A specification architecture for multimedia systems in Open Distributed Processing

A next generation of systems that should appear will have to manage simultaneously several geographically distributed users. These systems belong to the class of computer-supported cooperative work systems (CSCW). The development of such complex systems requires rigorous development methods and flexible open architectures. Open distributed processing (ODP) is a standardization effort that aims at providing such architectures. ODP features appropriate abstraction levels and a clear articulation between requirements, programming and infrastructure support. ODP advocates the use of formal methods for the specification of systems and components. The computational model, an object-based model, one of the abstraction levels identified within ODP, plays a central role in the global architecture. In this model, basic objects can be composed with communication and distribution abstractions (called binding objects) to form a computational specification of distributed systems, or applications. Computational specifications can then be mapped (in a mechanism akin to compilation) onto an engineering solution. We use an ODP-inspired method to computationally specify a cooperative system. We start from a general purpose component that we progressively refine into a collection of basic and binding objects. We focus on two issues of a co-authoring application, namely, dynamic reconfiguration and multiview synchronization. We discuss solutions for these issues and formalize them using the MT-LOTOS specification language that is currently studied in the ISO standardization formal description techniques group.

Recent developments in high-speed networks and highperformance workstations have led to the emergence of a new class of applications termed distributed multimedia applications. However, the range of distributed systems architectures currently being proposed to support open systems integration were largely conceived prior to these developments. Initial work directed towards the introduction of multimedia in environments compatible with ISO's Open Distributed Processing (ODP) standard has suggested that significant developments to the underlying architecture are required. These developments are now being reflected in new versions of the ODP standard. However, OSF's Distributed Computing Environment (DCE), currently emerging as a de-facto standard for distributed processing, does not fully address the requirements of multimedia computing. This paper reports on the impact that multimedia has had on the ODP community and examines how the community's experiences can be used as a basis for incorporating multimedia in DCE.KeywordsMultimedia ApplicationRemote Procedure CallDistribute Computing EnvironmentContinuous InterfaceBinding InformationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

This paper presents a translation between the formal description technique LOTOS and the object-oriented specification language Object-Z. The need for such a translation lies in the use of formal methods in viewpoint specification, and in particular in the Open Distributed Processing standard. The use of viewpoints as a set of partial interlocking specifications brings an obligation to check the consistency of these partial specifications, and to do so we need to relate specifications written in differing languages. The work presented here supports the consistency checking of viewpoints written using formal methods by defining a translation from full LOTOS to Object-Z. A common semantic model is provided for the languages, and we verify the translation with respect to this model. The translation is illustrated with a small example.

Distributed multimedia information systems require a range of different interaction styles ranging from simple remote operation interaction to complex patterns of interaction involving both discrete and continuous data. The standardized reference model for Open Distributed Processing (ODP) defines a binding model that encapsulates different interaction styles within explict binding objects. In this paper we introduce the idea of using a trading model for selecting potential binding types. In this scheme a set of binding factories are located based on a specification of the required properties of the binding. The located set of binding factories are all capable of instantiating binding objects with properties conforming to those specified by the client.Key wordsMultimediaQoSTypingODP

This paper discusses the issues of specification style and refinement that arise in connection with viewpoint modelling. In particular, we consider the support needed in order to deal with viewpoints at different levels of abstraction. The motivation for this work arises from the use of viewpoints in distributed systems design, in particular the Open Distributed Processing standard. Full proceedings of the workshop it was presented at can be found on WWW: A. Finkelstein and G. Spanoudakis (eds.): http://web.soi.city.ac.uk/homes/gespan/VP F SE.html, ACM SIGSOFT Foundations of Software Engineering 4, 1996.

Decision procedures are presented for checking a small but useful class of properties for any finite-state system consisting of real-time discrete-event processes. A timed transition model (TTM) is used for representing real-time discrete-event processes, and real-time temporal logic (RTTL) is the assertion language in which the property to be verified is stated. The relationship of TTMs to other formalisms is summarized along with a complete definition of TTMs and an overview of RTTL. The construction of reachability graphs is discussed, two different procedures are presented for constructing reachability graphs, and the corresponding decision procedures are given. >

