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This paper describes the design and implementation of the Ariel DBMS and it's tightlycoupled forward-chaining rule system. The query language of Ariel is a subset of POSTQUEL, extended with a new production-rule sublanguage. Ariel supports traditional relational database query and update operations efficiently, using a System Rlike query processing strategy. In addition, the Ariel rule system is tightly coupled with query and update processing. Ariel rules can have conditions based on a mix of patterns, events, and transitions. For testing rule conditions, Ariel makes use of a discrimination network composed of a special data structure for testing single-relation selection conditions efficiently, and a modified version of the TREAT algorithm, called A-TREAT, for testing join conditions. The key modification to TREAT (which could also be used in the Rete algorithm) is the use of virtual ff-memory nodes which save storage since they contain only the predicate associated with the memory n...

The World Wide Web (the Web) has made an enormous amount of data freely accessible over the Internet. However, finding the right information in the midst of this mountain of data has been likened to finding the proverbial needle in a haystack. Commonly used search engines (e.g., AltaVista) and directory services (e.g., Yahoo) have practical but limited success. The exponential growth of the Web is increasing the haystack rapidly. Instead of pull-based browsing, update monitoring is a promising area of research where the system brings the right information to the right user at the right time. In this paper we present the design and implementation of the Conquer continual query system, designed for update monitoring over the Web information sources. A Continual Query (CQ) is a standing query that monitors update of interest using distributed triggers and notifies the user of changes whenever an update of interest reaches specified thresholds or some time limit is reached. In co...

A new, efficient selection predicate indexing scheme for active database systems is introduced. The selection predicate index proposed uses an interval index on an attribute of a relation or object collection when one or more rule condition clauses are defined on that attribute. The selection predicate index uses a new type of interval index called the interval skip list (IS-list). The IS-list is designed to allow efficient retrieval of all intervals that overlap a point, while allowing dynamic insertion and deletion of intervals. IS-list algorithms are described in detail. The IS-list allows efficient on-line searches, insertions, and deletions, yet is much simpler to implement than other comparable interval index data structures such as the priority search tree and balanced interval binary search tree (IBS-tree). IS-lists require only one third as much code to implement as balanced IBS-trees. The combination of simplicity, performance, and dynamic updateability of the IS-li...

Rules provide the functionality for constraint enforcement and view maintenance. A provably correct implementation of both issues based on rules, requires confluent and terminating behaviour of the rule set. However, little work has been done so far on the static detection of these properties. In this paper, a design theory for rule sets in an OODBMS is developed. This paper introduces two predicates, viz., Terminate(n) and Independent, which imply respectively termination and confluency. Both predicates are characterised under two kinds of rule execution semantics: set and instance based. The decidability of the predicates is proven and it is shown that set and instance based semantics coincide whenever the rule set is independent and terminates. Moreover, sufficient conditions of low algorithmic complexity for both Terminate(n) and Independent under both kinds of semantics are given. 1991 CR Categories: H.2.1[Information Systems]: Logical Design- data models; H.2.3[Informat...

This paper describes a model that integrates the execution of triggers with the evaluation of declarative constraints in SQL database systems. This model achieves full compatibility with the 1992 international standard for SQL (SQL92). It preserves the set semantics for declarative constraint evaluation while allowing the execution of powerful procedural triggers. It was implemented in DB2 for common servers and was recently accepted as the model for the emerging SQL standard (SQL3). 1 Introduction Active databases are taking a prominent role in commercial database applications [6, 30, 29, 13]. With client/server solutions, applications are being developed by small, autonomous groups of developers with narrow views of the overall enterprise; the enterprise information system is very vulnerable to integrity violations because it lacks strict enforcement of the enterprise business rules. Active data proactively monitors events and, without user intervention, protects its own integrity...

Active real-time databases have emerged as a research area in which concepts of active databases and real-time databases are combined into a real-time database with reactive behavior. However, this marriage is not free from complications. The main problem is that timeliness, i.e., predictability and efficiency, is of paramount importance in real-time databases, while reactive behavior may add to the unpredictability of the database. This survey addresses reactive behavior and timing constraints from a database perspective. Results of both real-time databases and active databases are discussed, as well as projects which have done research on active real-time databases. Keywords. Active databases, reactive mechanisms, real-time systems, real-time databases, predictability, timeliness This work was supported by NUTEK (The Swedish National Board for Industrial and Technical Development). Contents 1 Introduction 1 2 Traditional databases 2 2.1 Database models and query languages : : ...

Active databases and real-time databases have gained increased interest in recent. Both active and real-time databases are considered as important technologies for supporting non-traditional applications such as computer integrated manufacturing (CIM), process control and air-traffic control. These applications are often event driven and need to react to events in a timely and efficient manner. In this paper we address the problem of merging active databases and real-time databases. Active real-time database is a fairly new area, in which very little research has been carried out so far. However, the use of active real-time database applications has a great potential. In this paper we address several issues and open questions such as semantics, assignment of time constraints and rule selection, which need to be considered when designing active real-time databases. We will highlight issues associated with event detection, rule triggering, rule selection and evaluation in a active realti...

This paper presents WebCQ, a continual query system for large-scale Web information monitoring.

This article presents an approach to build generic rule execution models for active databases. It introduces a framework that provides both informal and formal supports to design and develop rule execution engines well adapted to different uses of rules and to predict and understand the resulting behaviour of active applications. The framework may be seen as an implementable specification (a standard). The core of our approach is a parametric execution model and its functional semantics that can be used as a specification for the implementation of flexible and portable execution engines whatever the data models and the event models of the underlying DBMS are. The model called FL'ARE is based on dimensions characterizing the execution of rules and rule modules. Dimensions have been organized as constants and parameters into three layers. Such an approach allows the integration of heterogeneous rule modules within the same application, each of them having its own semantics bas...