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Created: November 16, 2002.
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ISO SC34 Publishes Draft Reference Model for Topic Maps (RM4TM).

A posting from Steven R. Newcomb announces the availability of a first public draft of The Reference Model for Topic Maps (RM4TM), produced by members of the ISO/IEC JTC 1/SC34 Topic Map Models Project. The Reference Model defines "an abstract graph structure for the representation of relationships between subjects, rules for defining Applications of the Topic Maps paradigm, and rules for processing the information contained in topic maps. The primary objective of the Topic Maps paradigm is to make everything known about every subject accessible from a single location." In Newcomb's summary, the draft document "shows how to regard any data content notation, database schema, etc., as a topic map notation, so that its knowledge content can be automatically and losslessly amalgamated with all other kinds of knowledge content into a comprehensive topic map that honors the Subject Location Uniqueness Objective. The Subject Location Uniqueness Objective is to have one single subject per node, and for every participating subject to have one single node, even after any number of diverse topic maps have been merged together." ISO SC34 is also creating two new topic map standards: ISO 18048 "Topic Maps Query Language (TMQL)" provides a kind of SQL (or XML Query) for topic maps; ISO 19756 "Topic Maps Constraint Language (TMCL)" provides a schema or constraint language for use in constraining what is allowable to say in the topic map.

"RM4TM provides guidelines for defining TM Applications in general, including the Standard Application, while the Standard Application (SAM), with its powerful ontological notions of topic names, topic occurrences, and user-defined associations among topics, is the centerpiece of most current work in the arena of Topic Maps." [2002-11-26 statement in the TM "Guide"]

From the posting of Steve Newcomb:

The draft RM4TM establishes something like an assembly language for a "topic maps machine" that has only eight instructions. The development of a Syntax Processing Model (as that term is defined by the RM4TM), such as a Syntax Processing Model for the XTM syntax, is similar to the design requirements for a compiler that outputs code suitable for a RISC machine that has only eight instructions -- the "Eight Forms of Connectedness" described in the draft RM4TM. Once the information takes the form of a topic map graph, it is automatically mergeable in such a way as to achieve the Subject Location Uniqueness Objective.

I hope that everyone responsible for the Semantic Web, .NET, public safety and emergency management, government transparency and secrecy, etc. etc., will sit up and take notice. I know of no other standard or recommendation, proposed or unproposed, to the general problem of civilization-wide information aggregation, that allows diverse knowledge to be aggregated losslessly, while honoring the Subject Location Uniqueness Objective.

Before dismissing this idea on the basis that "graphs don't scale", first see what the RM4TM really is (it's a set of definition requirements for Topic Maps Applications), and then consider whether and how a wide-area network of knowledge-serving peers can act as a machine that supports eight instructions.

Introduction from the 2002-11-16 RM4TM specification:

This Reference Model for ISO 13250 Topic Maps (RM4TM) provides a framework for the definitions of Topic Map Applications (TM Applications). Diverse topic maps that conform to diverse TM Applications that are defined in keeping with this framework can be interpreted and amalgamated automatically by independently implemented systems, without losing information, and with predictable results.

Many of the key advantages of the Topic Maps paradigm derive from the achievement of its primary objective, the "Subject Location Uniqueness Objective", which is to make everything known about every subject in a topic space accessible from a single location within that space. The achievement of the Subject Location Uniqueness Objective means that the efficiency with which users can find information is maximized, not only because the subject's single location, once found, acts as a comprehensive catalog of the things that are known about it, but also because the subject's location can be found in terms of any of its relationships to other subjects.

This RM4TM facilitates the development of TM Applications and systems that can achieve the Subject Location Uniqueness Objective with respect to all subjects, including those that are only implicit in interchangeable topic map instances, as well as with respect to subjects that are relationships (and aspects of relationships) among other subjects.

Moreover, this RM4TM facilitates the development of TM Applications and implementations that can amalgamate the topic spaces represented by topic maps that conform to diverse Topic Maps Applications into a single resulting topic space in which each subject has a single location, there is no redundant information, and all of the information represented by the comprising topic maps is preserved.

This RM4TM provides definition requirements for user-defined Topic Map Applications that allow such definitions to serve as contracts between topic map creators, users, and system implementers, such that when the interchange or amalgamation of topic maps fails due to nonconformance to the definition of a Topic Maps Application, the nonconforming aspects of the topic maps or system implementations can be identified.

