XML Topic Maps (XTM) 1.0

TopicMaps.Org Specification

Latest version:
This version:
Members of the TopicMaps.Org Authoring Group;
see Acknowledgements
Steve Pepper  <>
Graham Moore  <>
$Id: index.html,v 1.16 2001/08/06 14:31:44 pepper Exp $


This specification provides a model and grammar for representing the structure of information resources used to define topics, and the associations (relationships) between topics. Names, resources, and relationships are said to be characteristics of abstract subjects, which are called topics. Topics have their characteristics within scopes: i.e. the limited contexts within which the names and resources are regarded as their name, resource, and relationship characteristics. One or more interrelated documents employing this grammar is called a “topic map.”

TopicMaps.Org is an independent consortium of parties developing the applicability of the topic map paradigm [ISO13250] to the World Wide Web by leveraging the XML family of specifications.

This specification describes version 1.0 of XML Topic Maps (XTM) 1.0 [XTM], an abstract model and XML grammar for interchanging Web-based topic maps, written by the members of the TopicMaps.Org Authoring Group. More information on XTM and TopicMaps.Org is available at

All versions of the XTM Specification are permanently licensed to the public, as provided by the Charter of TopicMaps.Org.

Status of This Document

(This section describes the status of this document at the time of its publication. Other documents may supersede this document. For the latest version, refer always to the URL given above.)

This document has been reviewed by the TopicMaps.Org Authoring Group and other interested parties and has been endorsed by the Authoring Group as a TopicMaps.Org Specification. It is a stable document and may be used as reference material or cited as a normative reference from another document.

The English version of this specification is the only normative version. However, translation of this document into other languages is actively encouraged by TopicMaps.Org.

An errata list for this Specification will be maintained at

Please report errors in this document to

top Contents

top 1. Introduction

top-of-section 1.1 Origins

XML Topic Maps (XTM) is a product of the TopicMaps.Org Authoring Group (AG), formed in 2000 by an independent consortium named TopicMaps.Org, originally chaired by Michel Biezunski and Steven R. Newcomb, and chaired at the date of delivery of this specification by Steve Pepper and Graham Moore. The Participating Members of the XTM Authoring Group are listed in Annex H: Acknowledgements.

The origins of the topic maps paradigm itself date back to 1993, when it was first expressed as a working document in the context of the Davenport Group. The paradigm was more fully developed thereafter in the context of the GCA Research Institute (now known as IDEAlliance), in an activity called Conventions for the Application of HyTime, during and after which the paradigm was independently developed, implemented, and promulgated. Early in 2000, after several years of continuous effort by an international group of individuals, the topic map paradigm was fully formalized for the first time as an ISO International Standard, ISO/IEC 13250:2000. Almost immediately thereafter, TopicMaps.Org was founded in order to develop the applicability of the paradigm to the World Wide Web, and to realize its enormous potential to improve the findability and manageability of information.

top-of-section 1.2 Goals

The design goals for XTM are:

  1. XTM shall be straightforwardly usable over the Internet.
  2. XTM shall support a wide variety of applications.
  3. XTM shall be compatible with XML, XLink, and ISO 13250.
  4. It shall be easy to write programs that process XTM documents.
  5. The number of optional features in XTM is to be kept to the absolute minimum, ideally zero.
  6. XTM documents should be human-legible and reasonably clear.
  7. The XTM design should be prepared quickly.
  8. The design of XTM shall be formal and concise.
  9. XTM documents shall be easy to create.
  10. Terseness in XTM markup is of minimal importance.

This specification, together with XML 1.0 for markup syntax [XML], XLink 1.0 for linking syntax [XLink], XML Base for base URI resolution [XML Base], and the IETF URI specification [RFC 2396] (as updated by [RFC 2732]), provides all the information necessary to understand XTM 1.0 and create conforming topic map documents.

This version of the XTM specification and its associated materials may be distributed freely, as long as all text and legal notices remain intact.

top-of-section 1.3 Terminology

The terminology used to describe XTM documents is defined in the body of this specification and its annexes. The terms defined in this section are used in building those definitions.

addressable information resource

An information resource whose identity is computable (that is, a computer system can retrieve the resource and make deterministic comparisons between it, and some other resource, to establish their identity or difference). An example of an addressable information resource is the online version of this document. In this specification, the term resource is used synonymously with addressable information resource unless otherwise stated.

addressable subject

An addressable information resource, considered as a subject in and of itself, and not considered in terms of what an author meant by it. The identity of an addressable subject is by definition directly computable. (Cf. non-addressable subject.)

