Database design question - Isolated, unrelated tables

I have a question regarding best practices in database design. In a relational database, is it wise/necessary to sometimes create tables that are not related to other tables through a foreign Key relationship or does this always indicate some sort of underlying design flaw. Something that requires a re evaluation of the problem domain?

The reason I ask is because in our application, the user can perform x number of high level operations (creating/updating projects, creating/ answering surveys etc. etc.). Different users can perform different operations and each operation can manipulate one or more table. This part of the system is done and working. Now there is a requirement to have some sort of audit logging inside the database (separate from the text based log file that the application generates anyway). This "audit logging" table will contain high level events that occur inside the application (which may or may not relate to a particular operation). This table is in some sense related to every other table in the database, as well as data that is not in the database itself (exceptions, external events etc.). For example : it might have entries that specify that at time x user created project y, at time A user filled out survey B, at time C LDAP server was down, At time D an unauthorized login attempt occurred etc.

As I said, these seems to suggest a stand alone, floating table with a few fields that store entries regarding whats going on the system without any direct relationship to other tables in the database. But I just feel uneasy about creating such an isolated table. Another option is to store the "logging" information in another schema/database, but that doubles the maintainance work load. Not really looking forward to maintaining/designing two different schemas.

I had a look at the microsoft adventureworks database schema diagram and they seem to have 3 standalong tables - AWBuildVersion, ErrorLog and DatabaseLog (unless i am reading it wrong!)

Any advice, Information or resources are much appreciated. Received on Mon Jun 25 2007 - 09:08:45 CEST