TM4J is an open-source package for creating topic map processing applications. The core of TM4J is a set of Java APIs for parsing, manipulating and saving topic maps. TM4J supports different storage models for the processed topic map, and includes an implementation which stores the topic in memory; an implementation which stores the topic map in a relational database; and another which stores the topic map in an object-oriented database. The API of TM4J is constructed in such a way as to make the type of storage used for the processed topic map is almost completely transparent to both the application and developer and the user of the application.