IBM Systems Journal

This paper presents a conceptual model of an event-processing network for expressing the event-based interactions and event-processing specifications among components. The model is based on event-driven architecture, a pattern promoting the production, detection, consumption, and reaction to events. The motivation is the lack of standardization in the areas of configuring and expressing the event-processing directives in event-driven systems. Some existing approaches are through Structured Query Language, script languages, and rule languages, and are executed by standalone software, messaging systems, or datastream management systems. This paper provides a step toward standardization through a conceptual model, making it possible to express event-processing intentions independent of the implementation models and executions. It is a unified model serving as a metamodel to these existing approaches.

We apply pattern language methodology to describe design and integration patterns for real-world-aware and real-time solutions, i.e., software solutions that integrate business information processing with sensor and actuator manipulations of the external world. Efficient engineering of such solutions depends on the definition and reuse of components whose real-time characteristics can be specified. Other nonfunctional characteristics, such as throughput and reliability, may also be constrained and critical for correct behavior of a design element. We present a pattern language comprising a basic catalog of design patterns for component-based real-time solutions.

This special issue of the IBM Systems Journal focuses on responsive systems, a term in which we include real-time and event-based systems. A realtime system is a computing system subject to constraints on the interval from the occurrence of an external event until the system response. A real-time constraint can be hard, in which case failure to complete the required computation before the deadline amounts to a system failure, or it can be soft, in which case delayed responses are tolerated but viewed as lowering the quality of the service provided by the system. An event-based system is a computing system whose components operate in response to events. The events processed by a component can be either external to the system or they can be generated by another component.

All too often, software designers ignore the fact that a running computer system is a combination of software and hardware. In this combination, hardware may play a crucial role, particularly in time-sensitive systems. In this paper, we first explore the nature and impact that platforms may have on application software and its design. Based on this analysis, a canonical model of software platforms is proposed to assist in more accurately factoring in the effects of platforms on the design of real-time and embedded software applications. Finally, we show how this model can be realized using modern model-driven design standards and methods.