de Bakker J.W., Comparative Semantics for Flow of Control in Logic Programming without Logic, Information and Computation, Vol. 94, no. 2, 1991, pp. 123-179.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....to occur at the same time. The more complex operational semantics O s and the denotational semantics Den have no counterpart in [Br90] FLP84] and [Mo81] Although they are of classical metric inspiration, these last two semantics still present some originality with related work ( BZ82] [B91], KR90] BKPR89] It arises essentially from the three following points : i) our concern with generalized Horn clauses, which has not been done before and which requires new solutions; in particular, it should be noticed that the form of communication provided by the Pi and ....

....theorem, stating the existence of a unique fixed point of contractions in complete metric spaces. He is referred to [Ll87] and [En89] when need be. Furthermore, lack of space prevents us from describing all the metrics used in this paper. We will however employ the classical ones and refer to [B91] for such a description. 4 Semantic translation As pointed out in Section 1, the operator , acting in goals, can be simulated by the operator Pi acting in clauses. Semantics for the language CSLP can thus be made in two ways. One consists of translating the programs in the sublanguage ....

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de Bakker J.W., Comparative Semantics for Flow of Control in Logic Programming without Logic, Information and Computation, Vol. 94, no. 2, 1991, pp. 123-179.

....theorem, stating the existence of a unique fixed point of contractions in complete metric spaces. He is referred to [17] and [10] when need be. Furthermore, lack of space prevents us from describing all the metrics used in this paper. We will however employ the classical ones and refer to [7] for such a description. As a matter of notation, P nco (E) is subsequently used to denote the set of non empty and compact sets with elements from E. 4 Operational semantics Two first semantics of Log can be expressed operationally by means of a transition system, defined in Plotkin s style ....

J.W. de Bakker. Comparative Semantics for Flow of Control in Logic Programming without Logic. Information and Computation, 94(2):123--179, October 1991.

....automata are deterministic. Generally, this does not hold for deterministic automata. There is yet another characterization of the final automaton L, stemming from [Rut98] varying on a result from [Bre98] which has featured in certain metric models of concurrent programming languages (cf. [dB91] and [BV96] It will play no role in the rest of the paper. Let A # # = A # # A # # A # #, where A # is as before, A # is the set of all infinite words over A, and A # # = w # w # A # , assuming that # ## A) For an infinite word w = a 1 a 2 a 3 in A # and a ....

J.W. de Bakker. Comparative semantics for flow of control in logic programming without logic. Information and Computation, 94(2):123--179, 1991.

....functor D 0 , consists of metrically closed subsets. Such sets have been used at various places in the work of the French and Dutch schools of Nivat and De Bakker on metric semantics (cf. the recent textbook [BV96] The notion of consistent language corresponds to the notion of reduced set in [dB91]. Automata theory has been and still is commonly understood as essentially algebraic. cf. Ginzburg s Algebraic theory of automata [Gin68] Conway s Regular algebra and finite machines [Con71] and Kozen s recent textbook Automata and computability , from which the following quotation is taken ....

J.W. de Bakker. Comparative semantics for flow of control in logic programming without logic. Information and Computation, 94(2):123--179, October 1991.

....BT this paper; LT 4 Inspired by Concurrent Logic Languages we study in this paper the second options for the choice and the atomizer. The paper is organized as follows. First we give a uniform version of the language L. in which we are studying the meaning of the program connectives only (cf. [dB88, dV90]) In order to study the parallel choice connective, we have included an always deadlocking failing action ffi in the language. Both an operational and a denotational semantics for the language are defined. The operational semantics only yields the finite behaviour (that is termination and ....

J.W. de Bakker. Comparative semantics for flow of control in logic programming without logic. Technical Report CS-R8840, CWI, 1988. To appear in Informatition and Computation.

