Focus points and convergent process operators

We present a strategy for finding algebraic correctness proofs for communication systems. It is described in the setting of $mu$CRL (Groote and Ponse 93) which is, roughly, ACP (Baeten and Weijland 90, Bergstra and Klop 84) extended with a formal treatment of the interaction between data and processes. The strategy has already been applied successfully in non-trivial case studies (e.g., Bezem and Groote 94, and Fredlund, Groote, and Korver 95), but was not explicitly identified as such. Moreover, the protocols that were verified in these papers were rather complex, so that the general picture was obscured by the amount of details. In this paper, the proof strategy is materialised in the form of definitions and theorems. These results reduce a large part of protocol verification to a number of trivial facts concerning data parameters occurring in implementation and specification. This greatly simplifies protocol verifications and makes our approach amenable to mechanical assistance; experiments in this direction seem promising. The strategy is illustrated by several small examples and one larger example, the Concurrent Alternating Bit Protocol (CABP). Although simple, this protocol contains a large amount of internal parallelism, so that all relevant issues make their appearance

A two-level approach to automated conformance testing of VHDL designs

For manufacturers of consumer electronics, conformance testing of embedded software is a vital issue. To improve performance, parts of this software are implemented in hardware, often designed in the Hardware Description Language VHDL. Conformance testing is a time consuming and error-prone process. Thus automating (parts of) this process is essential. There are many tools for test generation and for VHDL simulation. However, most test generation tools operate on a high level of abstraction and applying the generated tests to a VHDL design is a complicated task. For each specific case one can build a layer of dedicated circuitry and/or software that performs this task. It appears that the ad-hoc nature of this layer forms the bottleneck of the testing process. We propose a {em generic solution for bridging this gap: a generic layer of software dedicated to interface with VHDL implementations. It consists of a number of Von Neumann-like components that can be instantiated for each specific VHDL design. This paper reports on the construction of and some initial experiences with a concrete tool environment based on these principles

Focus points and convergent process operators

We present a strategy for finding algebraic correctness proofs for communication systems. It is described in the setting of $mu$CRL (Groote and Ponse 93) which is, roughly, ACP (Baeten and Weijland 90, Bergstra and Klop 84) extended with a formal treatment of the interaction between data and processes. The strategy has already been applied successfully in non-trivial case studies (e.g., Bezem and Groote 94, and Fredlund, Groote, and Korver 95), but was not explicitly identified as such. Moreover, the protocols that were verified in these papers were rather complex, so that the general picture was obscured by the amount of details. In this paper, the proof strategy is materialised in the form of definitions and theorems. These results reduce a large part of protocol verification to a number of trivial facts concerning data parameters occurring in implementation and specification. This greatly simplifies protocol verifications and makes our approach amenable to mechanical assistance; experiments in this direction seem promising. The strategy is illustrated by several small examples and one larger example, the Concurrent Alternating Bit Protocol (CABP). Although simple, this protocol contains a large amount of internal parallelism, so that all relevant issues make their appearance

Focus points and convergent process operators: a proof strategy for protocol verification

AbstractWe present a method for efficiently providing algebraic correctness proofs for communication systems. It is described in the setting of μCRL [J.F. Groote, A. Ponse, The syntax and semantics of μCRL, in: A. Ponse, C. Verhoef, S.F.M. van Vlijmen (Eds.), Algebra of Communicating Processes, Workshops in Computing, Springer, Berlin, 1994, pp. 26–62] which is, roughly, ACP [J.C.M. Baeten, W.P. Weijland, Process Algebra, Cambridge Tracts in Theoretical Computer Science, vol. 18, Cambridge University Press, Cambridge 1990, J.A. Bergstra, J.W. Klop, The algebra of recursively defined processes and the algebra of regular processes, in: Proceedings of the 11th ICALP, Antwerp, Lecture Notes in Computer Science, vol. 172, Springer, Berlin, 1984, pp. 82–95] extended with a formal treatment of the interaction between data and processes. The method incorporates assertional methods, such as invariants and simulations, in an algebraic framework, and centers around the idea that the state spaces of distributed systems are structured as a number of cones with focus points. As a result, it reduces a large part of algebraic protocol verification to the checking of a number of elementary facts concerning data parameters occurring in implementation and specification. The resulting method has been applied to various non-trivial case studies of which a number have been verified mechanically with the theorem checker PVS. In this paper the strategy is illustrated by several small examples and one larger example, the Concurrent Alternating Bit Protocol (CABP)

A computer checked algebraic verification of a distributed summation algorithm

We present an algebraic verification of Segall’s propagation of information with feedback algorithm and we report on the verification of the proof using the PVS system. This algorithm serves as a nice benchmark for verification exercises (see [2, 8, 17]). The verification is based on the methodology presented in [7] and demonstrates its suitability to deliver mechanically verifiable correctness proofs of highly nondeterministic distributed algorithms

A computer checked algebraic verification of a distributed summation algorithm

We present an algebraic verification of Segall’s propagation of information with feedback algorithm and we report on the verification of the proof using the PVS system. This algorithm serves as a nice benchmark for verification exercises (see [2, 8, 17]). The verification is based on the methodology presented in [7] and demonstrates its suitability to deliver mechanically verifiable correctness proofs of highly nondeterministic distributed algorithms

