ISO/IEC 13250-2:2006

INTERNATIONAL ISO/IEC
STANDARD 13250-2
First edition
2006-08-15


Information technology — Topic Maps —
Part 2:
Data model
Technologies de l'information — Plans relatifs à des sujets —
Partie 2: Modèle de données





Reference number
ISO/IEC 13250-2:2006(E)
©
ISO/IEC 2006

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ISO/IEC 13250-2:2006(E)
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ISO/IEC 13250-2:2006(E)
Page
Contents
Foreword. iv

Introduction. v
1 Scope. 1
2 Normative references. 1
3 Terms and definitions. 1
4 The metamodel. 4
4.1 Introduction. 4
4.2 Locators. 5
4.3 The fundamental types. 5
4.4 Datatypes. 6
5 The data model. 6
5.1 General. 6
5.2 The topic map item. 7
5.3 Topic items. 8
5.3.1 Subjects and topics. 8
5.3.2 Identifying subjects. 8
5.3.3 Scope. 9
5.3.4 Reification. 9
5.3.5 Properties. 10
5.4 Topic name items. 10
5.5 Variant items. 12
5.6 Occurrence items. 12
5.7 Association items. 13
5.8 Association role items. 14
6 Merging. 15
6.1 General. 15
6.2 Merging topic items. 15
6.3 Merging topic name items. 15
6.4 Merging variant items. 15
6.5 Merging occurrence items. 16
6.6 Merging association items. 16
6.7 Merging association role items. 16
7 Core subject identifiers. 17
7.1 General. 17
7.2 The type-instance relationship. 17
7.3 The supertype-subtype relationship. 17
7.4 Sort names. 18
7.5 The default name type. 18
Annex A (informative) Subject identifiers for defined terms. 19
Bibliography. 21
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ISO/IEC 13250-2:2006(E)


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 13250-2 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 34, Document description and processing languages.
This first edition of ISO/IEC 13250-2 is part of a multi-part standard. The complete series will cancel and
replace ISO/IEC 13250:2003.
ISO/IEC 13250 consists of the following parts, under the general title Information technology — Topic Maps:
⎯ Part 2: Data model
⎯ Part 3: XML syntax
⎯ Part 4: Canonicalization
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ISO/IEC 13250-2:2006(E)

Introduction

Topic Maps is a technology for encoding knowledge and connecting this encoded knowledge to relevant information
resources. Topic maps are organized around topics, which represent subjects of discourse; associations, representing
relationships between the subjects; and occurrences, which connect the subjects to pertinent information resources.
Topic maps may be represented in many ways: using Topic Maps syntaxes in files, inside databases, as internal data
structures in running programs, and even mentally in the minds of humans. All these forms are different ways of
representing the same abstract structure. It is that structure which this part of ISO/IEC 13250 defines, in the form of a
data model.
NOTE The phrase "topic maps" is used in two ways in this part of ISO/IEC 13250: as a (capitalized) proper noun, "Topic Maps",
denoting the name of ISO/IEC 13250; and as the plural of a common noun "topic map". Both terms are defined in Clause 3.
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INTERNATIONAL STANDARD ISO/IEC 13250-2:2006(E)
Information technology — Topic Maps —
Part 2:
Data model

1 Scope
This part of ISO/IEC 13250 specifies a data model of Topic Maps. It defines the abstract structure of Topic Maps, using
the information set formalism, and to some extent their interpretation, using prose. The rules for merging in Topic
Maps are also defined, as are some fundamental subject identifiers.
The purpose of the data model is to define the interpretation of the Topic Maps interchange syntaxes, and to serve
as a foundation for the definition of supporting standards for canonicalization, querying, constraints, and so on. All of
these standards fall outside the scope of this part of ISO/IEC 13250.
NOTE 1 This clause defines the scope of this part of ISO/IEC 13250. It should not be confused with the concept of "scope"
defined in 5.3.3, which only applies in the context of Topic Maps.
NOTE 2 This part of ISO/IEC 13250 does not have a conformance section since it is only a data model, and as such it has no
boundary with the outside world in terms of which conformance can be specified.
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.
NOTE Each of the following documents has a unique identifier that is used to cite the document in the text. The unique identifier
consists of the part of the reference up to the first comma, and referenced thus: [Identifier].
Unicode, The Unicode Standard, Version 4.0, The Unicode Consortium, Reading, Massachusetts, USA, Addison-
Wesley, 2003, ISBN 0-321-18578-1
RFC 3986, Uniform Resource Identifiers (URI): Generic Syntax, Internet Standards Track Specification, January 2005,
available at
RFC 3987, Internationalized Resource Identifiers (IRIs), Internet Standards Track Specification, January 2005,
available at
XML Infoset, XML Information Set (Second Edition), World Wide Web Consortium, 4 February 2004, available at

