Tersus Studio includes an embedded hsqldb 1.7.3 database.
By default, if a project is not configured otherwise, the hsqlpdb database will be used (in standalone mode), with files maintained in the project's database folder (viewable from the file system/eclipse's Navigator view).
You should be able to access the database files from any jdbc-based sql client - there's actually a basic one (called Database Manager) embedded in the hsqldb.jar file used to access the database.You could also use a regular text editor to edit the database file (.script file), which defines both schema, and data.
If you do want to access the database from another client, make sure the embedded application server is not running.
For best results, use the Firefox browser..