Blair, G., Blair, L., Bowman, H., Chetwynd, A.: Formal Specification of Distributed Multimedia Systems. University College London Press (1997)  Home/Search   Document Not in Database   Summary   Related Articles   Check

....description will enable performance aspects to be addressed. Work that is relevant to the performance issues includes analytic approaches using formal methods (e.g. model checking probabilistic and real time automata [17] 13] and the dual language approaches to QoS specification and validation [18]. Model checking represents perhaps the most feasible approach to large scale verification. Dual language approaches provide a means to separate out the specification of QoS requirements from the description of the underlying resource. The latter fits well with the simulation models which can be ....

G. Blair, L. Blair, H. Bowman, and A. Chetwynd, Formal Specification of Distributed Multimedia Systems: University College London Press, 1997.

....Their behaviour is specified in formal timed automata descriptions. One of the advantages of using automata is that we can reason about and simulate their behaviour. This, together with a formal description of the complete system can be used to simulate and formally reason about the whole system [11, 12]. A more detailed quality of service management example can be found in [13] This also includes a detailed evaluation of the approach. 8 Producer Binding Buffer Consumer Monitor M Strategy selector S C Strategy activator P Strategy activator Composition meta object Encapsulation ....

Gordon Blair, Lynne Blair, Howard Bowman, and Amanda Chetwynd. Formal Specification of Distributed Multimedia Systems. UCL Press, 1998.

....r, Trevor Jones, Gordon B l a i r 1 Abstract 1. Introduction In our previous work, we have been interested in the development of methodologies and techniques for the specification and verification of distributed multimedia systems, with particular emphasis on object and component based systems [Blair98a]. This has led us to develop an aspect oriented style of specification that follows the principles of aspect oriented programming [AOP00] Murphy99] Essentially, we decompose a system specification into four aspects: functional, non functional, management and requirements. Motivations for this ....

G.S. Blair, L. Blair, H. Bowman, A. G. Chetwynd, "Formal Specification of Distributed Multimedia Systems", London: UCL Press, 1998.

....the local clocks) The finiteness of the transition systems associated with IP processes can be useful for automatic verification. In the rest of this paper we apply our framework on a couple of classical examples: The Mine Pump taken from [19] and The Lip Synchronization Problem taken from [5]. 3 The Mine Pump Water percolating into a mine is collected in a sump to be pumped out of the mine. The water level sensors, Sensor D and Sensor E, detect when water is above a high and a low level respectively. A pump controller switches the pump on when the water reaches the high water level ....

Blair,G.S., Blair,L., Bowman,H., Chetwynd,A.: Formal Specification in Distributed Multimedia Systems. University College London Press (1997).

....paper, is to achieve the acceptably synchronized presentation of a sound and a video stream, which are sent separately over a network to a presentation device. The protocol is a standard example from the multimedia domain and has been investigated with various formalisms [SHH92, Reg93, ABSS96, BBBC98] In detail the requirements are as follows [BFK 98] ffl A sound frame must be presented every 30 milliseconds (ms) ffl Video frames should be presented 35 to 45 ms after one another. Furthermore, video frames may lag sound by no more than 150 ms and may precede sound by no more than 15 ....

G. Blair, L. Blair, H. Bowman, and A. Chetwynd. Formal Specification of Distributed Multimedia Systems. UCL Press, 1998.

....new concept, but are referred to under different names depending on the audience. For example, Kiczales aspects [17] Zave and Jackson s multi paradigm approach [24] ODP s viewpoints [21] 8] Finkelstein and Spanoudakis perspectives [13] and our earlier work based on a separation of concerns [4] are all, at heart, addressing the same issue: the structuring of large and complex software systems. A key advantage of such an approach is that the overall system behaviour can be subdivided into different aspects (or viewpoints, perspectives, etc. each of which is specified separately. ....

....multimedia systems. Consequently, we adopt the use of the (standardised) formal description technique LOTOS [10] for an abstract specification of the functional behaviour. For the second aspect, QoS parameters, in previous work we have developed and evaluated a real time temporal logic, QTL [4]. In this work, we were primarily concerned with timeliness properties such as latency, throughput and jitter. However, the need for another category of QoS, namely reliability properties, led us to develop a stochastic extension to QTL, called SQTL [18] Consequently, we propose the use of a ....

