Abstract. We show that production rules and persis-tent queues together provide a convenient mechanism for maintaining consistency in semantically heterogeneous multi-database environments. We describe a specification language and methods for automatically deriving production rules that maintain (1) existence dependencies, in which the presence of data in one database implies the presence of related data in another, and (2) value dependencies, in which the value of data in one database is baaed on the value of related data in another. The production rules derived from dependency specifications use persistent queues to monitor and maintain the dependencies automatically, asynchronously, incremen-tally, and correctly. 1

Integrating a production rules facility into a database system provides a uniform mechanism for a number of advanced database features including integrity constraint enforcement, derived data maintenance, triggers, alerters, protection, version control, and others. In addition, a database system with rule processing capabilities provides a useful platform for large and efficient knowledge-base and expert systems. Database systems with production rules are referred to as active database systems, and the field of active database systems has indeed been active. This chapter summarizes current work in active database systems; topics covered include active database rule models and languages, rule execution semantics, and implementation issues. 1 Introduction Conventional database systems are passive: they only execute queries or transactions explicitly submitted by a user or an application program. For many applications, however, it is important to monitor situations of interest, and to ...

Event-based systems are developed and used to integrate components in loosely coupled systems. Research and product development focused so far on e#ciency issues but neglected methodological support to build such systems. In this article, the modular design and implementation of an event system is presented which supports scopes and event mappings, two new and powerful structuring methods that facilitate engineering and coordination of components in event-based systems. We give a

This paper describes the design and implementation of NAOS, an active rule component in the objectoriented database system O2. The contribution of this work is related to two main aspects. The first concerns the integration of the rule concept within the O2 model, providing a way to structure applications. Rules are part of a schema and do not belong to a class. Program execution and data manipulation, including method calls, can be driven on rules. The second aspect concerns the way NAOS interacts with O2 Engine, the kernel of the O2 system. To support a reactive capability the object manager semantics has been extended, thus providing an efficient event detection. Applications produce events and the subscribed event types react to these events. As a result, rules are triggered. The semantics of rule processing we provide is achieved through functions associated with event types during their subscription. The subscription mechanism is general enough to be used by any event driven...

Database researchers have recognized that integrating a production rules facility into a database system provides a uniform mechanism for a number of advanced database features including integrity constraint enforcement, derived data maintenance, triggers, protection, version control, and others. In addition, a database system with rule processing capabilities provides a useful platform for large and efficient knowledge-base and expert systems. Database systems with production rules are referred to as active database systems, and the field of active database systems has indeed been active. This paper summarizes current work in active database systems and suggests future research directions. Topics covered include database rule languages, rule processing semantics, and implementation issues. 1 Introduction Database systems provide persistent storage for massive amounts of data and powerful interfaces for querying and modifying this data. Even so, most database systems are passive, si...

This paper gives methods for statically analyzing sets of active database rules to determine if the rules are (1) guaranteed to terminate, (2) guaranteed to produce a unique final database state, and (3) guaranteed to produce a unique stream of observable actions. If the analysis determines that one of these properties is not guaranteed, it isolates the rules responsible for the problem and determines criteria that, if satisfied, guarantee the property. The analysis methods are presented in the context of the Starburst Rule System. 1 Introduction Rules in active database systems allow specification of data manipulation operations that are executed automatically whenever certain events occur or conditions are met [DHW94,DW92,HW93]. Active database rules provide a general and powerful mechanism for many database features, including integrity constraint enforcement, derived data maintenance, triggers, alerters, authorization checking, and versioning. In addition, active database sy...

Active OODBMSs must provide efficient support for event detection, composition, and rule execution. Previous experience, reported here, building active capabilities on top of existing closed OODBMSs has proven to be ineffective. We propose instead an active OODBMS architecture where event detection and rule support are tightly integrated with the rest of the core OODBMS functionality. After presenting an analysis of the requirements of active OODBMSs, we discuss event set, rule execution modes, and lifespan of events supported in our architecture. We also discuss the coupling of event composition relative to transaction boundaries. Since building an active OODBMS ex nihilo is extremely expensive, we are building the REACH active OODBMS by extending Texas Instrument 's Open OODB Toolkit. Open OODB is particularly well suited for our purposes because it is the first DBMS whose architecture closely resembles the active database paradigm. It provides low-level event detection and invokes a...

This paper describes our development of the Starburst Rule System, an active database rules facility integrated into the Starburst extensible relational database system at the IBM Almaden Research Center. The Starburst rule language is based on arbitrary database state transitions rather than tuple- or statement-level changes, yielding a clear and flexible execution semantics. The rule system has been implemented completely. Its rapid implementation was facilitated by the extensibility features of Starburst, and rule management and rule processing is integrated into all aspects of database processing. Index terms: active database systems, database production rules, extensible database systems, expert database systems 1 Introduction Active database systems allow users to create rules---rules specify data manipulation operations to be executed automatically whenever certain events occur or conditions are met. Active database rules provide a general and powerful mechanism for traditiona...

Expert database systems extend the functionality of conventional database systems by providing a facility for creating and automatically executing Condition-Action rules. While Condition-Action rules in database systems are very powerful, they also can be very difficult to program, due to the unstructured and unpredictable nature of rule processing. We provide methods for static analysis of Condition-Action rules; our methods determine whether a given rule set is guaranteed to terminate, and whether rule execution is confluent (has a guaranteed unique final state). Our methods are based on previous methods for analyzing rules in active database systems. We improve considerably on the previous methods by providing analysis criteria that are much less conservative: our methods often determine that a rule set will terminate or is confluent when previous methods could not. Our improved analysis is based on a "propagation" algorithm, which uses a formal approach based on an extended relatio...

A formal framework is introduced for studying the semantics and expressiveness of active databases. The power of various abstract trigger languages is characterized, and related to several major active database prototypes such as ARDL, HiPAC, Postgres, Starburst, and Sybase. This allows to formally compare the expressiveness of the prototypes. The results provide insight into the programming paradigm of active databases, the interplay of various features, and their impact on expressiveness and complexity.