How to design a database for User Defined Fields?

Question

My requirements are:

• Need to be able to dynamically add User-Defined fields of any data type
• Need to be able to query UDFs quickly
• Need to be

Answer 1

I've managed this very successfully in the past using none of these options (option 6? :) ).

I create a model for the users to play with (store as xml and expose via a custom modelling tool) and from the model generated tables and views to join the base tables with the user-defined data tables. So each type would have a base table with core data and a user table with user defined fields.

Take a document as an example: typical fields would be name, type, date, author, etc. This would go in the core table. Then users would define their own special document types with their own fields, such as contract_end_date, renewal_clause, blah blah blah. For that user defined document there would be the core document table, the xcontract table, joined on a common primary key (so the xcontracts primary key is also foreign on the primary key of the core table). Then I would generate a view to wrap these two tables. Performance when querying was fast. additional business rules can also be embedded into the views. This worked really well for me.