ISO 10646, Information technology — Universal Multiple-Octet Coded Character Set (UCS)
XML, Extensible Markup Language (XML) 1.0 (Third Edition), W3C Recommendation, 4 February 2004, available at

XML Schema-2, XML Schema Part 2: Datatypes Second Edition, W3C Recommendation, 28 October 2004, available
at
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE These definitions are reproduced from the body of this document; for those unfamiliar with the terminology the
definitions are best read in context. They are repeated here for reference.
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3.1
association
representation of a relationship between one or more subjects
3.2
association role
representation of the involvement of a subject in a relationship represented by an association
3.3
association role type
subject describing the nature of the participation of an association role player in an association
3.4
association type
subject describing the nature of the relationship represented by associations of that type
3.5
information resource
representation of a resource as a sequence of bytes; it could thus potentially be retrieved over a network
3.6
item identifier
locator assigned to an information item in order to allow it to be referred to
3.7
locator
string conforming to some locator notation that references one or more information resources
3.8
merging
process applied to a topic map in order to eliminate redundant topic map constructs in that topic map
3.9
occurrence
representation of a relationship between a subject and an information resource
3.10
occurrence type
subject describing the nature of the relationship between the subjects and information resources linked by the
occurrences of that type
3.11
reification
making a topic represent the subject of another topic map construct in the same topic map
3.12
scope
context within which a statement is valid
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3.13
statement
claim or assertion about a subject (where the subject may be a topic map construct)
3.14
subject
anything whatsoever, regardless of whether it exists or has any other specific characteristics, about which anything
whatsoever may be asserted by any means whatsoever
3.15
subject identifier
locator that refers to a subject indicator
3.16
subject indicator
information resource that is referred to from a topic map in an attempt to unambiguously identify the subject
represented by a topic to a human being
3.17
subject locator
locator that refers to the information resource that is the subject of a topic
3.18
topic
symbol used within a topic map to represent one, and only one, subject, in order to allow statements to be made about
the subject
3.19
topic map
set of topics and associations
3.20
topic map construct
component of a topic map; that is, a topic map, a topic, a topic name, a variant name, an occurrence, an association,
or an association role.
3.21
Topic Maps
technology for encoding knowledge and connecting this encoded knowledge to relevant information resources
3.22
topic name
name for a topic, consisting of the base form, known as the base name, and variants of that base form, known as
variant names
3.23
topic name type
subject describing the nature of the topic names of that type
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3.24
topic type
subject that captures some commonality in a set of subjects
3.25
unconstrained scope
scope used to indicate that a statement is considered to have unlimited validity
3.26
variant name
alternative form of a topic name that may be more suitable in a certain context than the corresponding base name
4 The metamodel
4.1 Introduction
The metamodel used in this document is the same as that used by the XML Information Set [XML Infoset]. An instance
of this data model consists of a number of information items, each one of which is an abstract representation of a
topic map construct. Every information item is an instance of some information item type, which specifies a number
of named properties which the information item shall have. Throughout this part of ISO/IEC13250 the term "information
item" refers to the information item types defined in this model, while information items of particular types are referred
to as "topic items", "topic name items", and so on.
The names of properties are written in square brackets: [property name], following the convention used in [XML
Infoset]. Every property has a type that constrains what values it may have. Properties are not allowed to have null
as their value unless this is explicitly stated in the definition of the property.
Certain properties in the model are specified as computed properties, which means that they are specified in terms
of how their values may be produced from other properties in the model. These properties are specified for reasons
of convenience or to better reflect the semantics of the data model but are strictly speaking redundant.
A number of constraints on the allowed instances of the model are also defined. The purpose of these constraints is
to prevent inconsistencies in instances of the data model.
All information item types and fundamental types defined in this part of ISO/IEC13250 have a well-defined test of