....Logic Languages in the present language in such a way that the operational semantics of programs written in these languages coincides with the induced semantics of the embedded program. We consider a uniform language L for which we study the meaning of the program connectives only (c.f. [dB91, Vaa89]) In order to study the parallel choice connective, we have included an always deadlocking failing action ffi in the language. Both an operational and a denotational semantics for the language are defined, in sections 3 and 5, respectively. The operational semantics only yields the finite ....

J.W. de Bakker. Comparative semantics for flow of control in logic programming without logic. Information and Computation, 94(2):123--179, 1991.

....acceptable implementations of pruning operators. In general, semantical methods, in particular compositional ones, seem somewhat lacking behind in the understanding of concurrency in logic programming together with extra logical control flow operators. Only a few references are known to us, e.g. [2, 8] to mention two of them. Paraphrasing the mantra of logic programming one can argue that concerning the semantical analysis of concurrent logic programming one has to deal with logiccontrol instead of with their sum. In this paper we report on a comparative semantics for the control flow kernel of ....

....the control flow kernel of or parallel logic programming with a commit operator. The comparison is made for a step oriented operational semantics and a continuationstyle denotational one. The restriction to the control flow follows the logic programming without logic approach as advocated in [2]. It turns out that already in this relatively simple case intricate modeling tricks have to be applied, both for a succinct description (encoding of scope information) and for the justification of the denotational semantics (the technical aspect of using finitely non empty and closed sets instead ....

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J.W. de Bakker. Comparative semantics for flow of control in logic programming without logic. Information and Computation, 94:123--179, 1991.

....a semantic variant of the considered program P that allows several independent reductions to occur at the same time. The denotational semantics Den has no counterpart in [3] 10] and [16] Although it is of classical metric inspiration, it still presents some originality with related work ( 6] [5], 14] which arises essentially from the two following points : i) our concern with extended Horn clauses, which has not been done before and which requires new solutions; in particular, it should be noticed that the form of communication provided by the Pi and operators is ....

....Banach s theorem, stating the existence of a unique fixed point of contractions in complete metric spaces. He is referred to [15] and [9] when need be. Furthermore, lack of space prevents us from describing all the metrics used in this paper. We will however employ the classical ones and refer to [5] for such a description. 5 Semantic translation As pointed out in section 1, synchronization can be specified in two places: in goals, by means of the operator , and in clauses, by means of the operator Pi . These two operators thus act in a dual way. It turns out, however, that it is ....

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J.W. de Bakker. Comparative Semantics for Flow of Control in Logic Programming without Logic. Technical Report CS-R8840, Centre for Mathematics and Computer Science (CWI), Amsterdam, The Netherlands, 1988.

....Prolog from the specification of the flow of control, e.g. backtracking, the cut operator) This is achieved by extracting the uniform language B from Prolog uniform in the sense of [BKMOZ] which contains only the latter issues. Fitting within the Logic Programming without Logic approach, [Ba2]) our denotational model developed for the abstract backtracking language has enough flexibility for further elaboration to a nonuniform denotational model of Prolog itself. Moreover, the equivalence of this denotational semantics and an operational semantics for Prolog is a straightforward ....

....paradigm ( Kw] at the meta level. In fact, several semantics of logic programming languages can be considered as generalizations of established models for imperative languages with respect to the control; the extensions made are concerned with the particular logic component. cf. GCLS] Kk] [Ba2]a. See in particular [BK] for a related approach in the setting of Concurrent Prolog. Unfortunately there is a price to pay for our two pass approach, albeit just a syntactical one. Since we restrict procedure names in B to have just one procedure body, we can consider clauses with pairwise ....

J.W. de Bakker, "Comparative Semantics for Flow of Control in Logic Programming without Logic," Report CS-R8840, Centrum voor Wiskunde en Informatica, Amsterdam (1988). To appear in Information and Computation.

