Configuring Heterogeneous And Open Systems S. Cheung, S. Crane, N. Dulay, J. Kramer, J. Magee, M. Sloman, K. Twidle Department of Computing, Imperial College 180 Queen's gate, London SW7 2BZ email: mss@doc.ic.ac.uk Abstract This paper describes a configuration approach to integrating heterogeneous software components which communicate and interact in an open distributed system. The Rex configuration facilities support both building of an initial system, early binding, and the subsequent dynamic reconfiguration of the running system, late binding. This configuration approach involves the use of a separate configuration language (DARWIN) to specify a system in terms of the instances of component types; the interconnection between component interfaces; and the mapping of software to hardware. Applications are constructed using hierarchical structure composition of simpler components. Changes to a system can be easily understood and formulated in terms of adding or removing component types, instances and interconnections. Heterogeneity of software components is achieved by using an Interface Specification Language which specifies the interactions between the components. The ISL has language specific varients designed to complement the language and can be translated to and from a common Structural Type Representation. This provides the basic level for validating component binding at both the early and late binding stages. The STR is also used to transform messages passed across heterogeneous boundaries and to monitor those messages for eg. debugging purposes. Configuration domains are used to perform application navigation. A domain is a name scope in which references to instance interfaces can be registered and resolved. Servers can register themselves or be registered by a manager along with other attributes that describe the service. Clients can locate the servers either by requesting a suitable specification of a required service (trading) or by using the name of the server instance. This may be compared with the ANSA trader and TCP/IP DNS. ----- Kevin Twidle G8RKU Tel: +44 71 589 5111 x5068 Fax: +44 71 581 8024 Dept of Computing, Imperial College, 180 Queen's Gate, London SW7 2BZ, England Email: kpt@doc.ic.ac.uk, kpt%uk.ac.ic.doc@nsfnet-relay.ac.uk, ..!ukc!icdoc!kpt "It's not the cough that carries you off, it's the coffin they carry you off in"