Computing and Information Systems - Research Publications
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ItemModelling ODP viewpoints(ACM Press, 1994)This paper gives a brief insight into the current work on the development of an architectural semantics for Open Distributed Processing (ODP). It first provides an introduction to the work on the formalisation in LOTOS and Z of the basic modelling and specification concepts of Part 2, and then focuses on the viewpoint languages of Part 3 of the Basic Reference Model for ODP (RM-ODP). It also shows up the separation of concerns that is achieved through these viewpoints thereby enabling systems to be considered from aspects which might be of interest to different people. This paper also highlights the way in which conformance between these formalised viewpoints can be checked, thereby ensuring that the system as a whole is consistent with the system as a collection of abstract viewpoints of the system. Finally the paper concludes with a brief discussion on the advantages and disadvantages of LOTOS and Z for modelling viewpoint languages and the RM-ODP generally.
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ItemBusiness-oriented development of telecommunication services(Association for Computing Machinery, 1998)The development of software for distributed systems, e.g. telecommunication services, is a complex activity. Numerous issues have to be resolved when developing such systems, examples of which are language/system heterogeneity and remoteness of components. Interface definition languages (IDLs) are used as the basis for addressing some of these issues. IDLs allow for the specification of the syntactic aspects of the interfaces of the components in the system to be made. Whilst lending itself to issues of heterogeneity and location transparency, dealing with IDL as the basis for system development is not without its problems. Two of the main problems with IDL are its lack of behaviour and its lack of abstraction. Thus designers should not be constrained to work within the syntactic notations used to implement their systems, nor should they be unaided in how they might better design their systems. In this paper we show how these issues are being addressed in the TOSCA project in its development of a service creation and validation environment.
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ItemEngineering telecommunication services with SDL(Kluwer Academic, 1999)If formal techniques are to be more widely accepted then they should evolve as current software engineering approaches evolve. Current techniques in the development of distributed systems use interface definition languages (IDLs) as a basis for the underlying communication and also as an abstraction tool. Object-oriented technologies and the idea of engineering software through frameworks are also widely accepted approaches in developing software. In this paper we show how the formal specification language SDL and associated tool support have been applied in the TOSCA project to engineer telecommunication services using these current techniques.
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ItemType checking in open distributed system: a complete model and its Z specification(Chapman & Hall on behalf of the International Federation for Information Processing (IFIP), 1997)Type checking is at the heart of distributed systems. The ability to be able to configure objects and have them interwork correctly may well be regarded as the fundamental issue in the development of reliable distributed systems. The type system put forward in the current standardisation activity of Open Distributed Processing (ODP), however, is both and incorrect. The inadequacy is due to the scope of the type system being based entirely on syntactic issues. To achieve reliable interoperability between systems, a type system should deal with behavioural (semantic) issues as well as non-functional issues, aspects of the type that its signature and behaviour do not capture. The incorrectness is due to the syntactic issues not being dealt with correctly. That is, clients and servers have fundamentally different type rules that apply to them. We provide a Z specification of a robust type system that deals with the syntactic aspects of types (correctly) as well as a treatment of the behavioural and non-functional aspects of types.
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ItemCreating telecommunication services based on object-oriented frameworks and SDL(IEEE Computer Society, 1999)This paper describes the tools and techniques being applied in the TINA Open Service Creation Architecture (TOSCA) project to develop object-oriented models of distributed telecommunication services in SDL. The paper also describes the way in which Tree and Tabular Combined Notation (TTCN) test cases are derived from these models and subsequently executed against the CORBA-based implementations of these services through a TTCN/CORBA gateway.
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ItemSpecifying multimedia configurations in Z(IEEE Computer Society, 1999)In this paper we illustrate how the formal specification language Z can be used to reason about the temporal and throughput constraints associated with multimedia flows of information. In particular we show how it is possible to specify issues related to maximum delays, throughputs and jitter of information flows and how control of these flows can be achieved. What makes out work particularly interesting is that we deal with temporal aspects of systems without the use of a temporal logic. Rather, we highlight the versatility of the Z language in modelling systems with real time constraints.
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ItemSpecifying aspects of multimedia in LOTOS(IEEE Computer Society, 1999)The formal specification language LOTOS provides a model of systems where the temporal ordering of actions is specified. LOTOS typically does not deal with the specific times at when actions can occur. Most approaches for specifying real time systems in LOTOS have either extended the language, e.g. with timing aspects, or used the language in conjunction with a temporal logic. We argue that such approaches are not always necessary and that LOTOS is much more flexible than sometimes claimed. To support our arguments we show how LOTOS can be used to specify a multitude of timing issues that can be associated with the production and consumption of multimedia flows.
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ItemEngineering of interworking TINA-based telecommunication services(IEEE Computer Society, 1999)This paper describes a Service Creation approach being developed in the EU funded ACTS TOSCA (TINA Open Service Creation Architecture) project to rapidly develop validated TINA based multimedia telecommunications services. The approach is based around object-oriented software frameworks in SDL which are specialized towards services by means of graphical paradigm tools. Further, in TOSCA, the need for service interworking across service provider domains via federation has been recognized in order to allow users to join service sessions offered by providers they are not customers of. However, service interworking may cause undesired behavior - the so called service interaction phenomenon. This paper focuses on this issue and the underlying technology of the service creation approach with emphasis on how service federation has been implemented.