  1. A relationship between topics asserted by an <association> element.
  2. An <association> element.

association type
  1. One of the classes of association.
  2. The class of association specified by an <association> element's <instanceOf> child element. An association may belong to only one class.
  3. A topic whose subject is a class of association.

base name
  1. A child element (<baseName>) of a <topic> element.
  2. A name characteristic of a topic that is provided by the content of a <baseNameString> element. Base names must be unique within a given scope (cf. topic naming constraint).

See also variant name.


See topic characteristic.

consistent topic map

A topic map in which there is one topic per subject and no further opportunities for merging or duplicate suppression, as defined in Annex F: XTM Processing Requirements.

  1. A child element (<member>) of an <association> element.
  2. A set of topics that play a particular role in an association.

  1. The process of merging two topic maps, either as a result of explicit <mergeMap> directives, or for any application-specific reasons.
  2. The process of merging two topics.

The rules governing all forms of merging are given in Annex F: XTM Processing Requirements.

non-addressable subject

A subject that exists outside the bounds of the computer system and whose identity is therefore not computable. Examples of non-addressable subjects include William Shakespeare, the play Hamlet and its 1604-05 edition, the character Hamlet, the concept of vengeance, the organization Shakespeare & Company, etc. The identity of a non-addressable subject may only be established indirectly, for example through the use of a subject indicator.

  1. A child element (<occurrence>) of a <topic> element.
  2. A topic occurrence (q.v.).

occurrence type
  1. One of the classes of topic occurrence.
  2. The class of topic occurrence specified by an <occurrence> element's <instanceOf> child element. An occurrence may belong to only one class.
  3. A topic whose subject is a class of topic occurrence.

  1. A child element (<parameters>) of a <variant> element.
  2. Information, in the form of a set of topics, that expresses the appropriate processing context for a variant name.

processed topic map

The collection of topics, associations, and scopes which have been processed by the XTM processing application as defined in Annex F: XTM Processing Requirements.

processing requirements

The requirements on processing performed by a conforming XTM processor as defined in Annex F: XTM Processing Requirements.


See published subject indicator.

published subject indicator

A subject indicator that is published and maintained at an advertised address for the purpose of facilitating topic map interchange and mergeability.


The act of creating a topic. When anything is reified it becomes the subject of the topic thus created; to reify something is therefore to create a topic of which that thing is the subject. Reification of a subject allows topic characteristics to be assigned to the topic that reifies it: In other words, it makes it possible to discourse about that subject within the terms of the topic map paradigm.


See addressable information resource.


The role that a topic plays as a member of an association; the nature of its involvement in that association.

  1. The extent of the validity of a topic characteristic assignment. The context in which a name or an occurrence is assigned to a given topic, and the context in which topics are related through associations.
  2. The set of topics specified via a <scope> element.

See also unconstrained scope.

This specification places no constraints on how applications interpret scope.

  1. Anything that can be spoken about or conceived of by a human being. In the most generic sense, a subject is anything whatsoever, regardless of whether it exists or has any other specific characteristics, about which anything whatsoever may be asserted by any means whatsoever.
  2. Anything on which the author of a topic map chooses to discourse.
  3. Anything that is reified by a topic in a topic map; the organizing principle of a topic. Humans are the ultimate authorities for determining the subjects of topics.

See also subject identity, subject indicator.

subject identity
  1. The <subjectIdentity> child of a <topic> element.
  2. That which makes two subjects identical, or distinguishes one subject from another. The determination of subject identity is aided, and may be automated, by the use of published subject indicators.
  3. A criterion for merging topics as defined in Annex F: XTM Processing Requirements.

subject indicator

A resource that is intended by the topic map author to provide a positive, unambiguous indication of the identity of a subject. There are three ways of indicating a subject in a topic map:

  1. Pointing via a <topicRef> element to a <topic> element that shares the same subject;
  2. Pointing via a <subjectIndicatorRef> element to a resource that indicates the subject;
  3. Pointing via a <resourceRef> element to a resource that is the subject.

The subject indicated by a subject indicator may be either non-addressable or addressable. (Note that in case 3, the subject is necessarily addressable, since it is a resource.)

  1. A resource that acts as a proxy for some subject; the topic map system's representation of that subject. The relationship between a topic and its subject is defined to be one of reification. Reification of a subject allows topic characteristics to be assigned to the topic that reifies it.
  2. A <topic> element.

topic characteristic

One of the following:

  1. a topic name,
  2. a topic occurrence, or
  3. a role played by a topic in an association

A topic's names, occurrences, and roles played in associations are collectively known as its characteristics.

See also topic name, topic occurrence, and role.

topic characteristic assignment

The act of asserting that a given topic has a particular characteristic. Such assertions are deemed to be valid