Associations represent relationships between subjects, and like occurrences they can be typed. This allows any kind of relationship to be expressed. The relationships in traditional classification schemes have very little semantic content, whereas in topic maps one generally tries to make the typing of associations as specific as possible.
Associations are the final construct we need in order to be able to fully represent the set of statements given at the end of section 3.2, and the diagram below shows the result.
In this figure, types are indicated with different colours, while we’ve left out the alternative names. The types of the associations can be seen from the yellow labels on the lines.
Compared to traditional classification schemes this is very different. First of all, we no longer have a hierarchy but a network of subjects. Secondly, the relationships between the subjects are clearly defined instead of being generic. From the point of view of searching, this is very powerful, since it allows us to do queries like “show me all technologies used with topic maps”, or “show me every interchange format based on SGML”, and so on. There are also other uses, as we will see.