ISO/TS 10303-28:2003

TECHNICAL ISO/TS
SPECIFICATION 10303-28
First edition
2003-08-01
Industrial automation systems and
integration — Product data
representation and exchange —
Part 28:
Implementation methods: XML
representations of EXPRESS schemas
and data
Systèmes d'automatisation industrielle et intégration — Représentation
et échange de données de produits —
Partie 28: Méthodes d'implémentation: représentations XML de
schémas et de données EXPRESS
Reference number
©
ISO 2003
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ii © ISO 2003 — All rights reserved

Content Page
Foreword.viii
Introduction.ix
1 Scope.1
2 Normative references.2
3 Terms, definitions, and abbreviations.3
3.1 Terms defined in ISO 10303-1.3
3.2 Other terms and definitions.3
3.3 Abbreviations.5
3.4 Terminology.5
4 Fundamental concepts, assumptions, and limitations.6
4.1 Early and late binding .6
4.2 Mapping between bindings .6
4.2.1 Use of Architectural forms .7
4.2.2 Use of XSLT.8
4.3 XML markup declaration sets and Document Type Declarations .9
4.4 XML names.9
4.4.1 Name restrictions in XML.9
4.4.2 Use of case in XML element type names .9
4.5 Use of ID, IDREF and the reftype XML attribute .9
4.6 Character coding limitations .10
5 Conformance.10
5.1 Conformance of an XML document .11
5.1.1 Binding conformance .11
5.1.2 Architectural conformance .11
5.1.3 XML document representation categories.11
5.2 Conformance of an XML document element.12
5.3 Conformance of a pre-processor .13
5.4 Conformance of a post-processor.13
5.5 Conformance of a markup declaration generator.13
6 Document level elements.13
6.1 The iso_10303_28 element .14
6.2 Document header information.14
6.2.1 The iso_10303_28_header element .14
6.2.2 The document_name element.14
6.2.3 The time_stamp element.15
6.2.4 The author element .15
6.2.5 The originating_organization element.15
6.2.6 The authorization element .15
6.2.7 The originating_system element.16
6.2.8 The preprocessor_version element .16
6.2.9 The purpose element.16
6.2.10 The documentation element .16
6.3 The schema_population element.16
6.4 EXPRESS schema descriptive information .18
6.4.1 The express_schema element .18
6.4.2 The schema_text element .19
6.4.3 The schema_decl element.19
6.5 Data descriptive information.19
6.5.1 The express_data element.19
6.5.2 The data_section_header element.20
6.6 Inter-XML document reference information.21
6.6.1 References to remote XML resources .21
6.6.2 Referencing a remote XML element .21
6.6.3 Including components in documents .22
7 Late-bound markup declarations for EXPRESS-defined data.24
7.1 Representation of a schema instance.25
7.2 Representation of an EXPRESS entity instance.26
7.2.1 Representation using the entity_instance element.26
7.2.2 Representation using entity_instance_as_group.27
7.3 Representation of EXPRESS attributes.28
7.3.1 Representation of EXPRESS mandatory explicit attributes.29
7.3.2 Representation of EXPRESS OPTIONAL explicit attributes.30
7.3.3 Representation of EXPRESS INVERSE attributes .30
7.3.4 Representation of DERIVEd attributes .30
7.3.5 Representation of redeclared attributes .31
7.3.6 Representation of explicit attributes redeclared as DERIVEd .31
7.3.7 Representation of attributes redeclared as INVERSE .31
7.4 Representation of EXPRESS attribute values.31
7.4.1 Representation of primitive data types .32
7.4.2 Representation of aggregate data types .34
7.4.3 Representation of defined data types.37
7.4.4 Representation of EXPRESS attribute values that are EXPRESS entity instance
references .39
8 EXPRESS-typed Early Binding (ETEB).41
8.1 Fundamental concepts and assumptions.41
8.1.1 Preconditions .41
8.1.2 EXPRESS entity referencing.41
8.1.3 Multiple supertypes .42
8.1.4 Unmapped EXPRESS concepts.43
8.1.5 Late binding architectural form .43
8.1.6 Inter-subtype constraints.43
8.2 XML markup declaration set.44
8.2.1 Element naming.44
8.2.2 Schema independent declarations.44
8.2.3 EXPRESS schema declaration .46
8.2.4 Defined data types .48
8.2.5 EXPRESS entity data type declarations .51
8.2.6 EXPRESS explicit attribute declarations .55
8.2.7 Subtypes and supertypes.59
8.2.8 Aggregate data types .63
iv © ISO 2003 — All rights reserved

