Software engineering and middleware: a roadmap

The construction of a large class of distributed systems can be simplified by leveraging middleware, which is layered between network operating systems and application components. Middleware resolves heterogeneity, and facilitates communication and coordination of distributed components. Existing middleware products enable software engineers to build systems that are distributed across a local-area network. State-of-the-art middleware research aims to push this boundary towards Internet-scale distribution, adaptive and reconfigurable middleware and middleware for dependable and wireless systems. The challenge for software engineering research is to devise notations, techniques, methods and tools for distributed system construction that systematically build and exploit the capabilities that middleware deliver. 1 I N T R O D U C T I O N Various commercial trends have lead to an increasing demand for distributed systems. Firstly, the number of mergers between companies is continuing to increase. The different divisions of a newly merged company have to deliver unified services to their customers and this usually demands an integration of their IT systems. The time available for delivery of such an integration is often so short that building a new system is not an option and therefore existing system components have to be integrated into a distributed system that appears as an integrating computing facility. Secondly, the time available for providing new services are decreasing. Often this can only be achieved if components are procured off-the-shelf and then integrated into a system rather than built from scratch. Components to be integrated may have incompatible requirements for their hardware and operating system platforms; they have to be deployed on different hosts, forcing the resulting system to be distributed. Finally, the Internet provides new opportunities to offer products and services to a vast number of potential customers. In this setting, it is difficult to estimate the scalability requirements. Permission to make digital or hard copies of all or part of this work lbr personal or classroom use is granted without fee provided that copies are not made or distributed tbr profit or commercial advantage and that copies bear this notice and the lull citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a tee. Future of Sofware Engineering Limerick Ireland Copyright ACM 2000 1-58113-253-0/00/6...$5.00 An e-commerce site that was designed to cope with a given number of transactions per day may suddenly find itself exposed to demand that is by orders of magnitude larger. The required scalability cannot usually be achieved by centralized or client-server architectures but demands a distributed system. Distributed systems can integrate legacy components, thus preserving investment, they can decrease the time to market, they can be scalable and tolerant against failures. The caveat, however, is that the construction of a truly distributed systems is considerably more difficult than building a centralized or client/server system. This is because there are multiple points of failure in a distributed system, system components need to communicate with each other through a network, which complicates communication and opens the door for security attacks. Middleware has been devised in order to conceal these difficulties from application engineers as much as possible; As they solve a real problem and simplify distributed system construction, middleware products are rapidly being adopted in industry [6]. In order to build distributed systems that meet the requirements, software engineers have to know what middleware is available, which one is best suited to the problems at hand, and how middleware can be used in the architecture, design and implementation of distributed systems. The principal contribution of this paper is an assessment of both, the state-of-the-practice that current middleware products offer and the state-of-the-art in middleware research. Software engineers increasingly use middleware to build distributed systems. Any research into distributed software engineering that ignores this trend will only have limited impact. We, therefore, analyze the influence that the increasing use of middleware should have on the software engineering research agenda. We argue that requirements engineering techniques are needed that focus on non-functional requirements, as these influence the selection and use of middleware. We identify that software architecture research should produce methods that guide engineers towards selecting the right middleware and employing it so that it meets a set of non-functional requirements. We then highlight that the use of middleware is not transparent for system design and that design methods are needed that address this issue.