equality. This equality test is used to avoid duplicate values in properties whose values are of type set. Information
items have identity, independent of their values, so items can be compared both by identity and by value. Equality
throughout this part of ISO/IEC13250 should be taken to mean equality according to the rules defined for the types
of the values being compared.
UML diagrams [UML] are used in addition to the infoset formalism for purposes of illustration. These diagrams are
purely informative, and in cases of discrepancy between the diagrams and normative prose, the prose is definitive.
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Figure 1 — The class hierarchy
NOTE TopicMapConstruct is the abstract superclass of all classes used in these UML diagrams. It is used here to simplify
the UML diagrams using inheritance. The Reifiable class is also abstract, and is used as the common superclass of all classes
corresponding to item types which can occur in the [reified] property of topic items.
4.2 Locators
An information resource is a a representation of a resource as a sequence of bytes; it could thus potentially be retrieved
over a network. Topic maps can refer to information resources external to themselves in order to make statements
about them. These information resources are not part of the topic map; they are only referenced from it.
A locator is a string conforming to some locator notation that references one or more information resources. Locators
are always expressed in some locator notation, which is a definition of the formal syntax and interpretation of a class
of locators. The definition of locator notations is outside the scope of this part of ISO/IEC13250. All locators in this
model use the notation defined by [RFC 3986] and [RFC 3987].
4.3 The fundamental types
The values of information item properties may be either other information items, or values of one of the types defined
below:
String
Strings are sequences of Unicode scalar values (see [Unicode] and [ISO 10646]).
Strings are equal if they consist of the exact same sequence of Unicode scalar values.
NOTE 1 This part of ISO/IEC13250 does not require Unicode normalization to be applied to strings order to detect that
syntactically different but logically equivalent strings are in fact equivalent. The application of such logic is encouraged,
however. As it cannot be guaranteed that normalization will be performed reliance on normalization is strongly discouraged.
Set
Sets are collections of zero or more unordered elements that contain no elements that are equal to each other.
In this data model the elements of a set are always information items or strings.
Two sets are equal unless there exists an element in one set for which no equal element can be found in the
other.
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Null
Null is a type of exactly one value, used to indicate that a property has no value; it does not necessarily indicate
that the value of the property is unknown. Specifically, null has the same semantics as No Value in [XML
Infoset]. In this model null can never be contained in a set.
Null is distinct from all other values (including the empty set and the empty string); it is only equal to itself.
Locator
Locators are strings conforming to some locator notation.
Locators are equal if they consist of the exact same sequence of Unicode scalar values.
NOTE 2 This part of ISO/IEC13250 does not require normalization to be applied to the syntactical expressions of locators
in order to detect that syntactically different but logically equivalent locators are in fact equivalent. The application of such
logic is encouraged, however. As it cannot be guaranteed that normalization will be performed reliance on normalization is
strongly discouraged.
4.4 Datatypes
The only atomic fundamental types defined in this part of ISO/IEC13250 (in 4.3) are strings and null. Through the
concept of datatypes, data of any type can be represented in this model. All datatypes used shall have a string
representation of their value space and this string representation is what is stored in the topic map. The information
about which datatype the value belongs to is stored separately, in the form of a locator identifying the datatype.
For each datatype there is an IRI which identifies the datatype. This IRI is to be considered a subject identifier for the
datatype, so that a topic having this IRI as its subject identifier represents the datatype. Any such topics, if present,
do not affect the processing of the topic map.
This part of ISO/IEC13250 defines only the following three datatypes, but other datatypes may also be used. These
datatypes are all defined by [XML Schema-2]; the syntax of the XML datatype is defined by [XML].
String
This is the string datatype, as defined in 4.3. The identifier of this datatype is http://www.w3.org/2001/
XMLSchema#string.
IRI
This is the datatype of locators using the IRI notation; the IRIs shall be absolute. The identifier of this datatype
is http://www.w3.org/2001/XMLSchema#anyURI.
XML
