, Exception, Clock, Externalg Granularity ae fMember, Subset, Setg Type ae fPrimitive, Composite g Operators ae for, and, seq, closure, times, not g Consumption mode ae fRecent, Chronicle, Cumulative, Continuous g Role 2 fMandatory, Optional, Noneg Condition Role 2 fMandatory, Optional, Noneg Context ae fDB T , BindE , DBE , DBC g Action Options ae fStructure Operation, Behavior Invocation, Update-Rules, Abort Inform, External, Do Instead g Context ae fDB T , BindE , BindC , DBE , DBC , DBA g ---behavior invocation, in which case the event is raised by the execution of some user-defined operation (e.g. the message display is sent to an object of type widget). It is common for event languages to allow events to be raised before or after an operation has been executed. ---transaction, in which case the event is raised by transaction commands (e.g. abort, commit, begin-transaction) ---abstract or user-defined, in which case a programming mechanism is used that allows an appli...

Many interesting application systems, ranging from workflow management and CSCW to air traffic control, are eventdriven and time-dependent and must interact with heterogeneous components in the real world. Event services are used to glue together distributed components. They assume a virtual global time base to trigger actions and to order events.

Triggers are the basic ingredient of active databases. Ode triggers are event-action pairs. An event can be a composite event (i.e., an event composed from other events). Composite events are detected by translating the event specifications into finite state machines. In this paper, we describe the integration and implementation of composite event based triggers into the Ode object database. We focus on implementation details such as the basic trigger events supported, the efficient posting of these events, the handling of transactionrelated events, and the integration of triggers into a real database. We also describe the run-time facilities used to support trigger processing and describe some experiences we gained while implementing triggers. We illustrate Ode trigger facilities with a credit card example. 1 Introduction Ode [1, 2] is a database system and environment based on the object paradigm. The database is defined, queried, and manipulated using the database programming lang...

Monitoring the behaviour of computing systems is an important task. In active database systems, a detected system behaviour leads to the triggering of an ECA (event-condition-action) rule. ECA rules are employed for supporting database management system functions as well as external applications. Although distributed database systems are becoming more commonplace, active database research has to date focussed on centralised systems. In distributed debugging systems, a detected system behaviour is compared with the expected system behaviour. Di erences illustrate erroneous behaviour. In both application areas, system behaviours are speci ed in terms of events: primitive events represent elementary occurrences and composite events represent complex occurrence patterns. At system runtime, speci ed primitive and composite events are monitored and event occurrences are detected. However, in active database systems events are monitored in terms of physical time and in distributed debugging systems events are monitored in terms of logical time. The notion of physical time is di cult in distributed systems because

Reactive Web systems, Web services, and Web-based publish/subscribe systems communicate events as XML messages, and in many cases require composite event detection: it is not sufficient to react to single event messages, but events have to be considered in relation to other events that are received over time. Emphasizing language design and formal semantics, we describe the rule-based query language XChange EQ for detecting composite events. XChange EQ is designed to completely cover and integrate the four complementary querying dimensions: event data, event composition, temporal relationships, and event accumulation. Semantics are provided as model and fixpoint theories; while this is an established approach for rule languages, it has not been applied for event queries before.

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The architecture and the implementation of the active, object-oriented database management system SAMOS 2 are described. SAMOS is a research prototype extending a commercial object-oriented database management system with reactive behavior specified in the form of event-condition-action rules. This paper describes the various components of SAMOS for event detection, rule management, rule execution, and transaction management, and explains how they work and interact upon rule definition and execution. The current architecture of SAMOS is evaluated, experiences with the layered approach are described, and drawbacks are identified.

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 : : ...

In the last years the deployment of embedded real-time systems has increased dramatically. At the same time, the amount of data that needs to be managed by embedded real-time systems is increasing, thus requiring an efficient and structured data management. Hence, database functionality is needed to provide support for storage and manipulation of data in embedded real-time systems. However, a database that can be used in an embedded real-time system must fulfill requirements both from an embedded system and from a realtime system, i.e., at the same time the database needs to be an embedded and a real-time database. The real-time database must handle transactions with temporal constraints, as well as maintain consistency as in a conventional database. The main objectives for an embedded database are low memory usage, i.e., small memory footprint, portability to different operating system platforms, efficient resource management, e.g., minimization of the CPU usage, ability to run for long periods of time without administration, and ability to be tailored for different applications. In addition, development costs must be kept as low as possible, with short time-to-market and a reliable software. In this report we survey embedded and real-time database platforms developed in industrial and research environments. This survey represents the state-of-the-art in the area of embedded databases for embedded real-time systems. The survey enables us to identify a gap between embedded systems, real-time systems and database systems, i.e., embedded databases suitable for real-time systems are sparse. Furthermore, it is observed that there is a need for a more generic embedded database that can be tailored, such that the application designer can get an optimized database for a specif...

Rule-based (re)active systems are a commonly accepted solution in the area of nonstandard applications in order to express an event-driven and constraint-driven system environment. Several attempts have been made to integrate active concepts into object-oriented databases and to extend active knowledge models to gain more and more expressive power and flexibility. Unfortunately, execution models of active systems do not fully exploit all the advantages of the provided knowledge models. Among the most challenging research problems is the development of a transaction model in the presence of so called composite events. Our approach of multi-parent subtransactions tries to fill this gap. Multi-parent subtransactions extend the well-known nested transaction model by allowing multiple transactions to start a subtransaction in cooperation. In particular, this paper discusses the impacts of our extensions on the locking protocol of the original nested transaction model. Keywords and Phrases....