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G.S. Blair, L. Blair, H. Bowman, A. G. Chetwynd, "Formal Specification of Distributed Multimedia Systems", London: UCL Press, 1998.

....Long Term Research Project 24962 scription lack expressiveness for two issues raised by multimedia applications: the compatibility of protocols used for transferring data streams (e.g. specialization) and the verification of the application timeliness. The second issue has been addressed in [8, 1]. However, their solutions rely on mathematical models that are either too formal or too empirical. In [8] the temporal behavior of the application is computed only by relying on formal distributions. While this method is easily applicable to a limited set of distributions, it turns out to be a ....

....set of distributions, it turns out to be a tedious, even impossible task when arbitrary formal distributions need to be composed. A convincing example is given by the determination of the distribution of the maximum of any two arbitrary normal distributions. The mathematical model proposed in [1] relies on a simulation of the temporal behavior of the application and thus leads to the opposite problem. This model requires that whenever a group of elements is reused, the temporal verification tool has to simulate the global behavior of the application on a per element basis. In this paper, ....

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G. Blair, L. Blair, H. Bowman, and A. Chetwynd. Formal Specification of Distributed Multimedia Systems. UCL Press, 1998.

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Blair, G., Blair, L., Bowman, H., Chetwynd, A.: Formal Specification of Distributed Multimedia Systems. University College London Press (1997)

.... been proposed with the more general aim of addressing the problem of structuring large and complex software systems, e.g. aspects [Kiczales97] multi paradigm approaches [Zave96] Blair99a] viewpoints [Boiten96] perspectives [Finkelstein96] and our earlier work based on a separation of concerns [Blair98a]. Such techniques, by their very nature, require different paradigms for different aspects (respectively viewpoints, perspectives, etc. So, for example, case studies in Zave and Jackson s approach make use of the rich, yet diverse, nature of languages such as logic (including ordinary predicate ....

G.S. Blair, L. Blair, H. Bowman, A. G. Chetwynd, "Formal Specification of Distributed Multimedia Systems", London: UCL Press, 1998.

....automata and the associated tool suite. 1. INTRODUCTION In our previous work, we have been interested in the development of methodologies and techniques for the specification and verification of distributed multimedia systems, with particular emphasis on object and component based systems [Blair98a]. This has led us to develop an aspectoriented style of specification that follows the principles of aspect oriented programming [AOP00] Murphy99] Essentially, we decompose a system specification into four aspects: functional, non functional, management and requirements. Motivations for this ....

G.S. Blair, L. Blair, H. Bowman, A. G. Chetwynd, "Formal Specification of Distributed Multimedia Systems", London: UCL Press, 1998.

.... A number of different techniques have been proposed with the more general aim of addressing the problem of structuring large and complex software systems, e.g. aspects [17] multiparadigm approaches [28] 5] viewpoints [8] perspectives[12] and our earlier work based on a separation of concerns[3]. Such techniques, by their very nature, require different paradigms for different aspects (viewpoints, perspectives, etc. So, for example, case studies in Zave and Jackson s approach make use of the rich, yet diverse, set of languages such as logic (including ordinary predicate logic, first ....

G.S. Blair, L. Blair, H. Bowman, A. G. Chetwynd, "Formal Specification of Distributed Multimedia Systems", London: UCL Press, 1998.

....Their behaviour is specified in formal timed automata descriptions. One of the advantages of using automata is that we can reason about and simulate their behaviour. This, together with a formal description of the complete system can be used to simulate and formally reason about the whole system [24, 25]. 7 Concluding remarks This paper has presented OOPP, the Open ORB Python Prototype. OOPP implements a reflective component based middleware platform with support for quality of service management. The paper focused on the programming model and the meta models provided by OOPP. OOPP implements ....

