, 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...

This paper presents a framework for the formal specification of active database systems, and shows how the framework can be used to describe the functionality of three well known example systems, namely Starburst, POSTGRES and Ariel. The framework has been developed using Object-Z to structure specifications in a way that emphasises commonalities and key differences between the designs, and that is readily extensible to support new constructs and systems. Such a formal framework can be used to provide formal descriptions of systems that have previously been described only informally, to compare the functionalities of different systems by contrasting support for fundamental concepts, and as a basis for reasoning about rule bases in the context of different active rule systems. The paper also demonstrates the applicability of objectoriented formal methods to the specification of advanced database functionality. 1 Introduction Active database systems have been proposed to support databas...

NASA's Numerical Aerodynamic Simulation (NASI Program has completed development of the initial operating configuration of the NAS Processing System Network (NPSN). This is the first milestone in the continuing and pathfinding effort to provide state-of-the-art supercomputing for aeronautics research and development. The NPSN, available to a nation-wide community of remote users, provides a uniform UNIX 1 environment over a network of host computers ranging from the new Cray-2 supercomputer to advanced scientific workstations. This system, coupled with a vendor-independent base of common user interface and network software, presents a new paradigm for supercomputing environments. Presented here is the background leading to the NAS Program, its programmatic goals and strategies, technical goals and objectives, and the development activ-ities leading to the current NPSN configuration. Program status, near-term plans and plans for the next major milestone, the extended operating configura-tion, are also discussed.

Reactivity, the ability to detect simple and composite events and respond in a timely manner, is an essential requirement in many present-day information systems. With the emergence of new, dynamic Web applications, reactivity on the Web is receiving increasing attention. Reactive Web-based systems need to detect and react not only to simple events but also to complex, real-life situations. This paper introduces XChange, a language for programming reactive behaviour on the Web, emphasising the querying of event data and detection of composite events.