8.2.9 Interface specifications .66
8.2.10 Constants.69
8.2.11 Derived attributes.70
8.2.12 Declaration set optimizations.70
8.3 Data encoding.70
8.3.1 Representation of EXPRESS entity instances .70
8.3.2 Representation of EXPRESS explicit attributes.71
8.3.3 Representation of DERIVEd attributes .71
8.3.4 Representation of EXPRESS attribute values .71
9 Object Serialization Early Binding (OSEB) .74
9.1 Fundamental Concepts and Assumptions .74
9.1.1 Preconditions .74
9.1.2 Unmapped EXPRESS concepts.74
9.2 OSEB element naming.75
9.2.1 Mapping EXPRESS identifiers to XML.75
9.2.2 Names resulting from EXPRESS named data types.75
9.3 EXPRESS schema-independent element types.76
9.3.1 Elements for simple types.76
9.3.2 Elements for aggregate types.78
9.3.3 The unset element.79
9.3.4 The uos element.79
9.3.5 The external identification elements.80
9.3.6 The spath element.80
9.4 XML declarations for EXPRESS named data types .81
9.4.1 EXPRESS ENUMERATION types .81
9.4.2 EXPRESS SELECT types.81
9.4.3 EXPRESS entity data types.82
9.4.4 EXPRESS non-constructed defined data types .86
9.5 XML declarations for EXPRESS attributes .88
9.5.1 Attribute naming.88
9.5.2 Explicit attributes.90
9.5.3 INVERSE attributes .90
9.5.4 DERIVEd attributes.91
9.5.5 Redeclared attributes .92
9.6 XML attribute types for EXPRESS attributes.92
9.6.1 NUMBER, REAL, INTEGER attributes.92
9.6.2 BOOLEAN attributes .93
9.6.3 LOGICAL attributes.93
9.6.4 STRING attributes.94
9.6.5 BINARY attributes .94
9.6.6 ENUMERATION-typed attributes.95
9.6.7 SELECT-typed attributes .95
9.6.8 EXPRESS entity instance-valued attributes .96
9.6.9 Attributes with non-constructed defined types.96
9.6.10 Attributes with aggregate data types .97
9.7 Creation of express_data content .99
9.7.1 Unit of serialization .99
9.7.2 Representation of EXPRESS entity instances .105
9.7.3 Representation of the unset element.106
9.8 Representation of EXPRESS attribute values.106
9.8.1 Representation of INTEGER values.106
9.8.2 Representation of REAL and NUMBER values .107
9.8.3 Representation of BOOLEAN values.108
9.8.4 Representation of LOGICAL values .109
9.8.5 Representation of STRING values .110
9.8.6 Representation of BINARY values .111
9.8.7 Representation of ENUMERATION items.111
9.8.8 Representation of EXPRESS entity instances as values of attributes .112
9.8.9 Representation of values of SELECT types .112
9.8.10 Representation of aggregate values.115
9.8.11 Representation of values of non-constructed defined data types .123
10 XML document creation.128
10.1 General XML document structure using binding representation.128
10.2 Representation of EXPRESS schemas.128
10.3 Representation of data .129
10.3.1 Late binding XML documents .129
10.3.2 EXPRESS-typed Early Binding XML documents.130
10.3.3 Object Serialization Early Binding XML documents .132
10.3.4 Mixed representation XML documents.132
10.4 Use of XML Namespaces.133
Annex A (normative) Information object registration.135
Annex B (normative) The XML markup declaration set for late bound data .136
Annex C (normative) Representing EXPRESS schemas .140
Annex D (normative) Base architecture document type definition.168
Annex E (normative) Universal Resource Names for bindings of EXPRESS schemas .169
Annex F (normative) Valid populations of EXPRESS entity instances.170
Annex G (informative) Computer interpretable listings .180
Annex H (informative) Technical Discussions .181
Annex I (informative) Examples.187
Annex J (informative) User Guide to XML Encodings in 10303-28.295
Annex K (informative) Mapping of Object Serialization Early Binding to Late Binding using XSLT301
Annex L (informative) Mapping of EXPRESS-Typed Early Binding to Late Binding using XSLT 313
Annex M (informative)  Mapping from the EXPRESS Typed Early Binding to the Object
Serialization Early Binding .323
vi © ISO 2003 — All rights reserved