G. Blair, L. Blair, H. Bowman, and A. Chetwynd, Formal Specification of Distributed Multimedia Systems. UCL Press, 1998.

....of the capabilities and the practical use of formal notations and their associated tools with small size experiments. 2 A Simple Media Stream The most basic requirement for supporting multimedia is to be able to define continuous flows of data; such structures are typically called media streams [4]. In this paper, we will discuss and illustrate a number of aspects related to media constraint modeling using such a multimedia stream. The basic media stream is as depicted in figure 1. It has three top level components: a Source, a Sink and a communication Medium (which we will from now on ....

....communication actions support the flow of data (see figure 1 again) sourceout , sinkin and play , which respectively transfer packets from the Source to the Medium, from the Medium to the Sink and display them at the Sink. Formal descriptions of media streams have been given before, e.g. [4] etc. However to our knowledge, no formal verifications have been performed. This is one contribution of this paper. The following informal description of the behaviour of the stream is kept similar to the LOTOS QTL specification that appears in [4] All communication between the Source and ....

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G.S. Blair, L. Blair, H. Bowman, and A. Chetwynd. Formal Specification of Distributed Multimedia Systems. University College London Press, September 1997.

....of more quantitative aspects (such as time and probabilities) is not possible. For example, in distributed multimedia systems, quality of service parameters such as throughput, latency, jitter and percentage error loss require realtime and probabilistic extensions to the above process algebra [Blair98a]. Many such extensions have been proposed, for example, Enhanced Timed LOTOS (ET LOTOS) Leonard97] and Timed Probabilistic CCS (TPCCS) Hansson91] For the modelling of stochastic systems (where events occur at a time determined by a random variable) stochastic process algebra have also been ....

....aspects to be written in the same language. Consequently, we will use the process algebra LOTOS for an abstract specification of functional behaviour. For the quantitative aspects (performance constraints) we have evaluated real time and probabilistic temporal logic in our previous research (see [Blair98a] and [Lakas96a] We will continue with our use of temporal logic in this paper. To clarify terminology, by performance constraints, we mean characteristics of the actual system that cannot be defined purely in functional terms. Examples of such constraints include timeouts, the assumed ....

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G.S. Blair, L. Blair, H. Bowman, A. G. Chetwynd, " Formal Specification of Distributed Multimedia Systems" , London: UCL Press, 1998.

.... can be found in the literature under various names, e.g. aspect oriented programming [Lopes98] Zave and Jackson s multi paradigm approach [Zave96] ODP s viewpoints [ISO95] Boiten96] Finkelstein and Spanoudakis perspectives [Finkelstein96] and our earlier work based on a separation of concerns [Blair98a]. It is the first two of these that relate most directly to our work. In the former, a system can be thought of as a collection of different aspects, each of which is programmed separately and, if appropriate, in different languages. Once written, the different aspects can be woven together (using ....

....and only one action is permitted in each state of the underlying timed state sequences (although more than one state, hence action, can occur at a given time) A brief syntactic description of the logic is given below. For a more detailed description of our logic, we refer the reader to [Blair98a]. f : a false f 1 f 1 O d f f 1 U d f 2 where a is an action (in a LOTOS like style as described informally above) d (including 0) 4 01 06 99 Note that the propositional operators not ( and ( and or ( can be derived in the usual way from implies ( and ....

G.S. Blair, L. Blair, H. Bowman, A. G. Chetwynd, "Formal Specification of Distributed Multimedia Systems", London: UCL Press, 1998.

....is the need to ensure timely transmission and presentation of multimedia data, e.g. ensuring that the end to end timing delay between transmitting and presenting video frames stays within acceptable bounds. Such real time constraints are typically embraced by the concept of quality of service [BBBC98] Quality of Service (QoS) characterizes the non functional properties of a system; it is expressed in terms of a number of quantifiable criteria, e.g. timeliness, capacity, integrity, cost, security, reliability and priority. In this paper we focus on real time QoS parameters, such as ....

....is built will not always yield a reliable measure of QoS capabilities. Information on performance capabilities need to be determined during system development and be used to inform dynamic measurement systems. In response, a number of researchers have considered techniques for the specification [BBBC98,FL98] and verification [BFM98] of Quality of Service. However to date, this work has been restricted to specification and verification using deterministic timing , e.g. putting fixed upper and lower bounds on the time that actions are offered to the environment. This is a useful first step, but ....