SAM. About The Standard Application Model for Topic Maps: " The SAM document "defines the structure and interpretation of topic map information by defining the semantics of topic map constructs using prose, and the structure of such constructs using a formal data model. Together with the Reference Model specification and the HyTM syntax specification this document will supersede ISO/IEC 13250:2002 Topic Maps, ISO, Geneva, 2002. Together with the XTM syntax specification this document will supersede XML Topic Maps (XTM) 1.0 Specification, TopicMaps.Org, 2001. It is intended to become part of the new ISO 13250 standard."

Overview of Topic Maps from the "Guide to the Topic Map Standards":

The topic maps work started out within the International Organization for Standardization (ISO), in a part of it today known as SC 34 (SC is short for subcommittee). This subcommittee works with SGML, DSSSL, HyTime, font standards, topic maps, the new XML schema language framework called DSDL, and other things. SC34 is divided into three working groups (WGs), and the topic maps work is done by WG3.

To [...] adapt topic maps to the web, the TopicMaps.Org organization was set up to create a new topic map syntax based on XML and URIs. The syntax TopicMaps.Org created is known as XTM (XML Topic Maps), and solves the problems described above. Today, the HyTM syntax is rarely used, as most people use XTM, precisely for these three reasons. In October 2001 the XTM DTD was accepted into ISO 13250, and so the second edition of ISO 13250 now contains two syntaxes: HyTM and XTM... The current ISO 13250 defines two interchange syntaxes (XTM and HyTM), but does not explain how they relate to one another. There are a number of non-trivial differences between the syntaxes, which is what makes this a problem...

ISO SC34 has resolved to create two new topic map standards:

  • ISO 18048: Topic Maps Query Language (TMQL) is a query language for topic maps. This language is intended to be a kind of SQL (or XML Query) for topic maps, and will greatly simplify topic map application development by making it much easier to extract information from topic maps. A requirements specification has been created.
  • ISO 19756: Topic Maps Constraint Language (TMCL) [will provide] a schema or constraint language for topic maps. Using TMCL one can write schemas for topic maps that constrain what is allowed to say in the topic map, such as 'a person must be born in a place,' 'a person must have at least one name,' and so on. A requirements draft has been created.

While the community is generally satisfied with the two syntaxes, their specifications are in need of improvement on three counts: (1) Not all developers interpret them the same way; (2) They need to clearly relate the two syntaxes to one another; (3) They do not provide suitable foundations for the TMQL and TMCL standards. ISO SC34's solution to this is the topic map data model work that was started in May 2001, and is now beginning to produce tangible results. See N0298R1, N0299, and the SAM home page.

ISO SC34's current plan is to revise ISO 13250 into a multi-part standard that resolves the problems described in the previous section. A key part of this new edition of the standard will be what is known as the Standard Application Model (SAM), a formal data model for topic maps. This model will be based on the same formalism as the XML Information Set. It will define the allowed structure of topic maps, as well as how to perform key operations such as merging and duplicate removal. The SAM is what will allow SC34 to solve the problems with the interpretations of the specifications, relate HyTM and XTM to one another, and create a foundation for TMQL and TMCL.

The new ISO 13250 will include a model known as the Reference Model, which is a more abstract graph model of topic maps. In this model, names and occurrence resources turn into nodes on the same level as topics, and they are related to their topics using an association-like structure of nodes and arcs. The result is a model that uses fewer constructs than the SAM, and which can be extended without changing the metamodel. The Reference Model provides a mechanism for explaining the relationships between different knowledge representations, such as topic maps, RDF, and KIF. This will make it easier for topic maps to interoperate with these other knowledge representations. It is planned that the SAM part of the standard will include a normative mapping of the SAM to the Reference Model. The TMQL and TMCL standards will thus relate to the Reference Model through the SAM. Obviously, it is very important that the SAM and the RM are consistent, and much work will go into ensuring that this is the case.

The parts of the new ISO 13250 standard will be:

  • Part 0: A guide to the structure of the standard - (Currently unknown)
  • Part X: The Standard Application Model - (Lars Marius Garshol and Graham Moore)
  • Part X: The Reference Model - (Steven R. Newcomb and Michel Biezunski)
  • Part X: The XML Topic Maps syntax (XTM) - (Lars Marius Garshol and Graham Moore)
  • Part X: The HyTime Topic Maps syntax (HyTM) - (Lars Marius Garshol and Graham Moore)
  • Part X: Canonicalization of topic maps - (Currently unknown)

In order for topic maps created by different parties to merge correctly it is crucial that these parties use the same identifiers for their topics. This is unlikely to happen by itself, however, and therefore three Technical Committees (TCs) have been formed within OASIS, in order to work on something called published subjects. These are URIs and descriptions for concepts considered important by some publisher. The three OASIS TCs are: (1) Published subjects TC; (2) XML Vocabulary TC; (3) Geography and languages TC.

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