Areas of computer application are being broadened rapidly due to the rapid improvement of the performance of computer hardware. Applications that were not feasible before are now becoming feasible with high-performance computers. This results in increased demands for computer applications that are large and have complex temporal characteristics. Most analysis methods available, however, cannot handle large, complex real-time systems adequately; They do not scale-up, lack formalism to represent complex features and perform analyses with mathematical rigor, do not support analyses from different viewpoints, or are too hard to learn and apply. TVe need analysis methods that support formal specification and verification of real-time systems. Incremental performance of specification and analysis of systems from different viewpoints (e.g., user, analyst ) must also be supported with languages appropriate for each different viewpoint and for the users involved. This paper introduces a real-time systems analysis method, named PARTS, that aims at providing above features. PARTS supports analyses from two viewpoints: external viewpoint, a view of the sys-Permission tern from the user's perspective, and internal viewpoint, a view from the developer's perspective. These viewpoints are specified using formal languages, which are: Real-Time Events Trace (RTET) for the external viewpoint, and Time Enriched Statecharts (TES) and PARTS Data Flow Diagram (PDFD) for the internal viewpoint. All PARTS languages are based on the Real-Time Temporal Logic (RTTL), and consistency of the specifications made from two different viewpoints are analyzed based on the same RTTL formalism. PARTS converts RTET and TES specifications to RTTL specifications, which are then integrated and analyzed for consistency. All of the PARTS specificaticm languages support the top-down strategy to handle complexity.

Responsive communication protocols must incorporate both real-time and fault-tolerant properties. In this paper, we propose a new method for detecting design faults in specifications of responsive communication protocols based on real-time temporal logic. We also present a case study where a connection establishment protocol for a plant control system is dealt with.

In this paper, we introduce a real-time temporal knowledge logic, called RTKL, which is a combination of real-time temporal logic and knowledge logic. It is showed that temporal modalities such as “always in an interval”, “until in an interval”, and knowledge modalities such as “knowledge in an interval” and “common knowledge in an interval” can be expressed in such a logic. The model checking algorithm is given. Furthermore, we add cooperation modalities to RTKL and get a new logic RATKL, which can express not only real-time temporal and epistemic properties but also cooperation properties. The model checking algorithm for RATKL is also given.

In this paper, a formal model of Event-Driven Nets (EDNs) is presented. Real-time temporal logic is used for representing both the behavior and structure of a modelled net. The structure of the net is defined using a set of executable predicates formed over state and pulse temporal variables. Considering this formal model, we outline an implementation of an interpretation technique for the EDN structural description. Finally, the modelling power of EDNs is demonstrated by the behavioral and performance simulation of a simple distributed computer system.

A (possibly infinite-state) real-time discrete-event plant is modeled as a timed transition system. The free (uncontrolled) behavior of the plant is usually unsatisfactory in some important respect. A specification (written in real-time temporal logic) of required plant behavior is therefore to be imposed on the plant. The key result is a controller development procedure which shows how to systematically develop control strategies for a class of safety properties. The procedure isolates the unsafe part of the behavior, and gives a set of conditions under which the unsafe behavior can be made safe. If the conditions are satisfied, then the plant is guaranteed to satisfy the required specification. The states of the system are not explicitly represented in the design procedure; instead, predicates and predicate transformers, are used to overcome some of the problems of combinatorial explosion of states in large systems. >

Multimedia synchronization is the essential technology for the integration of multimedia in distributed multimedia systems. The multimedia synchronization model has been recognized by many researchers as a premise of the implementation of multimedia synchronization. In distributed multimedia systems, the characteristic of multimedia synchronization is dynamic, and the key medium has the priority in multimedia synchronization. The previously proposed multimedia synchronization models cannot meet these requirements. So a new multimedia dynamic synchronization model—DSPN, based on the timed Petri-net has been designed in this paper. This model can not only let the distributed multimedia system keep multimedia synchronization in a more precise and effective manner according to the runtime situation of the system, but also allow the user to interact with the presentation of multimedia.

The Session Initiation Protocol is used for establishing peer-to-peer sessions with one or more participants. Internet telephone calls, multimedia distribution, conference calls, and multiplayer online games are examples of these sessions. Since formal description is the first step of modeling and analysis of a system, this paper reviews formal descriptions of this protocol and suggests ideas to build more realistic model.

This paper presents an approach for the specifications of the configurable distributed systems, which is based on the computational model with information transport ports. Features of the approach are demonstrated with the help of a reference example. Fragments of the system architects' language are presented which illustrate the flexibility of the approach and its wide areas of application. Examples of specifications for ATM and distributed multimedia systems are shown.

A window-assisted video partitioning strategy for partitioning and caching video streams in distributed multimedia systems