The Topic Maps engine is the heart of Ontopia, since it takes care of storing and providing access to the topic maps in the system. Essentially, the engine is a set of Java APIs, for

• Accessing and modifying any part of a topic map
• Importing topic maps from file (in XTM 1.0, 2.0, CTM, TM/XML, or LTM format)
• Exporting topic maps to file (to XTM 1.0, 2.0, TM/XML, or LTM format)
• Converting from RDF to Topic Maps (and vice versa)
• Executing queries using the tolog query language
• Performing full-text search

The engine can keep topic maps in memory or store them in a relational database. The API to the engine is the same in both cases, so that applications can switch backends without changing anything more than the configuration. The following databases are supported:

• Oracle 8 or newer
• Microsoft SQL Server 2005 or newer
• PostgreSQL 7.4 or newer
• MySQL 5.0 or newer
• h2 version 1.1 or newer