Categories for Software Engineering (PDF)

controlled. For that purpose, we need first-class representations of the interconnections. This level of complexity is aggravated by the need to evolve systems. As the world of business in general becomes more and more aggressive and competitive, for instance, as a consequence of the impact of the Internet and wireless technologies, companies need their information systems to be easily adaptable to changes in the business rules with which they operate, most of the time in a way that does not imply interruptions to the services that they provide. Quoting directly from [47], "... the ability to change is now more important than the ability to create e-commerce systems in the first place.

Change becomes a first-class design goal and requires business and technology architecture whose components can be added, modified, replaced and reconfigured". All this means that the "complexity" of software has definitely shifted from construction to evolution, and that methods and technologies are required that address this new level of complexity and adaptability.

Software architecture [50, 88] is a "recent" topic in software engineering aimed at addressing the gross decomposition and organisation of systems in which, through so-called connectors, component interactions are recognised as being first-class design entities [98]. According to [2], a connector (type) can be defined by a set of roles and a glue specification. For instance, a typical client-server architecture can be captured by a connector type with two roles - client and server - that describe the expected behaviour of clients and servers, and a glue that describes how the activities of the roles are coordinated (e.g. asynchronous communication between the client and the server).

The roles of a connector type can be instantiated with specific components of the system under construction, which leads to an overall system structure consisting of components and connector instances establishing the interactions between the components. The similarities between architectural constructions as informally described above and parameterised programming [56] are rather striking and have been developed in [59] in the context of the emerging interest in software architecture. The view of architecture that is captured by the principles and formalisms of parameterised programming is reminiscent of module interconnection languages and interface definition languages [55].