ISO/IEC JTC 1/SC34 N0269

ISO/IEC JTC 1/SC34

Information Technology --

Document Description and Processing Languages

Proposed Topic Maps Core Model Requirements

This document proposes a set of requirements to guide the development of a Core Model for Topic Maps. This document only proposes requirements for the so-called"Level 0" Model, or, as it is called in this document, the "Core" Model. The requirements for the "Level 1" Model are not addressed by this document. A proposed set of requirements for a Level 1 Model appears in N 0266; our comments about it appear in N????.

1. Goals

The following are proposed as the goals of the Core Model.

1. The Topic Maps paradigm offers the potential to achieve a usable degree of "knowledge fusion" among sets of assertions emanating from diverse non-cooperating sources, governed by diverse ontologies and taxonomies, interchanged via diverse notations, and internally represented in diverse data structures. The Core Model will provide a rigorous and reliable basis for the integration of knowledge-bearing assertions as "Topic Map Information". (In this document, the term "Topic Map Information" means "Scoped assertions of relationships in which specific 'subjects' (as in 'subjects of conversation') play specific roles.")
2. The Core Model will provide a common substrate model to which all conforming processing models for all syntaxes used to interchange Topic Map Information will provide an explicit mapping.
3. The Core Model will provide guidance to those who wish to exploit the maximum knowledge-integration potential of the Topic Maps paradigm, without the constraints inherent in any specific interchange syntax, or inherent in the implicit or explicit processing model associated with such a syntax, or inherent in the semantics implicitly or explicitly supported by such a syntax.
4. The Core Model will be suitable for the representation of Topic Maps at any scale. Requirements for the implementation of distributed systems capable of supporting extremely large topic maps will be derivable from the Core Model.
5. The Core Model will be suitable for use as the basis of systems that must support collaborative development of integrated topic maps, even in the absence of agreement between them regarding ontologies, taxonomies, applications, computer systems, interchange syntaxes, notations, or common purpose.

2. Requirements

The following are proposed as constraints on the Core Model.

1. The Core Model must clearly and irreducibly define the essential nature of Topic Map Information in such a way that, from the perspective of the Core Model, all other semantics are application-defined. In other words, it must enumerate and define the Core semantics that will always and necessarily be represented (either implicitly or explicitly) in all topic maps, regardless of the applications that govern them, and regardless of the syntaxes and other conventions that may govern their representations and specific additional semantics.
2. The Core Model must show how application-defined semantics participate in the topic maps that they govern. The essential purpose of the Topic Maps paradigm is to provide the ability to assert and navigate relationships between all semantics, without exception. Therefore, no semantics -- neither the Core semantics, nor any application-defined semantics of any kind whatsoever -- can be assumed by the Core Model to be exempt from the possibility of full participation in the topic maps that they govern. This includes (but is not limited to) all classes of topics and associations, all naming conventions and constraints, and all of the semantic infrastructures required to support them.
3. The Core Model must demonstrate, by one or more examples, how specific data formats used to represent information that implicitly or explicitly employs one or more of the Core semantics can be interpreted and manipulated as Topic Map Information. The Core Model must provide and exemplify the use of a rigorous Topic Map modeling formalism that can be used to define and constrain the output of systems designed to take instances of some desired data format as input, and output a corresponding topic map (either as interchangeable data or as application-internal data structures).
4. The Core Model must define redundancy and constrain conforming systems in such a way that redundancy is eliminated from their internal representations of topic maps before they assure their users that topic map parsing has been completed. The Core Model must fully account for the side effects of eliminating redundancy. For example, it must clarify what becomes of the scopes of redundant assertions.
5. The Core Model must be such that the addition of new assertions and subjects to a given topic map cannot cause existing information about how to navigate from one existing topic to another to become invalid. The core model of RDF, for example, does not meet this requirement, because assertions (normally represented as arcs) do not necessarily become nodes until they are "reified". Assertions cannot be made about arcs until they have been reified, and reifying them so significantly alters the surrounding landscape that navigational information based on the former configuration of the landscape becomes invalid.
6. No semantic, feature, or constraint explicitly (or implicitly intended to be) provided by the existing XTM 1.0 and ISO 13250 syntaxes shall be incapable of being represented and supported in full conformance with the Core Model.
7. The Core Model shall provide means whereby the data that represent Topic Map Information can be used as subject identity points for the topics and assertions that these data represent, so that these topics and assertions can have other assertions made about them, in any other topic map, by referring to their corresponding source data as subject identity points.
8. The Core Model shall not constrain implementations of conforming systems in such a way as to dictate their internal data structures.
9. The Core Model shall not constrain the semantics added by conforming applications, nor their interchange syntaxes, nor their query languages or other functional interfaces.
10. The Core Model shall not constrain the extent to which applications impose additional constraints on systems or interchangeable instances of topic maps, or on the semantics they represent.
11. The Core Model shall provide and demonstrate facilities for rigorously modelling applications of the Core Model. These facilities shall be suitable for use in the Level 1 Model. The Core Model must gracefully accommodate the fact that these facilities will not necessarily be used in any given application.
12. The Core Model shall show how any syntax used for representing Topic Map Information can be understood in such a way as to allow that Topic Map Information to participate fully in topic maps represented in any other syntaxes.
13. The Core Model shall show how every subject and relationship, including but not limited to subjects (such as ontologies and taxonomies) and relationships defined by all applications of the Topic Maps paradigm, can participate fully in topic maps, even when they govern those same topic maps. Toward this end, the Core Model shall explicitly provide published subjects for each of its own key concepts, in a form suitable for reference by and use within conforming topic maps.