CSDL includes elements Documentation/Summary and Documentation/LongDescription that, according to MSDN, can be used to document entities. The contents of these elements conveniently appear in the properties window of the entity design surface, so it is easy to jot a few notes in these fields as you’re working with entities.
Since the EDMX file is XML, it would be easy to write an XSLT stylesheet to pull documentation from these elements. Is there a standard tool for doing this? Are there any other advantages to using the CSDL documentation fields? Is anyone using these fields, and if so, have you found them to be an effective way to document your entities?
The documentation data stored in the CSDL is emitted as XML doc comments in the generated code. As a result, it will appear in the intellisense tooltips in Visual Studio automagically:
If you want to use it for more formal documentation you can use SandCastle (optionally together with the excellent frontend SHFB), or some other Xml DocComment extraction tool to build windows help files or help websites containing the documentation.
If your database is documented using the documentation attributes in SQL Server, you can extract that documentation from the database and populate the SSDL and CSDL comments using this tool: http://huagati.com/edmxtools/