling tools and meta-data repositories in
developing mechanisms for interchanging information. This International Standard specifies an element of a family
of related standards. When used together, these International Standards specify a mechanism for transferring
information between tools.
ISO/IEC 15474-1:2002, Information technology - CDIF framework - Part 1: Overview and ISO/IEC 15474-2,
Information technology - CDIF framework - Part 2: Modelling and extensibility should be read first when initially
exploring CDIF. The first explains the overall CDIF architecture and how the family of standards fits together. The
second explains the scope, and modelling approach in CDIF. The CDIF meta-metamodel and extensibility
mechanism are also defined in that document.
This International Standard explains the data definitions subject area of the CDIF semantic metamodel, which
defines the primitive data types and the objects which are used for structured data. The CDIF semantic metamodel
is used to ensure that the information transferred by tools communicating using CDIF is expressed with an agreed
meaning.
This International Standard has been developed with the wide support and participation of vendors, users,
academia and government involved in or familiar with the CASE industry, its products and the general requirements
associated with interchanging information between these products.
This document is organized into the following Clauses:
⎯ Clause 1 to 5 are prescribed ISO/IEC Clauses.
⎯ Clause 6: Subject area overview:
This Clause gives an overview of the coverage of this subject area.
⎯ Clause 7: Subject area summary:
This Clause gives an overview of the content of this subject area.
⎯ Clause 8: Subject area specification:
This Clause gives the formal specification of all the objects defined in the subject area, and the formal
reference to those used, but not defined in the subject area.
This document is intended to be used by anyone wishing to understand and/or use CDIF. This document provides
a definition of a single subject area of the CDIF semantic metamodel. It is suitable for:
⎯ Those evaluating CDIF;
⎯ Those who wish to understand the principles and concepts of a CDIF transfer; and
⎯ Those developing importers and exporters.
This document, ISO/IEC 15474-1:2002, Information technology - CDIF framework - Part 1: Overview, and the
framework document ISO/IEC 15474-2:2002, Information technology - CDIF framework - Part 2: Modelling and
extensibility, should be read first when initially exploring CDIF and before attempting to read other documents in the
CDIF family of International Standards.
© ISO/IEC 2006 – All rights reserved vii

While there are no specific prerequisites for reading this document, it will be helpful for the reader to have familiarity
with the following:
⎯ Entity-Relationship-Attribute modelling;
⎯ Modelling (CASE) tools;
⎯ Information repositories;
⎯ Data dictionaries and;
⎯ Multiple meta-layer modelling.
viii © ISO/IEC 2006 – All rights reserved

INTERNATIONAL STANDARD ISO/IEC 15476-3:2006(E)

Information technology — CDIF semantic metamodel —

Part 3:
Data definitions
1 Scope
The CDIF family of International Standards is primarily designed to be used as a description of a mechanism for
transferring information between modelling tools. It facilitates a successful transfer when the authors of the
importing and exporting tools have nothing in common except an agreement to conform to CDIF. The language that
is defined for the transfer format also has applicability as a general language for import/export from repositories.
The CDIF semantic metamodel defined for CASE also has applicability as the basis of standard definitions for use
in repositories.
The International Standards which form the complete family of CDIF standards are documented in ISO/IEC 15474-
1:2002, Information technology — CDIF framework — Part 1: Overview. These standards cover the overall
framework, the transfer format and the CDIF semantic metamodel.

15474 CDIF framework
Part 1 : Overview Part 2 : Modelling and extensibility

15476 CDIF semantic metamodel 15475 CDIF transfer format

Part 1 : Foundation Part 1 : General rules for

Part 2 : Common
syntaxes and encodings
Part 3 : Data definitions
Part 2 : Syntax SYNTAX.1
Part 4 : Data models
Part 5 : Data flow models Part 3 : Encoding ENCODING.1

Part 6 : State/event models
Part n : .
Part n : .
Figure 1 − CDIF family of International Standards
The diagram in Figure 1 depicts the various International Standards that comprise the CDIF family of standards.
The shaded box depicts this International Standard and its position in the CDIF family of standards.
© ISO/IEC 2006 – All rights reserved 1

