Time-based attributes in an ER-scheme.

Hi all, I'm a last year computer sciences student and I'm doing my thesis on the subject of 'temporal attributes in (O)RDBM's'. On field of research is the extension of the Entity-Relationship model. I want to add a new kind of attribute: an attribute which has a value that depends on the time or date. So the very same entity can have diferent values for an attribute depending on the time/date. Does anyone know whether some research has already been done on this topic? Where can I find more information? URL's/whitepaper/thesises.. Thanks in advance... Arvid Claassen ======================================================== == Claassen Arvid =========== Antwerp University ======= === Dorpsstraat 17 ========= 2nd Lic. Comp. Sciences === ===== B-2070 Burcht ======= arvid.claassen@uia.ac.be === ====== Belgium =========== 0032-3-252.91.79 ============ ========================================================