When you are joining to an existing project you don't have good knowledge of internal project structures. Existing documentation may be inaccurate or just missing. In this case you can rely only on clean source code structure and source code comments. Based on them you can generate API docs using Javadoc or Pydoc for instance. But what with persistent data model stored in database? SchemaSpy comes with help here!
SchemaSpy is small (~200kB) Java application that is able to render schema retrieved from JDBC connection into set of "hyperlinked" HTML pages with Java Script and (if GraphViz installed) diagrams. Below you see one page of example output of this tool:
Installation is very simple. I'll describe integration process with Eclipse. First: download jar with application. Then create new Run configuration in Eclipse:
Add downloaded jar to classpath:
Then fill execution program arguments. My preferred list is as follows:
-t orathin -db XE -u <db-user> -p <db-password> -o /opt/c2p/schema-docs -dp /opt/lib/ojdbc14.jar -host localhost -port 1521 -schema <db-schema> -noimplied
"orathin" option is database type and ojdbc14.jar contains JDBC driver for this connection type. "-noimplied" option will make documentation generation faster and saves some disk space for big projects.
The only missing feature for me is to disable rendering of attributes on diagrams (some association-rich tables gives very big images that could kill Firefox browser). It's an open source so I hope to fix this soon and of course release a path :-)