This International Standard defines the Data Definition Subject Area of the CDIF semantic metamodel. This subject
area contains meta-objects that are used as the basis of the data components of other subject area standards, and
also meta-relationships and meta-attributes that are applicable to all data-related meta-objects.
2 Conformance
2.1  General
A product is fully standards conformant to a CDIF subject area standard if and only if it is input-conformant, output-
conformant and round-trip conformant to each and every MetaEntity, MetaRelationship, MetaAttribute, and
AttributableMetaObject which is defined and/or used in that standard, and it is also CDIF architecture conformant. A
product may be partially input-conformant, and/or partially output-conformant, and/or partially round-trip conformant
to a CDIF subject area standard.
2.2  Input conformance
Input conformance for a specific MetaEntity, MetaRelationship, MetaAttribute, or AttributableMetaObject (short:
CollectableMetaObject) is determined by applying the following test:
A set of meta-data containing all meanings and structures standardized by a CDIF subject area is imported by the
product under test. Then the meta-data which has arrived in the product is examined. The following options exist
for the relation between the input (CDIF) meta-data and the imported (product) meta-data:
For a specific CollectableMetaObject:
1 The product is input conformant if each instance of the specific CollectableMetaObject has arrived in the product
without change of meaning or structure. If the CollectableMetaObject is a meta-entity or meta-relationship, its
structural relationships to other CollectableMetaObjects have been preserved. If the CollectableMetaObject is a
meta-attribute, the value of the meta-attribute has been preserved.
2 The product is input morphing conformant if each instance of the specific CollectableMetaObject has arrived in
the product, but with some changes in meaning or structure. If the CollectableMetaObject is a meta-attribute,
the value(s) for some instances of the meta-attribute have changed.
3 The product is not input conformant for that CollectableMetaObject if neither of the previous tests is satisfied.
2.3  Output conformance
Output conformance for a specific CollectableMetaObject is determined by applying the following test:
For the product being tested, a set of meta-data that includes all possible meanings and structures representable in
that product is exported. Then the meta-data that has been exported is examined. The following options exist for
the relation between the product's meta-data and the exported (CDIF) meta-data:
For a specific CollectableMetaObject:
1 The product is output conformant if all of the meaning and structure for the specific CollectableMetaObject has
been represented as meta-data in the product and has been exported as one or more instances of that
CollectableMetaObject. If the CollectableMetaObject is a meta-attribute, the correct value of the meta-attribute
has been exported.
2 The product is output morphing conformant if each instance of meta-data in the product that has the same
meaning and structure as the CollectableMetaObject has been exported, but some instances have been
exported as a different CollectableMetaObject or some of the meaning and structure has been changed.
2 © ISO/IEC 2006 – All rights reserved

3 If the product does not represent the meaning and structure associated with the CollectableMetaObject, output
conformance for that CollectableMetaObject is not applicable to the product.
4 In all other cases, the product is not output conformant for that CollectableMetaObject.
2.4  Round-trip conformance
Round-trip conformance for a specific CollectableMetaObject is determined by applying the following test:
A set of meta-data containing all meanings and structures standardized by a CDIF subject area is imported by the
product under test. Then the meta-data is exported again. The following options exist for the relation between the
input meta-data and the output meta-data:
For a specific CollectableMetaObject:
1 The product is round-trip conformant if the meaning and structure of each instance of the CollectableMetaObject
is preserved without changes during the round-trip. For a vendor to claim round-trip conformance, it is also
necessary for the tool to be able to perform create, read, update, and delete operations on the imported
(product) meta-data corresponding to the instances of the CollectableMetaObject.
2 The product is round-trip morphing conformant if each instance of the input CollectableMetaObject is preserved,
but with some changes in meaning and/or structure. If the CollectableMetaObject is a meta-entity or meta-
relationship, some of its instances' structural relationships to other CollectableMetaObjects have changed, or
some instances have been transformed into other CollectableMetaObjects, or instances of other
CollectableMetaObjects have been transformed into instances of the CollectableMetaObject. If the
CollectableMetaObject is a meta-attribute, the values of some instances of the meta-attribute have changed or
the domain of the meta-attribute has changed.
3 In all other cases, the product is not round-trip conformant for that CollectableMetaObject.
3 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 31-1:1992 Quantities and units – Part 1: Space and time
ISO 4217:2001, Codes for the representation of currencies and funds
ISO/IEC 9945-1:1996, Information technology – Portable Operating System Interface (POSIX) –Part 1: System
Application Program Interface (API) [C Language]
ISO/IEC 13238-1, Information technology - Data management export/import - Part 1: Standardization framework.
ISO/IEC 15474-1, Information technology — CDIF framework — Part 1: Overview
ISO/IEC 15474-2, Information technology — CDIF framework — Part 2: Modelling and extensibility
ISO/IEC 15476-1, Information technology — CDIF semantic metamodel — Part 1: Foundation
ISO/IEC 15476-2, Information technology — CDIF semantic metamodel — Part 2: Common
ISO/IEC 15476-4 Information technology — CDIF semantic metamodel — Part 4: Data models
CHARACTER SETS, IANA, available at
© ISO/IEC 2006 – All rights reserved 3

