oracle ate

Does anyone have a writeup or deconstruction of the
implementation of Oracle's extensibility capabilities?

I am a long time ordbms proponent (illustra, informix and
now postgresql).  And I have heard mixed information
regarding Oracle's extensibility. Do they use a unified
type system?   Are cartriges separate processes? Do the
separate processes (if they are) share memory with the
server process or is all the communication through pipish
things. If I don't use their standard cartridges (image,
text, video) how easy is it to write my own.  Any GIS
specific pro or con info w/Oracle?  Am I asking the right
questions?

I would like to put the questions to rest and get on with it.

Feel free to point me to the right audience or source if
this is not a good question for this group.

thanks

elein@nextbus.com