....of this paper is [KR]a where for the first time the observation was made that compact equivalence proofs could be realized using higher order transformations. To a great extent, we also benefit from the work on metric semantics of concurrency performed by De Bakker e.a. e.g. BZ] BKMOZ] BM]a, [Ba2]. It is a pleasure to thank the forum formed by the members of the working group on concurrency, Jaco de Bakker, Frank de Boer, Joost Kok, Jan Rutten and others for their comments and the good scientific atmosphere they provided. We are also indebted to Philippe Darondeau for his suggestions ....

....Semantics and Denotational Semantics for B In this section we introduce the abstract backtracking language B. This uniform language was studied also in [BV]a for it captures the control flow of Prolog with cut, the latter being the main interest of the particular paper. See also [BaKo] Vi]a, [Ba2]a for similar uses of intermediate abstracta in deriving sound denotational semantics for logic programming languages. In the present paper however, we will focus on the residue B itself to serve as a case study for our method of comparing operational and denotational semantics. 4.1) DEFINITION ....

J.W. de Bakker, "Comparative Semantics for Flow of Control in Logic Programming without Logic," Report CS-R8840, Centrum voor Wiskunde en Informatica, Amsterdam (1988). To appear in Information and Computation.

....induced by the type of transition system specifications. In the present paper we propose yet another format for transition system specifications which is suitably expressive to describe continuation style transition systems, as has been frequently used in comparative (metric) semantics, [AB88, AR89, Rut90b, BV91b, BV89, Bak91, EV93, BV92b]. The transition system specifications of these papers do not fit in the formats mentioned above, but will fit into the format introduced by the present paper, that we will call the stalk format. One can view it as a many sorted extension of the single sorted tyftformat without lookahead, but ....

....E, representing termination, there is no rule or axiom. Example 3.8 The next transition system specification exemplifying the stalk format, is a specification for ( Sigma cut ; cut ) The system is used, in the literature, for an operational model for the flow of control of Prolog with cut. See [Bak91, Vin90, BV89]. The various classes of terms playing a role, can (as alternative to the description of Example 3.2) be summarized by the BNF s (2 S) ff j j fail j s ; s j s s j r (2 R) E j u : r t (2 T ) Delta j r t u (2 U) s t with ff a meta variable ranging over A, a ....

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J.W. de Bakker. Comparative semantics for flow of control in logic programming without logic. Information and Computation, 91:123--179, 1991.

....the implementation of a distributed medical expert system is described, illustrating the distribution of control over multiple active objects using DLP. Semantics In this paper we will focus mainly on the behavioral aspects of DLP. Following the logic programming without logic approach (cf. [de Bakker, 1991]) we will propose an abstract, uninterpreted language B that will serve as a vehicle for an examination of the asynchronous rendez vous as present in DLP. The strategy of analyzing the control flow of a skeletal language first, before given an account of the full programming language under ....

.... under consideration has been shown profitable in, e.g. Kok, 1988] and [de Bruin and de Vink, 1989] Since the semantics for (the core of) Prolog including the cut operator, and therefore of individual DLP objects, has been extensively studied in [Jones and Mycroft, 1984] de Vink, 1990] and [de Bakker, 1991], attention is given primarily to the creation of processes and the flow of control during communication. Complementary to the approach followed here one could stress the logical aspects of DLP by studying a declarative semantics as done, e.g. for contextual logic programming in [Monteiro and ....

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J.W. de Bakker, Comparative semantics for flow of control in logic programming without logic, Information and Computation 91 (1991) pp. 123-179

....and operational semantics of logic programs, the second to deal also with some metalogical, built in relations. Our contribution is related to those approaches which employ mathematical concepts and techniques traditionally applied in the imperative setting. In particular, in [dV90] dBK90] and [dB91] the semantics of various logic programming languages is investigated by distinguishing between the logic and the control part of a program. Since their aim is to compare logic programming languages with various control features, they focus on the study of the control part, by abstracting ....

J.W. de Bakker. Comparative semantics for flow of control in Logic Programming. Information and Computation, 94:2:123--179, 1991.

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