Annex N (informative)  Mapping from the Late Binding to the Object Serialization Early Binding 334
Bibliography.351
Index.352

Figures
Figure 1 - Relationship between markup declaration sets.7

Tables
Table J.1 Data encoding size comparison .299
Table J.2 Binding approaches to design issues .300

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.
In other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
— an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
— an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee
casting a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 10303-28 was prepared by Technical Committee ISO/TC 184, Industrial automation systems and
integration, Subcommittee SC 4, Industrial data.
This International Standard is organized as a series of parts, each published separately. The parts of
ISO 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 ISO 10303-1. A complete list of parts of ISO 10303 is available from the
Internet:
.
This part of ISO 10303 is a member of the implementation methods series.
viii © ISO 2003 — All rights reserved

Introduction
ISO 10303 is an International Standard for the computer-interpretable representation of product
information and for the exchange of product data. The objective is to provide a neutral mechanism
capable of describing products throughout their life cycle. This mechanism is suitable not only for
neutral file exchange, but also as a basis for implementing and sharing product databases, and as a
basis for archiving.
This part of ISO 10303 specifies means by which schemas specified using the EXPRESS language
(ISO 10303-11) and data governed by EXPRESS schemas can be represented as an XML document
(Extensible Markup Language W3C Recommendation). Readers of this part of ISO 10303 should
have knowledge of the EXPRESS language, XML and XML-related standards in order to understand
its technical content.
For the representation of EXPRESS schemas, this part of ISO 10303 specifies an XML markup
declaration set based on the syntax of the EXPRESS language. EXPRESS text representation of
schemas is also supported.
For the representation of data corresponding to an EXPRESS schema, this part of ISO 10303 takes
two broad approaches. One approach is to specify a single markup declaration set that is independent
of the EXPRESS schema and can represent data for any schema. This approach is called late binding.
The second approach is to specify the results of the generation of a markup declaration set that is
dependent on the EXPRESS schema. This approach is called early binding.
This part of ISO 10303 specifies one late binding and two early bindings. Future editions of this part
of ISO 10303 are expected to include additional early bindings.
The markup declaration sets in this part of ISO 10303 are intended as formal specifications for the
appearance of markup in conforming XML documents. These declarations may appear as part of
Document Type Definitions (DTDs) for such documents. Future editions of this part of ISO 10303 are
expected to include specifications for the use of XML Schema [3] for this purpose.
EXAMPLE 1 For the following EXPRESS schema:
SCHEMA my_schema;
ENTITY an_entity;
attr1 : STRING;
END_ENTITY;
END_SCHEMA;
The corresponding XML markup would be:

my_schema

an_entity


attr1





The late binding is a single markup declaration set that can be used to represent data corresponding to
any EXPRESS schema. Additionally, the late binding can be used as the base architecture for early
bindings as specified by the Architectural Form Definition Requirements in ISO 10744:1997
(HyTime). One such early binding is specified in this part of ISO 10303. That early binding, called
the EXPRESS-typed Early Binding, preserves many of the data types defined in EXPRESS schemas.
EXAMPLE 2 For the following EXPRESS schema:
SCHEMA my_schema;
ENTITY an_entity;
attr1 : STRING;
END_ENTITY;
END_SCHEMA;
a set of late-bound data as XML markup might be:



an attr1 value



and the same data using the EXPRESS-typed Early Binding is:
schema_identifier="My_schema Edition 2">

an attr1 value


Early bindings can also be specified that are not architecturally compatible with the late binding. In
this part of ISO 10303, these bindings are related to the late binding through the specification of a
means of transforming data represented using that early binding into the same data represented using
the late binding. Transformations of this nature are specified that use XSLT (XSL Transformations
W3C Recommendation). XSLT is a language for transforming one XML document into another XML
document. One such early binding and XSLT transformation generation is specified in this part of
ISO 10303. That early binding, called the Object Serialization Early Binding, is based on object
serialization patterns for programming languages.
EXAMPLE 3 For the following EXPRESS schema:
SCHEMA my_schema;
ENTITY an_entity;
attr1 : STRING;
END_ENTITY;
END_SCHEMA;
x © ISO 2003 — All rights reserved

a set of Object Serialization Early Binding data as XML markup might be:


