XML has been used to encode many different types of information and one of its strengths lies in the ability of any XML-aware software to process any XML file. However, for some applications it is important that additional information is provided to allow for other relationships between data to be estblished. Two technologes that povide additional models fo the pocessing of their XML/SGML encoded content are Resource Description Framework (RDF) and Topic Maps. Both of these models allow relationships between atomic entities to be asserted forming the basis of a processing model that, it is hoped, will lead to better machine pocessing of information in a networked environment.

Topic Maps (from ISO) and RDF (from W3C) are similar in that they both address the same problem of finding resources, and they both do so by annotating information resources (though in rather different ways). They are also similar in that they both define an abstract model and an SGML/XML based interchange syntax. Both models are very simple and elegant at one level, but thanks to recursion both are also extremely powerful: in Topic Maps, most things are topics (not just the topics themselves); in RDF the value of a resource's property may itself be a resource which in turn has properties.

These approaches are different: Topic Maps take a topic-centric view whereas RDF takes a resource-centric view. Topic Maps start from topics and model a semantic network layer above the information resources; they have the capability of modelling knowledge without any reference to the underlying resources. RDF starts from resources and annotates them directly.

Because RDF is fundamentally a "framework for metadata", i.e. for attaching property-value pairs to information resources, it can do the same job as facets in Topic Maps. However, there is much ongoing discussion about how Topic Maps and RDF should work together.