Historically, there has been a need within the database community to extend the relational model to accommodate more real-world knowledge. It is interesting that many of the required extensions cannot be accommodated by the model theoretic paradigm for relational databases.

a. Perform a topical search on the large number of proposals that have been conducted in response to this need.

b. How can one begin to compare these proposals? Discuss the limitations you discover in your topical search. Why should one believe that the definitions for these proposals are correct or complete?

c. Claim: The kinds of real-world knowledge that these extended data models attempt to capture have natural representations as first order formulae. The benefits of this claim would be:

The nonlogical data models can be equivalently formalized by suitably restricted classes of first order theories. As a result, the semantics of the nonlogical data model would be precisely defined by its logical content; two different nonlogical data models could be compared; the definition of an answer to a query remains the same as long as the extension to the data model is first order definable; and integrity constraints remain the same as long as the extension to the data model is first order definable. Verify this claim.