Temporal conversion functions for multitemporal relational databases
Most research in the field of algebras for temporal relational databases concerns the study of operations within each of the formats transaction-time, valid-time, bitemporal and snapshot. Nevertheless, data of different temporal format (multitemporal relational data) should be allowed to interact. Two possible scenarios for this problem are: (1) federated databases, where the interaction is required of databases of different temporal format; (2) databases supporting selective versioning, where, due to the different update frequencies, the attributes are maintained in tables of different temporal formats. A solution to this interoperability problem is neither straightforward nor univocal, since the semantics differences among such data are quite deep. As suggested in [DGS94] for the multitemporal natural join, a first step for the definition of a multitemporal relational algebra can be the conversion to a common temporal format for the execution of operations. The semantic criteria at the basis of the temporal conversion functions in [DGS94] have been long debated for their safeness in the deduction or reconstruction of temporal information. In this paper we revise such criteria, discuss their problems and present several alternative solutions.
KeywordsMultitemporal Relational Data Temporal Conversion Functions
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