This is the XML datatype, which represents XML document fragments. The identifier of this datatype is http://
www.w3.org/2001/XMLSchema#anyType.
NOTE The datatype of a string value may affect its interpretation. For example, the string value "AT&T" means precisely
what it says if the datatype is string, but means "AT&T" if the datatype is XML.
5 The data model
5.1 General
This clause defines the data model through the definition of a number of information item types together with their
meaning.
A topic map construct is a component of a topic map; that is, a topic map, a topic, a topic name, a variant name, an
occurrence, an association, or an association role.
An item identifier is a locator assigned to an information item in order to allow it to be referred to. This part of
ISO/IEC13250 does not constrain how item identifiers are assigned to information items.
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NOTE 1 In a sense item identifiers are identifiers for topic map constructs, but unlike subject locators and identifiers devoid of
any specified semantics. Item identifiers may be freely assigned to topic map constructs.
One specific use of item identifiers is in the deserialization from the XML syntax [ISO 13250-3] where item identifiers are created
that point back to the syntactical constructs that gave rise to the information items in the data model instance. In this case the item
identifier will point to the minimal syntactical construct of origin, which means that for topic items created from the XML syntax, for
example, the item identifier will point to the originating topic element, rather than the containing topicMap element.
Constraint: Duplicate item identifiers
It is an error for two different information items to have strings that are equal in their [item identifiers] properties.
NOTE 2 If two topic items have the same value in their [item identifiers] properties this is not an error, as the conflict will be
resolved by merging the topic items following the procedure in 6.2.
5.2 The topic map item
A topic map is a set of topics and associations. Its purpose is to convey information about subjects through statements
about topics representing those subjects. The topic map itself has no meaning or significance beyond its use as a
container for the information about those subjects.
NOTE Although the topic map does not represent anything, it may be reified in order to make statements about the topic map
(that is, the collection of topics and associations) as a whole. These statements may for example provide traditional metadata such
as author, version, copyright, or they may reference system metadata such as a schema for the topic map, external documentation
of it, and so on.
Figure 2 — The topic map item
The topic map item represents the topic map. Topic map items have the following properties:
1 [topics]: A set of topic items. All the topics in the topic map.
2 [associations]: A set of association items. All the associations in the topic map.
3 [reifier]: A topic item, or null. If not null, the topic that reifies the topic map.
4 [item identifiers]: A set of locators. The item identifiers of the topic map.
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5.3 Topic items
5.3.1 Subjects and topics
A subject can be anything whatsoever, regardless of whether it exists or has any other specific characteristics, about
which anything whatsoever may be asserted by any means whatsoever. In particular, it is anything about which the
creator of a topic map chooses to discourse.
EXAMPLE Examples of subjects for which topics may be created are:
— The moon.
— The Soviet Union. This subject no longer exists as an organizational unit, but the idea still exists, and so is still a subject.
— The letters 'A', 'B', 'C', and 'D'. This could be regarded as a single subject, i.e., a set with four elements, or as four distinct
subjects.
— Plato's notion of the Good. This subject is different from, but related to, "good" in the abstract, and John Stuart Mill's notion
of "good".
A topic is a symbol used within a topic map to represent one, and only one, subject, in order to allow statements to
be made about the subject. A statement is a claim or assertion about a subject (where the subject may be a topic
map construct). Topic names, variant names, occurrences, and associations are statements, whereas assignments
of identifying locators to topics are not considered statements.
NOTE The process of merging ensures that whenever two topics are known to represent the same subject they are merged.
It may well be, however, that two topics represent the same subject without this being detectable by the rules of this part of
ISO/IEC13250. Merging beyond the minimal merging required by the rules of Clause 6 is freely allowed, although such merging is
not required or described by this part of ISO/IEC13250. Most commonly this will be done by inferring the subject of the topics
from statements made about them.
5.3.2 Identifying subjects
Formal identification of subjects with locators allows topic maps to be merged safely and precisely, and also allows
the definition of subjects with semantics that can be implemented in Topic Maps systems. Examples of such s
...