In doing some reading, I have come across a piece of information which
states that SAP's R/3 system uses over 20,000 tables in its database. 
Is there a listing/documentation that a non-customer can access?  I am
curious to see how the database is structured.

Hello Nelson,

interesting question. I've been working on the development and data
modeling side of sap R/3 for years and, yes there is more than 22,000
tables in an SAP system.

As the previous commenter pointed out, even if you don't have access
to an sap system, you can still access the very extensiv online help
at help.sap.com.

To give you a brief overview: The data dictionary in sap is set on top
of the database the customer uses. The tables are organized as a
typical relational database. All data is in tables, every table has
one or more key fields and might be linked to other tables by the
content of fields.

There is transaction data tables (i.e. purchase orders), master data
tables (i.e. vendors), administration or customizing data (over 7000
tables - i.e. vendor groups) and system related data tables (i.e. data
dictionary meta data).

The tables are further subdivided to principles of normalization(i.e.
purchase order header table and -item table) and organisational
hierarchy (i.e. general vendor data in one table, subsidiary specific
vendor data in another).

Besides tables the data dictionary offers structures, views (=joins),
indexing, data elements (=field templates), etc. and is the foundation
for all R/3 applications or 'modules'.

It's a very complex set of tables, but the complexity allows to pretty
much model every business' need on an R/3 system without much
development work.

In terms of some examples, if you can't access the 'business
navigator' on an sap system, here is a few web sites I found :

on Data Modeling:
http://www2.hs-harz.de/~hscheruhn/english/courses/Lectures/Lecture4-part1.ppt
http://ist.psu.edu/yen/421/Slides/SAP_ERDLab.ppt

Definitions from SAP:
http://www.sappoint.com/faq/faqdatam.pdf
http://help.sap.com/saphelp_45b/helpdata/en/e3/8d8b0b4b8811d18a100000e816ae6e/content.htm

Search Strategy:
sap "entity relationship model"

Hope this answers your question (I could go on for hours ;-).

Morgenlandfahrer

Thank you.  I wanted more, but this is a great answer for $5.00.  I
guess I shouldn't be so cheap.  :-)

Hi,
 Yes SAP has more than 20000 tables. You can refer http://help.sap.com
 which has the online help documents for the entire SAP products. To
know about database you have to search in Basis module or ABAP
programming section.

In general the database design is nothing different from any RDBMS.
One special thing is SAP's own programming language ABAP has special
syntax called "OPEN SQL" which is a set of backend database
independent SQL statements. The SAP system automatically convert them
to  suit the backend database like Oracle, SQL server, DB2 etc.

Hope it helps.
RAC

RAC, Thank you for responding.  As you are the only one to comments,
feel free to post this as an answer if you are a researcher.

Hi,
 I am Not a Google researcher. Want to become one. If you are
satisfied with the answer then, you can close the question.
Thanks,
RAC

Hi Nelson,

thanks for the tip and the good rating. Yes, there is a lot more to be
said about SAP database modeling, but you are right it gets very
expensive. SAP Consultants charge usually $50 to $500/h. A few days of
training runs you ca. $1500.

Cheers,
Morgenlandfahrer