Graham Moore, Kal Ahmed: "Topic Map Relational Query Language [PDF] (TMRQL) has been designed in order to provide a sound foundation for querying topics maps. To this end it does not define an entire new language but instead presents a core set of abstract relational views. The relational model provides a firm foundation for the development of a topic map query language.
Development in this direction would lead to a more accessible and usable language by a greater number of developers than a new and bespoke language. Developers would be familiar with the concepts and their existing tools would work with the data structures returned. To them, the topic map data model would appear as just another schema or view. In order that the TMRQL language is not bound to a single implementation schema, nor even, bound to a relational database implementation we define a set of Relational Views that provide an abstract relational model of the topic map data model. This abstract data structure is independent of any particular implementation yet provides a foundation to use the full power of the SQL language and helps with portability of TMRQL queries."