4 Terms and definitions
For the purposes of this document, the following definitions apply. Unless otherwise noted, the definitions are
specific to this International Standard.
4.1  From other International Standards
4.1.1 ISO/IEC 15474-1
This part of ISO/IEC 15476 makes use of the following terms defined in ISO/IEC 15474-1:
CDIF
CDIF family of standards
CDIF semantic metamodel
CDIF meta-metamodel
CDIF transfer
Instance
Meta-attribute
Meta-entity
Metamodel
Meta-object
Meta-relationship
Model
Subject area
Transfer
Transfer format
4.1.2 ISO/IEC 13238-1
This part of ISO/IEC 15476 makes use of the following terms from ISO/IEC 13238-1:
Exporter
Importer
4.1.3 For this International Standard
For the purpose of this part of ISO/IEC 15476 new terms are defined when introduced. Double quotes are used to
introduce new terms (e.g., "model layer")
4 © ISO/IEC 2006 – All rights reserved

5 Symbols (and abbreviated terms)
5.1  Naming, diagramming and definition conventions
Conventions for naming, diagramming, describing and defining meta-objects can be found in Clause 7 of the
framework document (ISO/IEC 15474-2:2002, Information technology - CDIF framework - Part 2: Modelling and
extensibility).
5.2   Abbreviations
The following abbreviation is used in this International Standard:
CDIF CASE Data Interchange Format (originally)
6 Data definition subject area overview
6.1 Introduction
The Data Definition Subject Area provides support for describing data objects and provides a data typing scheme.
It allows for simple and complex structures, array and pointer qualification and domain specification. The Data
Definition Subject Area diagrams are shown in Figure 9 through Figure 14.
6.2 Data Typing
A data type is described by one or more Attributes, and each of these Attributes may have a defined data type,
represented by the meta-entity DataType. This Subject Area does not cover the internal representation of
information within the basic data types; it only covers the concept of the type of information represented.
Figure 3 shows a fragment of the meta-model illustrating how data typing is represented. Figure 4 is an instance
diagram of the model elements in Figure 3. Note that in the instance diagrams, values of meta-attributes (usually
Name) are only given where they are required.
The data type of each Attribute is defined by relating it to the meta-entity DataType and its subtypes. These are
described in subclauses 6.8 to 6.11. In the instance diagrams, the most appropriate subtype of DataType is used.
The meta-attribute Name of the meta-entity Attribute allows a local name to be defined for the attribute. If no value
is given, then it is assumed that the name is the same as that of the underlying DataType. A default value for the
Attribute can be defined using the meta-attribute DefaultValue, as can the optionality, using the meta-attribute
IsOptional (The meta-attributes, DefaultValue and IsOptional, are defined in ISO/IEC 15476-4 Data models).
6.3 The General Structuring Mechanism
6.3.1 Introduction
Support for the decomposition and structuring of objects into other objects, and the reuse of definitions, is provided
by a general structuring mechanism. This mechanism is defined in ISO/IEC 15476-2:2002, Information Technology
- CDIF Semantic Metamodel - Part 2: Common, and is also used in other CDIF subject areas.
In this subject area DataTypes may be structured. Structuring of DataTypes is performed using the general
structuring mechanism because its definition may be used for several objects in different contexts.
6.3.2 Meta-entities and Meta-relationships
The general structuring mechanism used in this subject area makes use of the following meta-entities:
© ISO/IEC 2006 – All rights reserved 5

• ComponentObject
• DefinitionObject
and the following meta-relationships:
• DefinitionObject.Contains.ComponentObject
• ComponentObject.References.DefinitionObject.
Figure 2 shows the part of meta-model for the general structuring mechanism related to meta-entity DataType.
0:N References 0:1
Definition
Component
Object
Object
0:N 0:1
Contains
Attribute
DataType
Figure 2 − Part of general Structuring Mechanism for data definitions subject area

Figure 3 and Figure 4 show how the general structuring mechanism represent a hierarchical data structure. The
combination of the meta-relationship DefinitionObject.Contains.ComponentObject which is used for data structure
and the meta-relationship ComponentObject.References.DefinitionObject which is used for data declaration is
shown in Figure 3. The sample instance diagram is Figure 4. In this case, two data named Customer and Order
are defined. Both data definition have fixed length sting type named CustomerNumber.

