Active database management systems have been introduced for applications needing an automatic reaction in response to certain events. Events can be simple in nature or complex. Complex events rely on simpler ones and are usually specified with the help of operators of an event algebra. There are quite a few papers dealing with extensions of existing event algebras. However, a systematic and comprehensive analysis of the semantics of complex events is still lacking. As a consequence most proposals suffer from different kinds of peculiarities. Independent aspects are not treated independently leading to shady mixtures of aspects in operators. Moreover, aspects are not always treated uniformly. Operators may have other semantics than expected. This paper addresses these problems by an extensive and in-depth analysis of the foundations of complex events. As a result of this analysis, a (formal) metamodel for event algebras will be introduced that subdivides the semantics of complex event...

In this paper we analyse the differences between rational and reactive agent architectures, and propose a uniform agent architecture that aims to capture both as special cases. For this purpose we employ a proof procedure, to control the agent's behaviour, which combines definitions with integrity constraints. The proof procedure is general, and has been shown elsewhere to unify abductive logic programming, constraint logic programming and semantic query optimisation. We also employ a resource-bounded formalisation of the proof procedure which allows the agent's reasoning to be interrupted and resumed, so that observations and actions can be performed. 1 Introduction The traditional notion of a rational agent in Artificial Intelligence focuses on the agent's thinking process and downplays or ignores its interaction with the environment. This notion has been challenged in recent years by the contrary notion of a reactive agent that focuses on the agent's timely interaction with the env...

An important feature of many advanced active database prototypes is support for rules triggered by complex patterns of events. Their composite event languages provide powerful primitives for event-based temporal reasoning. In fact, with one important exception, their expressive power matches and surpasses that of sophisticated languages offered by Time Series Management Systems (TSMS), which have been extensively used for temporal data analysis and knowledge discovery. This exception pertains to temporal aggregation, for which, current active database systems offer only minimal support, if any. In this paper, we introduce the language TREPL, which addresses this problem. The TREPL prototype, under development at UCLA, offers primitives for temporal aggregation that exceed the capabilities of state-of-the-art composite event languages, and are comparable to those of TSMS languages. TREPL also demonstrates a rigorous and general approach to the definition of composite event language sema...

In this paper we take a first step towards characterizing active databases. Declarative characterization of active databases allows additional flexibility in studying the effects of different priority criteria between fireable rules, different actions and event definitions, and also to make claims about effects of transaction and prove them without actually executing them. Our characterization is related but different from similar attempts by Zaniolo in terms of making a clear distinction between actual and hypothetical execution of actions and allowing nondeterminism. We use the `choice' construct [SZ90] to characterize the non-determinism that arises when several rules can fire at the same time and the preference between them is not specified. We show through examples how our language allows us to express features of different active database systems.

We present a hierarchically structured transaction-oriented concept for a rule-based active database system. In [LL94, LHL95], we have proposedStatelog as a uni ed framework for active and deductive rules. Following the need for better structuring capabilities, we introduce procedures as a means to group semantically related rules and to encapsulate their behavior. In addition to executing elementary updates, procedures can be called, thereby de ning (sub)transactions which may perform complex computations. A Statelog procedure is a set of ECAstyle Datalog rules together with an import/export interface. Systemimmanent frame and procedure rules ensure both propagation of facts and processing of results of committed subtransactions. Thus, Statelog programs specify a nested transaction model which allows a much more structured and natural modeling of complex transactions than previous approaches. Two equivalent semantics for a Statelog program P are given: (i) a logic programming style semantics by a compilation into a logic program, and (ii) a model-theoretic Kripke-style semantics. While (ii) serves as a conceptual model of active rule behavior and allows to reason about properties of the speci ed transactions, (i) -- together with the appropriate execution model -- yields an operational semantics and can be used as an implementation of P.

Semantics represents a major problem area for active databases inasmuch as (i) there is no formal framework for defining an implementationindependent semantics of active rules, and (ii) the various systems developed so far have ad-hoc operational semantics that are widely different from each other. This situation contributes to the difficulty of predicting the run-time behavior of sets of rules: thus, ensuring the termination of a given set of rules is currently viewed as a major research issue. In this paper, we introduce a durable change semantics for active database rules; this semantics improves Starburst's deferred activation notion with concepts taken from Postgres and Heraclitus and the semantic foundations of deductive databases. We provide a formal logic-based model for this transaction-oriented semantics, show that it is amenable to efficient implementation, and prove that it solves the non-termination problem. 1 Introduction Several active database languages and systems hav...

Active databases must support rules triggered by complex patterns of composite temporal events. This paper proposes a general method for specifying the semantics of composite event specification languages. The method is based on a syntax-directed translation of the composite event expressions into Datalo!7s, whose formal semantics is then used to define the meaning of the original event expressions, We show that the method is applicable to languages such aq ODE, Snoop and SAMOS that are baed respectively on the formalisms of Finite State Machines, Even Graphs and Petri Nets. The proposed method overcomes various problems and limitations affecting such formalisms.

A major thrust of current research in active databases is allowing complex patterns of temporal events to serve as preconditions for rule triggering. Currently, there is no common formalism for specifying the semantics of composite events specification languages and different systems use an assortment of approaches including Finite State Machines, Petri Nets and Petri Nets. In this paper, we propose a unifying approach, which is based on a syntax-directed translation of the composite event expressions into Datalog 1S , whose formal semantics is then used to define the meaning of the original event expressions.

We present a state-oriented extension to Datalog called Statelog which comprises two kinds of rules within a simple, yet flexible unified framework, i.e. (i) passive query rules used to express queries and static integrity constraints, and (ii) active transition rules for defining state-changing operations. We show that Statelog is powerful enough to capture many typical active rule applications (including complex updates, integrity enforcement and incremental view maintenance strategies) while retaining a declarative, set-oriented, and deterministic semantics thus reconciling active and deductive databases. Using the Statelog framework, formal results on termination, expressiveness and complexity of active rules are established which carry over to related state-oriented languages like XY-stratified Datalog. We prove that it is undecidable for general Statelog programs whether a program terminates on all databases. We then develop syntactic criteria which guarantee program t...

The need to search for complex and recurring patterns in database sequences is shared by many applications. In this work, we discuss how to express and support efficiently sophisticated sequential pattern queries in relational database systems. Thus, we first