User-Defined Aggregates in Database Languages
DBPL '99 Revised Papers from the 7th International Workshop on Database Programming Languages: Research Issues in Structured and Semistructured Database Programming
A Temporal Query Language for OLAP: Implementation and a Case Study
DBPL '01 Revised Papers from the 8th International Workshop on Database Programming Languages
IEEE Transactions on Knowledge and Data Engineering
Extending temporal databases to deal with telic/atelic medical data
Artificial Intelligence in Medicine
SQLST: a spatio-temporal data model and query language
ER'00 Proceedings of the 19th international conference on Conceptual modeling
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Temporal reasoning and temporal query languages present difficult research problems of theoretical interest and practical importance. One problem is the chasm between point-based temporal reasoning and interval- based reasoning. Another problem is the lack of robustness and universality in many proposed solutions, whereby temporal extensions designed for one language cannot be easily applied to other query languages e.g., extensions proposed for SQL cannot be applied to QBE or Datalog. In this paper, we provide a simple solution to both problems by observing that all query languages support (i) single-value based reasoning and (ii) aggregate-based reasoning, and then showing that these two modalities can be naturally extended to support, respectively, point-based and interval-based temporal queries. We follow TSQL2 insofar as practical requirements are concerned, and show that its functionality can be captured by simpler constructs which can be applied uniformly to Datalog, QBE and SQL. Then, we show that an efficient implementation can be achieved by mapping into a different storage representation, and discuss a prototype built along these lines using the LDL++ system with extended aggregates.