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G.S. Blair, L. Blair, H. Bowman, and A. Chetwynd. Formal Specification of Distributed Multimedia Systems. University College London Press, 1998.

.... spectrum of techniques can be classified into various categories such as specification logics, process algebraic techniques, automata based techniques, Petri nets, synchronous languages, and more software engineering oriented languages (such as Z) A survey covering such categories can be found in [Blair98a]. In general, extensions to these languages are regularly being developed. Typically, such extensions address a shortcoming of many specification techniques: whilst they are very good at capturing the functional (qualitative) behaviour of a system, few have the ability to specify the more ....

....different aspects. Our work has focused on a process algebra (LOTOS) for an abstract specification of functional behaviour and has evaluated temporal logic and automata (and real time and probabilistic extensions to each) for the specification of quantitative aspects (see, for example, Lakas96a] [Blair98a] and [Blair98b] Other work elsewhere (e.g. Zave93] Zave96] has considered the use of Z along with automata, Petri nets and formal grammars. 2.3. Aspect weaving In aspect oriented programming, it is the aspect weaver s job to combine the behaviour of the component program (equivalent to our ....

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G.S. Blair, L. Blair, H. Bowman, A. G. Chetwynd, "Formal Specification of Distributed Multimedia Systems", London: UCL Press, 1998.

....timed state sequences are used as a model over which temporal logic formulae are interpreted. These sequences provide the link between the LOTOS specification of abstract behaviour and the LOTOS events referred to in the logic formulae. A full justification for our choice of logic can be found in [Blair95b, Blair97]. It should be noted that, in addition to using QTL to specify requirements, we also use QTL to specify real time assumptions. The use of the logic for both requirements and assumptions simplifies the verification process [Blair95b] 4. A COMPARATIVE EXAMPLE 4.1. The Lip Synchronisation Problem ....

....between the sound and video presentations are presented below. Note that in this example, no jitter is permitted on the sound presentation. Therefore, it is only the jitter on the video data which can cause the presentation to drift out of 3 This example is taken from a book by the authors [Blair97] and is reproduced with the kind permission of UCL Press. 6 synchronisation (for example, if video frames repeatedly arrive late) 3. Synchronisation of Sound and Video (i) The video presentation must not lag the associated sound presentation by more than 150ms. ii) The video presentation ....

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Blair, G.S., Blair, L., Bowman, H., and Chetwynd, A., "Formal Specification of Distributed Multimedia Systems", UCL Press, In Press, 1997.

....This prevents the costly scenario of constructing a finished system only to find that it doesn t meet its realtime requirements. Formal specification and verification offers great potential in this respect. Consequently, a number of researchers have considered techniques for the specification [3, 10, 17, 9] and verification [5] of multimedia systems. One contribution of this body of work is to identify a number of canonical examples of multimedia systems, e.g. a multimedia stream and a lip synchronisation algorithm [3] The latter is particularly important as it offers a non trivial example of ....

....number of researchers have considered techniques for the specification [3, 10, 17, 9] and verification [5] of multimedia systems. One contribution of this body of work is to identify a number of canonical examples of multimedia systems, e.g. a multimedia stream and a lip synchronisation algorithm [3]. The latter is particularly important as it offers a non trivial example of real time synchronisation between continuous media. The lip sync example was first described in the synchronous language Esterel [18] Then specifications in a number of different formalisms were presented, e.g. in a ....

[Article contains additional citation context not shown here]

G.S. Blair, L. Blair, H. Bowman, and A. Chetwynd. Formal Specification of Distributed Multimedia Systems. University College London Press, September 1997.

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Blair,G.S., Blair,L., Bowman,H., Chetwynd,A.: Formal Specification in Distributed Multimedia Systems. University College London Press (1997).

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G. Blair, L. Blair, H. Bowman, and A. Chetwynd. Formal Specifications of Distributed Multimedia Systems. UCL Press, 1988.

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