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Many would argue that future breakthroughs in software productivity will depend on our ability to combine existing pieces of software to produce new applications. An important step towards this goal is the development of new techniques to detect and cope with mismatches in the assembled parts. Some problems of composition are due to low-level issues of interoperability, such as mismatches in programming languages or database schemas. However, in this paper we highlight a different, and in manywaysmore pervasive, class of problem: architectural mismatch. Specifically, we use our experience in building a family of software design environments from existing parts to illustrate a variety of types of mismatch that center around the assumptions a reusable part makes about the structure of the application in which is to appear. Based on this experience we show how an architectural view of the mismatch problem exposes some fundamental, thorny problems for software composition and suggests poss...

In this paper we introduce the concept of continual queries, describe the design of a distributed event-driven continual query system -- OpenCQ, and outline the initial implementation of OpenCQ on top of the distributed interoperable information mediation system DIOM [21, 19]. Continual queries are standing queries that monitor update of interest and return results whenever the update reaches specified thresholds. In OpenCQ, users may specify to the system the information they would like to monitor (such as the events or the update thresholds they are interested in). Whenever the information of interest becomes available, the system immediately delivers it to the relevant users; otherwise, the system continually monitors the arrival of the desired information and pushes it to the relevant users as it meets the specified update thresholds. In contrast to conventional pull-based data management systems such as DBMSs and Web search engines, OpenCQ exhibits two important featu...

As the design of software architectures emerges as a discipline within software engineering, it will become increasingly important to support architectural description and analysis with tools and environments. In this paper we describe a system for developing architectural design environments that exploit architectural styles to guide software architects in producing specific systems. The primary contributions of this research are: (a) a generic object model for representing architectural designs; (b) the characterization of architectural styles as specializations of this object model; and (c) a toolkit for creating an open architectural design environment from a description of a specific architectural style. We use our experience in implementing these concepts to illustrate how style-oriented architectural design raises new challenges for software support environments.

There is increasing interest in having software systems execute and interoperate over the Internet. Execution and interoperation at this scale imply a degree of loose coupling and heterogeneity among the components from which such systems will be built. One common architectural style for distributed; loosely-coupled, heterogeneous software systems is a structure based on event generation, observation and notification. The technology to support this approach is well-developed for local area networks, but it is illsuited to networks on the scale of the Internet. Hence, new technologies are needed to support the construction of large-scale, event-based software systems for the Internet. We have begun to design a new facility for event observation and notification that better serves the needs of Internet-scale applications. In this paper we present results from our first step in this design process, in which we defined a framework that captures many of the relevant design dimensions. Our framework comprises seven models-an object model, an event model, a naming model, an observation model, a time model, a notification model, and a resource model. The paper discusses each of these models in detail and illustrates them using an example involving an update to a Web page. The paper also evaluates three existing technologies with respect to the seven models.

Software architects use a number of commonly-recognized “styles” to guide their design of system structures. Each of these is appropriate for some classes of problems, but none is suitable for all problems. How, then, does a software designer choose an architecture suitable for the problem at hand? Two kinds of information are required: (1) careful discrimination among the candidate architectures and (2) design guidance on how to make appropriate choices. Here we support careful discrimination with a preliminary classification of styles. We use a two-dimensional classification strategy with control and data issues as the dominant organizing axes. We position the major styles within this space and use finer-grained discriminations to elaborate variations on the styles. This provides a framework for organizing design guidance, which we partially flesh out with rules of thumb.

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this paper I briefly outline and compare three approaches to providing such a basis. 2. Basic Properties

Implicit invocation or publish-subscribe has become an important architectural style for large-scale system design and evolution. The publish-subscribe style facilitates developing large-scale systems by composing separately developed components because the style permits loose coupling between various components. One of the major bottlenecks in using publish-subscribe systems for very large scale systems is the efficiency of filtering incoming messages, i.e., matching of published events with event subscriptions. This is a very challenging problem because in a realistic publishsubscribe system the number of subscriptions can be large. In this paper we present an approach for matching published events with subscriptions which scales to a large number of subscriptions. Our approach uses Binary Decision Diagrams, a compact data structure for representing boolean functions which has been successfully used in verification techniques such as model checking. Experimental results clearly demonstrate the efficiency of our approach.