Ontopia: The Topic Map Company


  • Download the Ontopia topic map DTD (strict version).
  • Download the XTM 1.0 DTD.

Note regarding the Ontopia topic map DTD:

The interchange syntax for topic maps was originally defined (in "ISO/IEC 13250:2000 Topic maps") as an SGML architecture, i.e. a meta-DTD that could either be used directly (as a normal SGML DTD) or indirectly (via a derived client DTD).

Ontopia's tools are all written in Java and support XML rather than SGML. (XML is a lightweight version of SGML that has been optimised for use on the web.) For that reason, a different, XML-conformant DTD is required. Under the auspices of TopicMaps.Org, a standardized XML-based representation for topic maps has now been specified as XML Topic Maps (XTM) 1.0. In October 2001, that DTD officially became part of ISO 13250.

Ontopia's products, including the free Omnigator, support both the XTM DTD and the XML version of the original ISO syntax (now known as HyTM, because it is based on HyTime). If you wish to use the ISO syntax, you are recommended to use the strict version of the DTD since this will prevent you from certain semantic markup errors that might affect the processing of your topic map.

tmstrict.dtd is basically a simple subset of the original SGML meta-DTD. It includes all the fundamental element types (topicmap, topic, topname, basename, sortname, dispname, occurs, assoc, assocrl, facet, and fvalue), and all necessary attributes (types, type, scope, etc.). HyTime-specific features have been removed and the addressing mechanisms (which are left open in the ISO version of the DTD) are fixed as follows:

  • References to topics use ID based addressing; i.e. the declared values of types, type, and scope attributes (and href attributes on assocrl elements) is either IDREF or IDREFS as appropriate.
  • References to external resources (via the href attributes on occurs and fvalue elements) use URLs.

N.B. The latest version of the Ontopia DTD no longer includes the optional, non-standard extension of a 'topic' attribute on the 'topicmap' element. The purpose of this attribute was to allow reification of the topic map. Now that XTM has provided an explicit method for reifying topic map constructs, this is no longer necessary. The preferred method, using ISO syntax, is based on the XTM method and requires the following steps:

  1. Add an ID attribute to the element you wish to reify (topicmap, occurrence, association, or association role).
  2. Use this ID as the value of the [identity] attribute on the topic which reifies the element in question.

We reproduce here the statement given on this page in the period before the publication of XTM 1.0:

(Note: The XTM specification will probably include a standard reification mechanism for any topic map construct. Once this has been defined, Ontopia will remove its non-standard extension and use this instead.)

The following topic maps, all of which can be viewed with Ontopia's Topic Map Navigator demo, illustrate the use of the Ontopia DTD:

Public subjects

The following public subjects are defined by Ontopia:

Denotes an association type that exhibits the property of transitivity (e.g. "located-in")
Types a class of occurrences that are to be regarded as the default occurrence of a topic.
Types a class of occurrences that are to be regarded as metadata.
Indicates that the variant is the plural form of a base name.

Public Subject Identifiers can be constructed for all the above public subjects by prepending the string http://psi.ontopia.net/xtm/. For examples, see the Opera topic map.