an attr1 value

Several components of this part of ISO 10303 are available in electronic form. This access is provided
through the specification of Universal Resource Locators (URLs) that identify the location of these
files on the Internet. If there is difficulty accessing these files contact the ISO Central Secretariat, or
contact the ISO TC 184/SC4 Secretariat directly at: sc4sec@cme.nist.gov.
TECHNICAL SPECIFICATION ISO/TS 10303-28:2003(E)
Industrial automation systems and integration —
Product data representation and exchange —
Part 28:
Implementation methods: XML representations of EXPRESS
schemas and data
1 Scope
This part of ISO 10303 specifies use of the Extensible Markup Language (XML) to represent schemas
specified using the EXPRESS data specification language, ISO 10303-11, and data that is governed
by EXPRESS schemas.
The following are within the scope of this part of ISO 10303:
 specification of XML markup declarations that enable EXPRESS schemas to be represented using
XML;
 specification of a single XML markup declaration set that is independent of the EXPRESS
schema and formally describes the XML representation of data governed by any schema;
NOTE 1 XML markup declarations specified using this method are referred to as late bound, in that they may
be used without change to represent data governed by any EXPRESS schema. This part of ISO 10303 allows for
a number of choices in representing the data.
 for an arbitrary EXPRESS schema, specification of an XML markup declaration set that
corresponds to the schema and formally describes the XML representation of data governed by that
schema;
NOTE 2  XML markup declarations specified using these methods are referred to as early bound, in that they
are specific to a given EXPRESS schema.
 specification of the mapping between XML markup declarations corresponding to a specific
schema and the XML markup declarations independent of any schema;
 specification of the form of XML documents containing EXPRESS schemas and data governed
by EXPRESS schemas;
 specification of the representation of EXPRESS primitive data type values as element content and
as XML attribute values.
The following are outside the scope of this part of ISO 10303:
 specification of XML markup declarations corresponding to an EXPRESS schema that depend on
the semantic intent of the EXPRESS schema;
 specification of mappings from XML markup declarations to an EXPRESS schema;
ISO 2003 - All rights reserved 1

NOTE 3 Given a set of XML markup declarations and one or more corresponding data sets, it is feasible to
create an EXPRESS schema that captures the semantic intent of the data. However, this requires an
understanding of the meaning and use of the data that may not be captured by the XML markup declarations.
 specification of the mapping to an EXPRESS schema from an XML representation of that
schema;
 specification of the mapping to an EXPRESS schema from XML markup declarations that have
been derived from that schema;
 any mapping to or use of XML schema [3].
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 6093:1985, Information processing — Representation of numerical values in character strings
for information interchange
ISO/IEC 6429:1992, Information technology — Control functions for coded character sets
ISO 8601:1988, Data elements and interchange formats — Information interchange — Representation
of dates and times
ISO/IEC 8824-1:1998, Information technology — Abstract Syntax Notation One (ASN.1): Specification
of basic notation
ISO 10303-1:1994, Industrial automation systems and integration — Product data representation and
exchange — Part 1: Overview and fundamental principles
ISO 10303-11:1994, Industrial automation systems and integration — Product data representation
and exchange — Part 11: Description methods: The EXPRESS language reference manual
ISO 10303-22:1998, Industrial automation systems and integration — Product data representation
and exchange — Part 22: Implementation methods: Standard data access interface
ISO 10303-23:2000, Industrial automation systems and integration — Product data representation
and exchange — Part 23: Implementation methods: C++ language binding to the standard data access
interface
ISO 10744:1997, Information technology — Hypermedia/Time-based Structuring Language (HyTime)
2 ISO 2003 - All rights reserved

Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies.
Internet Engineering Task Force RFC 2045 November 1996 [cited 2000-08-15]. Available from
World Wide Web:
Uniform Resource Identifiers (URI): Generic Syntax. Internet Engineering Task Force RFC 2396
August 1998 [cited 2000-08-07]. Available from World Wide Web:

URN Syntax. Internet Engineering Task Force RFC 2141 May 1997 [cited 2000-09-28]. Available
from World Wide Web:
Extensible Markup Language (XML) 1.0. World Wide Web Consortium Recommendation 10
February 1998 [cited 2000-04-26]. Available from World Wide Web:

Namespaces in XML. World Wide Web Consortium Recommendation 14 January 1999 [cited 2000-
04-26]. Available from World Wide Web:
XML Linking Language (XLink) Version 1.0. World Wide Web Consortium Candidate
Recommendation 3 July 2000 [cited 2000-08-08]. Available from World Wide Web:

