On Implementing a Language for Specifying Active Database Execution Models
Shahram Ghandeharizadeh, Richard B. Hull, Dean Jacobs, Jaime F. Castillo, Martha L. Escobar-Molano, Shih-Hui Lu, Junhui Luo, Chiu Tsang, Gang Zhou · 1993
A key issue when incorporating rules into database systems concerns understanding alternative semantics of rule application. The database programming language Heraclitus[Alg,C] is an extension of C that supports the relational algebra and novel constructs related to the specification of these semantics. In particular, the language supports deltas as "firstclass citizens" -- these are values corresponding to database updates, which may or may not be applied. Deltas are useful in representing the effect of rule firings, and for representing virtual database states, as they arise in the specification of several active database systems. 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). The framework also appears useful in connection with hypothetical database access, version control, specifying...