Database programming problem - time management application

We have a need to devlop something akin to schedule+ but as part of a client server database system. The requirements are thus: Hold information about commitments. Commitments are represented by a combination of a date and time. There is no restriction on dates. Time must be kept at a granularity of 15-minutes. Information must be kept in an RDBMS as opposed to an OODBMS. We must be able to efficiently determine if commitments conflict. We must be able to group commitments under a common header. We must be able to efficiently "split" an individual commitment. Currently we have a prototype implemented that stores commitments as a pair of "points" on a graph where the x-axis represents date and the y-axis represents time. Using this implementation, a commitment is represented as a polygon with 4-vertices. I have read up on polygon intersections etc. but nothing appears to really help. Any suggestions as to how this can be improved. One suggestion was to use the RDBMS as a block management system for implementing our own record/index structure that could be better optimized to the performance characteristics of the problem. Please e-mail me with any suggestions as I have posted this to soooo-many news groups, it would be impractical to check them all. Regards, Simon. -- The views and opinions expressed here are my own and do not necessarily reflect those of my employer.