The birth of the mandate idea and its fulfilment in Iraq up to 1926

This thesis traces the mandate concept as embodied in Art. 22 of the Covenant of the League of Nations as an intrinsic feature of the British Imperial mind. Therefore the purview of our study is British imperial thinking and policy making during and after the First World War. It was in respect to Iraq that the mandate concept, as a distinct policy, was formulated for the first time by Mark Sykes. The mandate concept sprang from that part of British Imperial thought which was deeply affected by official apprehension about the Empire's position in the Middle East. This thesis is proved in the following exegesis of the analytical framework of our thesis. Chapter I describes contemporary reactions and thinking on new models of peace order. We have concentrated mainly on Arnold Toynbee's and Leonard Woolf's thinking. Both crystallize the contemporary argumentation in an important way. While they are placed under the sub-title, Premises of Scientific Peace, others such as Amery are for their imperial senti- ments discussed under the second sub-title: Imperial Sentiment and its Impact on Planning for a New World Order. The two chapters reveal the inner conditions which allowed the birth of the mandate compromise. Many of the ingredients of the mandate concept stemmed from the doctrines of democracy. How-ever when these penetrated the East the Arab response to them was bound to bring about conflict with British imperial interests. Yet in its turn, the Empire's reaction and policy was not of one kind. It was marked with the three-cornered antagonism between the Government of India, the Arab Bureau at Cairo and Whitehall. The pivot of this study of British war-time policy is the chapter called: The British Glimpse of a Middle East Empire. Interestingly, the above antagonism gave rise to ideas of a British Middle Eastern Empire. There course and fate was implicit in the frequent committee chages, departmental struggle against rule by committee and in debates on immediate issues of policy. We regard their fate and their impact on the decision-making structure in Whitehall as more indicative of the state of the British will to rule in the East than such paper-designs as the MacMahon-Hussein correspondence, the Sykes-Picot Agreement or the De Bunsen Committee Report. From this angle our chapter is meant to serve as a corrective to the weight of those paper-designs; further it puts the final creation of the Middle East Department in its right imperial perspective. The sectionhas been provided with what one may call a "trailer". Called, Some Features of the Mesopotamian Campaign, it gives the story of how the Admiralty pushed through its policy of physical control over the oil-bearing regions of Iraq. It was their policy which led to the capture of Mosul. The study of the war-time policy concludes with the section entitled: Mark Sykes and the Origin of the Iraq Mandate. This chapter is meant to be a synopsis of the contrapuntal studies of the Matrix of the Mandate Idea, on the one hand, and, on the other, the British Glimpse of a Middle East Empire. This syno-psis is amply contained in Mark Sykes's hitherto unknown memorandum of January 1918, and in his original way of looking at international affairs. Prompted by this find we have scrutinized Sykes's functioning in the policy making of the Lloyd George Cabinet. His thought and personality are separated out under the three topics of Sykes as (1) the campaigner and partisan official, (2) the admonisher and conscience of the age, (3) the nostalgic and reflective mind. The description of his failure to achieve his policy at the end of the war foreshadows the last chapter of this first part of the thesis. Entitled, The "A" mandate before the Supreme Council, this chapter investigates features which point to conflicting views as to the advisability of rendering the mandate concept more strictly. This chapter puts Art.22 of the Covenant in its right perspective as a tentative and somewhat incomplete compromise principle in the new international law. By its resultant vagueness the concept afforded considerable discretion to imperialist policy. The checks which were supposed to mitigate such a policy are examined in the concluding chapter VIII, entitled: Iraq before the League of Nations. The concept has emerged from the first part of our thesis as Janus-faced, combining an extremely flexible political instrument for the expansion of imperial control with an evolutionary political doctrine of "democratic control". In contrast, internationally, the mandate was regarded by League champoins as a check on the imperialistic ambitions of the mandatory. Of these three aspects the evolutionary principle was the new colonial dress. The studyof the application of the mandate starts with a detailed analysis of: The Political Role of the Oil-bearing Regions of Iraq. The oil-issue is followed as it ran like a red line through Iraq's early political history up to 1926. The first section of the ensuing chapter, Towards the Cairo-Conference, deals with what we call the "import article" of the colonial idea in the Middle East as it was designed and propagated advertisement-like for consumption in Britain by such on the spot experts as Gertrude Bell. The remaining sections deal, again contrapuntally, with public opinion and the taxpayer rationale in Britain and the final synthesis of the Cairo-policy. The chapter on the Cairo-Conference, is the opening movement for the subsequent constitutional development of Iraq, in the course of which Britain , set by set, gears the expansion of the governmental infra-structure to the achievement of her imperialistic aims of control. As in the previous chapter the part entitled, The British Gambits in the Constitutional Development of Iraq, gives much room to the role played by personalities. These, because of their more discernible and distinct capacities and idiosyncracies became what one may call "substitutes" for the far less calculable social forces, economic conditions and political circumstances in turmoil. There follows, in the chapter, The Shaping of Iraqis External Relations, a desciption of some features of Iraqis integration into the contemporary international context. The concluding chapter, euphemistically entitled, Iraq before the League of Nations, endeavours to define the three-cornered relationship between Britain, Iraq and the League within the context of immediate practice rather than of the myth which afterthought has woven around it.</p

On recognizable timed languages

Abstract. In this work we generalize the fundamental notion of recognizability from untimed to timed languages. The essence of our definition is the existence of a right-morphism from the monoid of timed words into a bounded subset of itself. We show that the recognizable languages are exactly those accepted by deterministic timed automata and argue that this is, perhaps, the right class of timed languages, and that the closure of untimed regular languages under projection is a positive accident that cannot be expected to hold beyond the finite-state case.