looking for a complete documentation for Drupal's database schema - need to have some overview well dear buddies, 

i am pretty new to drupal. Just set up a drupal commons

now i 'd like to add some data to my drupal, and i dont really understand the database model/scheme. Can somebody point me to some documentation? For example i need to understand the role of node, vocabulary, and all the tables and what is tid,vid,nid fieds... Then i could add data the sql way.

Of course I don't think complete documentation for Drupal's database schema exists. Well does any body have a  very very first attempt:

An ongoing attempt with comments for Drupal 6 can be seen here
http://drupal.org/node/79874

An analysis with SchemaSpy i found here
http://webdevgeeks.com/schemaspy/index.html

and overview i have seen here. 
http://upsitesweb.com/sites/upsites.co/files/drupal7_model_0.png

well who can give more hints - i love to hear from you - 
Again: i want to have some overview on the options i have to extend the group 
(running on http://www.schulcenter.org - and see here http://schulcenter.org/?q=group/schulen ) 

How can i configure / extend the groups (/on the database-level)?
How can i configure / extend the groups (/on the database-level)?

i wanna creat the following fields - (derived from the following shedule https://scraperwiki.com/scrapers/austrian-schools/ ) see the names of the collumns


name
adresse 
schultyp 
homepage 
ergänzender schulname 
beschreibung
schwerpunkte


can this be done best in groups !? Can i this set in the groups. Or should i do that in the so called - organic-groups

Note: as you see the site schulcenter.org should give an overview on schools
with a certain amount of data from the profile: the adress, the website..


a little image (a thumbnail of the website - shown in a block,)
a little description (approx 200 characters) what the site /the school does - some special programmes or something like that...


How to achieve this !? Love to hear from you any and all help will greatly be appreciated

love to hear from you 
zero
Check Drupal's Schema API. Here is the link to it. Also the Book "Pro Drupal Development" has an excellent chapter on Working with Databases.You might find that one useful too.