While much work has addressed the problem of maintaining materialized views, the important question of optimizing queries in the presence of materialised views has not been resolved. In this paper, we analyze the optimization question and provide a comprehensive and efficient solution. Our solution has the desirable property that it is a simple generalization of the traditional query optimization algorithm.>

The goal of the Papyrus project [3] is to provide tools and services to enable the integration and parallelization of specialized data managers so that data-intensive applications can be constructed easily and efficiently. In our terminology, a data manager (DM) is a set of specialized methods that manage persistent data. A collection of functions defines the interface to a DM and provides the only means of accessing its persistent data.

This paper demonstrates that a simple rule system can be constructed that supports a more powerful view system than available in current commercial systems. Not only can views be specified by using rules but also special semantics for resolving ambiguous view updates are simply additional rules. Moreover, procedural data types as proposed in POSTGRES are also efficiently simulated by the same rules system. Lastly, caching of the action part of certain rules is a possible performance enhancement and can be applied to materialize views as well as to cache procedural data items. Hence, we conclude that a rule system is a fundamental concept in a next generation DBMS, and it subsumes both views and procedures as special cases.

The rule subsystem that is being implemented in the POSTGRES DBMS is explained. It is novel in several ways. First, it gives users the capability of defining rules as well as data. Moreover, depending on the scope of each rule defined, optimization is handled differently. This leads to good performance both when there are many rules each of small scope and when there are a few rules each of large scope. In addition, rules provide either a forward-chaining or a backward-chaining control flow, and the system chooses the control mechanism that optimizes performance whenever possible. Priority rules can be defined, allowing a user to specify rule systems that have conflicts. This use of exceptions seems necessary in many applications. Database services such as views, protection, integrity constraints, and referential integrity can be obtained simply by applying the rules system in the appropriate way. Consequently, no special-purpose code need be included in POSTGRES to handle these tasks.>