Contains References
Aggregate
Attribute DataType
DataType
0:1 0:N 0:N 0:1
Figure 3 − Meta-model fragment for simple attribution with defined DataTypes

6 © ISO/IEC 2006 – All rights reserved

Aggregate Aggregate
DataType DataType
Customer Order
Contains Contains
Attribute Attribute
CustNo
References
References
FixedLength
StringType
Customer
Number
Figure 4 − Instance Diagram showing simple attribution with defined DataTypes
6.3.3 DefinitionObject and ComponentObject
DefinitionObject serves as an abstract supertype for all decomposition and structure definitions that may be reused.
A DefinitionObject represents the definition of a ComponentObject, using meta-relationship
ComponentObject.References.DefinitionObject. A DefinitionObject may contain ComponentObjects, using the
DefinitionObject.Contains.ComponentObject meta-relationship. The ComponentObjects contained in a
DefinitionObject represent the components of the definition.
Both ComponentObject and DefinitionObject represent abstract concepts and thus shall not be instantiated.
Instead, appropriate subtypes, provided by this or other subject areas, are used for instantiating data definitions.
A subtype of DefinitionObject may be referenced by any number of ComponentObjects indicating that all those
ComponentObjects share the same definition. For example, in Figure 5, Attributes a and b share the same
definition, AggregateDataType MyStruct.
Instances of the subtypes of ComponentObject are used to describe the structure of a deta described by a
DefinitionObject. There may be any number instances of ComponentObjects per instance of DefinitionObject. In
Figure 5, Attributes x and y comprise the structure of MyStruct.

© ISO/IEC 2006 – All rights reserved 7

Attribute
a
Aggregate
References
DataType
MyStruct
Attribute
References
Contains Contains
b
Attribute Attribute
x y
Figure 5 − Instance diagram of attributes sharing the same structured definition

For example, if a structure is built containing two components that share the same definition, the instance of
structured DefinitionObject will contain two distinct instances of ComponentObject which refer to the same shared
instance of the DefinitionObject.
The general structuring mechanism ensures that, for example, the instances of the components of one structured
Attribute are different from those of another structured Attribute even if both Attributes share the same instance of a
DataType.
6.4 Alternate Decompositions
This subject area supports alternate decompositions of DataTypes using the general structuring mechanism.
Decompositions may have one of two characteristics, represented by the meta-attribute Operator of the meta-entity
DefinitionObject. DataType is a subtype of DefinitionObject and thus inherits the meta-attribute Operator.
If the instance value of this meta-attribute is AND, this indicates that all instances of the all ComponentObjects
related to the instance of DefinitionObject using the instance of meta-relationship
DefinitionObject.Contains.ComponentObject are contained at the same time (i.e. inclusive).
For example, in Figure 6, the AggregateDataType instance Y1Def representing a data structure definition would set
the value of Operator to AND because it contains all the attributes concurrently.
The value XOR of the Operator meta-attribute specifies that the ComponentObject instances contained in the
DefinitionObject instance are exclusive alternates. This means that the object is decomposed into exactly one of
the ComponentObject instances but which one is not specified. An alternate decomposition leaves it open as to
which of the decompositions is to be used.
For example, in Figure 6, if an Attribute X has two decompositions into Attributes A, B and C, or into Attributes D
and E, a AggregateDataType XDef is created which is the definition of Attribute X, using the instance of meta-
relationship ComponentObject.References.DefinitionObject. AggregateDataType instance XDef has its meta-
8 © ISO/IEC 2006 – All rights reserved

attribute Operator set to XOR. There are two Attribute instances Y1 and Y2 which are contained in XDef using
meta-relationship DefinitionObject.Contains.ComponentObject instance, indicating that the AggregateDataType
has two possible structures. The Attribute instances Y1 and Y2 have AggregateDataType instances Y1Def and
Y2Def, using ComponentObject.References.DefinitionObject instance. Those AggregateDataTypes instances have
set their meta-attribute Operator to AND, indicating that all their components are contained and they do not
represent alternates. Note that if the Operator meta-attribute has a value of XOR, then the contained Attributes
instances do not actually exist as a part of the containing Attribute's structure, but are simply playing the role of a
grouping mechanism. Those AggregateDataType instances Y1Def and Y2Def contain Attribute instances A, B and
C, or D and E, respectively.
For example, the "C" programming language supports the union concept. In this case the AggregateDataType's
meta-attribute Operator would have the value XOR.
Attribute
X
References
Contains Contains
Aggregate
DataType
XDef
Operator: XOR
Attribute Attribute
Y1 Y2
References
References
Contains Contains Contains
Aggregate Aggregate
DataType DataType
Y1Def Y2Def
Operator: AND Operator: AND
Contains
Contains
Attribute Attribute Attribute Attribute Attribute
A B C D E
Figure 6 − Instance diagram of alternate Data Structures
© ISO/IEC 2006 – All rights reserved 9

The concepts of attributes, shared definitions and underlying types are illustrated in Figure 7.
Concept
...