XML Transformations (XSLT) Version 1.0. World Wide Web Consortium Recommendation 16
November 1999 [cited 2000-08-07]. Available from World Wide Web:


3 Terms, definitions, and abbreviations
3.1 Terms defined in ISO 10303-1
For the purposes of this document, the following terms defined in ISO 10303-1 apply:
 data;
 information.
3.2 Other terms and definitions
For the purposes of this document, the following terms and definitions apply. Terms defined in the
XML 1.0 Recommendation and ISO 10303-11 are repeated below for convenience.
NOTE Definitions copied verbatim from other standards are followed by a reference to the source standard in
brackets. Definitions that have been adapted from other standards are followed by an explanatory note.
ISO 2003 - All rights reserved 3

3.2.1
context schema [or governing schema]
For an express_data element, the EXPRESS schema that contains the model of the data contained
in that element.
3.2.2
element
A bounded component of the logical structure of an XML document that has a type and that may have
XML attributes and content.
NOTE Adapted from XML 1.0 Recommendation.
3.2.3
entity data type reference
An XML element that specifies the instance identifier of an element and serves as a reference to that
element from the point at which the entity data type reference element appears.
NOTE An entity data type reference is a "pointer" to another element instance. The entity data type reference
declaration does not correspond to any EXPRESS declaration, but rather is derived from an EXPRESS entity
data type declaration. The name of entity data type reference declaration is called the entity data type reference
identifier. See 8.1.2 for an explanation of this concept.
3.2.4
EXPRESS attribute
representation of a property of an EXPRESS entity data type.
NOTE  Adapted from ISO 10303-11.
3.2.5
EXPRESS entity instance
entity (data type) instance
A named unit of data which represents a unit of information within the class defined by an entity. It is
a member of the domain established by an entity data type. [ISO 10303-11]
3.2.6
markup declarations
XML element type, XML attribute-list, XML entity and XML notation declarations that provide a
grammar for a class of XML documents.
NOTE  Adapted from XML 1.0 Recommendation.
3.2.7
schema instance
an information set, grouped for some purpose, that is governed by a single EXPRESS schema.
3.2.8
XML attribute
name-value pair associated with an XML element.
4 ISO 2003 - All rights reserved

NOTE  Adapted from XML 1.0 Recommendation.
3.2.9
XML document
A (text) data object that conforms to the XML requirements for being well-formed.
NOTE  Adapted from XML 1.0 Recommendation.
3.3 Abbreviations
For the purpose of this part of ISO 10303, the following abbreviations apply.
DTD Document Type Definition
ETEB EXPRESS-Typed Early Binding
HyTime Hypermedia/Time-based structuring language
OSEB Object Serialization Early Binding
SGML Standard Generalized Markup Language
URI Uniform Resource Identifier
URN Uniform Resource Name
XLink XML Linking Language
XML Extensible Markup Language
XSL Extensible Stylesheet Language
XSLT XSL Transformations
3.4 Terminology
EXPRESS and XML use similar or identical words for different concepts. The qualification ‘XML’
and ‘EXPRESS’ are used to distinguish between the different contexts. These are used with the
following terms:
 attribute;
 entity.
ISO 2003 - All rights reserved 5

4 Fundamental concepts, assumptions, and limitations
The EXPRESS language is a data specification language used to specify data types and constraints on
data representing information to be exchanged or shared. Such a specification is given as an
EXPRESS schema. ISO 10303 provides multiple implementation methods that can be used for data
described by an EXPRESS schema.
The Extensible Markup Language (XML) is a subset of ISO 8879 Standard Generalized Markup
Language (SGML) that has been specified to enable generic SGML to be served, received, and
processed on the World Wide Web. It provides a syntax for constructing XML documents where the
content of the XML document may be structured information as well as, or instead of, free text.
This part of ISO 10303 specifies how XML can be used to represent both EXPRESS schemas and
data governed by EXPRESS schemas.
4.1 Early and late binding
Given an EXPRESS schema, this part of ISO 10303 describes two approaches for defining an XML
markup declaration set for the schema. These two approaches are called late binding (or late bound)
and early binding (or early bound).
A late-bound XML markup declaration set is one that can be used in the same manner for any
EXPRESS schema. It does not define any constructs that are specific to the schema.
An early-bound XML markup declaration set is based on the specific EXPRE
...