what is the data dictionary?

once again I stumble about two realy dumb (and related) questions: 1) what is the data dictionary (or how can I identify objects which belongs to it)?
2) is there any spyhole to view into the row cache (like v$bh for the buffer cache)?

According to the documentation, the data dictionary is http://download.oracle.com/docs/cd/E11882_01/server.112/e10713/glossary.htm#CNCPT2033
"A read-only collection of database tables and views containing
reference information about the database, its structures, and its users."

The row cache is defined with http://download.oracle.com/docs/cd/E11882_01/server.112/e10713/glossary.htm#CNCPT44459
"A memory area in the shared pool that holds data dictionary
information. The data dictionary cache is also known as the row cache because it holds data as rows instead of buffers, which hold entire data blocks."
Even v$rowcache seems not as featured as I'd like it to be.

This question is not based on any need, just pure curiosity.

  thank you for any hint,
  Martin

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