use cases

[pablo platt <pa...@gmail.com>]

Hi,

I've read allot about couchdb but still trying to understand what are its
use cases,
and if I can use couchdb alone for projects or do I have to combine it with
relational db.

Database for an instant messenger server.
Obviously couchdb will be good at logging chat rooms and maybe contact cards
with arbitrary data.
Will it be good for handling user credentials, roster(contact list) and
session management?

Database for a social network.
Again, couchdb is good for handling blog posts and messages between users.
Will it be good for handling connections between users (social graph),
permissions, settings...?

On thing that is very appealing to me is that a client can access the db
directly for both read and write operations without
putting load on the application server. I wonder how far couchdb's
authentication and permission implementation can go with that.
If I understand correctly, a user need to add his credentials to each
request which is not very secure.
Can I use some kind of SASL and session management (Cookie or session id)?
Are the couchdb permissions all or nothing? For example, can I limit the
size and number of documents a user can create?

Thanks