Universal Temporal Extensions for Database Languages

Temporal reasoning and temporal query languages present diicult 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 ro-bustness 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 func-tionality can be captured by simpler constructs which can be applied uniformly to Datalog, QBE and SQL. Then, we show that an eecient implementation can be achieved by mapping into a diierent storage representation , and discuss a prototype built along these lines using the LDL++ system with extended aggregates.