The Heraclitus DBPL With Application to Active Databases and Data Integration

The database programming language Heraclitus[Alg,C] is an extension of the C programming language that supports the relational algebra and novel constructs related to the specification of these semantics. In particular, the language supports deltas as “first-class citizens” — these are values corresponding to database updates, which may or may not be applied. Unlike previous work on differential files and hypothetical relations, Heraclitus supports operators for combining deltas, and also alternative implementations that incorporate the impact of deltas into conventional database operators (e.g., join).

This chapter describes the design and preliminary implementation of Heraclitus[Alg,C]. Two strategies for providing access to deltas have been implemented, one hash-based and the other sort-based. Initial evaluation of system performance demonstrates the feasibility of the language.

A key issue in active database systems, i.e., database systems that incorporate automatic firing of rules, concerns understanding alternative semantics of rule application. This chapter shows how deltas can be used in representing the effect of rule firings, and for representing virtual database states, as they arise in the specification of these semantics. The chapter also describes how Heraclitus can be used to provide efficient support of materialized integrated views. More generally, the Heraclitus framework appears useful in connection with hypothetical database access, version control, specifying concurrency protocols, and the resolution of update conflicts.