An Execution Model for CPL +

Query languages and their optimizations have been a very important issue in the database community. Languages for updating databases, however, have not been studied to the same extent, although they are clearly important since databases must change over time. While update languages for the relational model are quite simple and provide little opportunity for optimizations, update languages for complex value databases turn out to be more challenging. CPL+ is a language for updating complex value databases, based on primitive values, records, variants, and collections. The syntax of CPL+ is concise in that only the parts of the database that change are speciied. Furthermore, powerful optimization rules are available. In this report, we show the correctness of the optimization rules. Furthermore, we describe an execution model for CPL+ together with the underlying abstract storage model for a complex value database. We develop a formal framework for describing the workspace of updates-i.e. the set of physical objects that are accessed or updated within an update. Based on this notion, we analyse optimizations and present a selection of proofs that show that the rewriting rules are indeed cost reducing.