A topic map expresses someone's opinion about what the topics are, and which parts of an information set are relevant to which topics. There is no limit to the number of topic maps that can be created above the same information set. Topic Maps are specified by ISO 13250, January 2000. While XML tags are directly inserted inside the information source, a topic map is a hyperlinking layer built above electronic information sources. XML information sources are by their nature, static and cannot be dynamically updated when the topic network is required to change.
Topic maps work in a layer above the data source and can add flexibility to knowledge management.
Information sets do not have to change in any way as numerous topic maps are applied to them to create new knowledge bases. As it turns out, XML has spawned a whole new family of standards that work with XML in a Web environment such as XSL, XSLT, XPointer, XPath, and XLink. In addition, two schema languages, RDF and XSD are emerging as well. So the specification of how to use topic maps in the XML environment is more complex than simply interchanging a well-formed XML topic map document.