Haridi, S. and Brand, P. (1988). Andorra Prolog: an integration of Prolog and committed choice languages. In Proc. of the International Conference on Fifth Generation Computer Systems, pages 745--754, Tokyo. Institute for New Generation Computer Technology (ICOT).  Home/Search   Document Not in Database   Summary   Related Articles   Check

....execution. The other direction aims at the parallel execution of pure logic or Prolog programs that involve searching. Programmers may specify control only for guiding execution. OR parallelism was exploited first [2] 26] 8] 43] and AND parallelism has been incorporated also [9] 16] 45][15]. There has been a long history of controversy between the proponents of these two directions. Proponents of concurrent logic programming languages claim that pure logic programs are not expressive enough to describe e#cient parallel algorithms or to make e#ective use of the computational power ....

....an ordinary logic language and the other using a concurrent logic language, have been compared from the semantics and performance points of view. There are several proposals for unifying these two families of languages; Clark and Gregory [6] propose a hybrid language approach and Haridi and Brand [15] propose a unified language called Andorra. However, we believe that the combination of these languages should be made very carefully and only when a well defined and semantically clear interface can be defined between them. The viewpoints discussed in Section 2.4 will help graceful combination. ....

Haridi, S. and Brand, P. Andorra Prolog: An Integration of Prolog and Committed Choice Languages. In Proc. Int. Conf. on FGCS'88, ICOT, 1988, pp. 745--754.

....by evaluating multiple AND branches of the search space concurrently; and those that seek to exploit both. There are a considerable number of systems that use one or more of these strategies including MUSE [3] OR parallel) PNU Prolog [71] and Prolog [47] AND parallel) and Andorra [42] (both) All these systems try to execute unmodified Prolog programs in parallel, and assume by default that any two conjuncts or disjuncts may be executed in parallel. This can lead to what is sometimes called embarrassing parallelism where very many small parallel tasks are created such that the ....

S. Haridi and P. Brand. Andorra Prolog: An integration of Prolog and committed choice languages. In Proceedings of the International Conference on Fifth Generation Computer Systems, pages 745--754, Tokyo, Japan, 1988.

....if the second literal is proved before the first one. Hence a logic language with an operational semantics that prefers the evaluation of deterministic literals (i.e. literals having at most one matching clause) would avoid the infinite loop in the last example. The Andorra computation model [62] or Prolog with Simplification [42] have this property. Therefore the flattening technique yields better results if the target of the transformation is a logic programming system with an extended computation model. If an efficient implementation of such an extended computation model is not ....

....normalization would correspond to the deletion of literals in the flattened program. 2. Normalization evaluates terms even if more than one rule is applicable. For instance, the term 0 0 is normalized to 0 w.r.t. the multiplication rules of Example 2. 5 which are not deterministic in the sense of [42, 62]. Example 3.3. Consider the following program for computing the maximum of two natural numbers: 30 max(X,Y) Y : le(X,Y) max(X,Y) X : le(Y,X) le(0,N) le(s(M) s(N) le(M,N) If we compute the maximum of two identical numbers, e.g. we want to solve the equation ....

S. Haridi and P. Brand. Andorra Prolog: An Integration of Prolog and Committed Choice Languages. In Proc. Int. Conf. on Fifth Generation Computer Systems, pp. 745--754, 1988.

....at Bristol university. The IDIOM model [37] is a proposal for exploiting the three forms of parallelism: independent ANDparallelism, stream AND parallelism, and OR parallelism. Andorra I and IDIOM are based on the Andorra computational model originally proposed by David H. Warren and discussed in [42]. To our knowledge, there are only two OR parallel Prolog systems that support the full Prolog language. The first one is Aurora [65] which has been developed as a collaborative effort between groups at Argonne National Laboratory, the University of Bristol, and SICS. The other one is Muse, ....

....[4, 14, 23, 28, 47, 54, 79, 92] incorporating different binding schemes. Binding schemes for combining OR parallelism with AND parallelism have also been developed [19, 30, 56, 94] Recent approaches attempt to exploit stream AND parallelism while retaining the full search capability of Prolog [42, 43, 71, 80, 76]. Other important issues in the efficient implementation of OR parallel Prolog are scheduling work so as to minimize speculative computations, and supporting the Prolog side effects and cut [3, 46, 45, 55] 3.1.1 History of the BC Machine Research In 1986, a research project at SICS, called the ....

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Seif Haridi and Per Brand. Andorra Prolog---an integration of Prolog and committed choice languages. In International Conference on Fifth Generation Computer Systems 1988. ICOT, 1988.

....logic languages improve logic languages by avoiding impure control features. Hence, functions are a declarative notion to improve control in logic programming. Moreover, they provide for useful functional programming techniques and lead to clearer programs. 1 The Andorra computation model [18] prefers the evaluation of literals where at most one clause is applicable. In case of clauses with overlapping left hand sides, there may be several clauses applicable leading to the same result. The possible pruning of the computation space in these cases is not covered by the Andorra model. ....

S. Haridi and P. Brand. Andorra prolog: An integration of prolog and committed choice languages. In Proc. Int. Conf. on Fifth Generation Computer Systems, pages 745--754, 1988.

....operations on constraints. Again not sufficiently instantiated constraints lead to delays on the outcome of these operations and sometimes lead to incomplete operational semantics. Based on this principle, some well known systems have been developed: CLP(R) 18] CHIP [10, 11] PrologIII [5] AKL [15]. An early approach towards CLP has been presented in [32] where a sequential method was utilized. In both LP and Constraint Logic Programming (CLP) control conditions and operations are sensitive to the availability of certain information. In order to become applicable, a rule must assure that ....

S. Haridi and P. Brand. ANDORRA prolog: An integration of prolog and committed choice languages. In Proc. of the International Conference on Fifth Generation Computer Systems FGCS-88, pages 745 -- 754, Tokyo, Japan, November 1988.

....(g i ( T ) can be successfully reduced, then the goal atom can potentially producers if it were not constrained. 12 It should be noted that an alternate method than guarded Horn clauses and a variant form of unification has been proposed by D.H.D. Warren in the form of the Andorra principle [20]. The principle is to select deterministic atoms for reduction first (a deterministic goal atom is one that can unify with only a single program clause) Only if there are no deterministic goal atoms available will an atom non deterministically reduce. 13 If it were simple logical implication, ....

Seif Haridi and Per Brand. Andorra prolog: An integration of prolog and committed choice languages. In ICOT [28], pages 745--754.

....user defined predicates. Parallelizers On multi processor machines it is of course desirable to keep all processors occupied. Logic programs typically have fewer side effects than their imperative counterparts, and may therefore have more opportunities for parallelization [Tic91, PN91, CWY91, HB88] Abstract Interpretation Many analysis methods can be captured in the framework of abstract interpretation [CC92, CC77, Jan90, BJCD87, Bru91, Mel87, MS88] In essence, a property of a program can sometimes be deduced by running an abstract form of the program, where operations and data ....

....the methods outlined in this chapter can therefore improve the precision of their algorithm. 5. In a parallel execution strategy with or parallelism, a set of processors working on mutually exclusive rules can be relieved of their duties as soon as one of them succeeds. Also, in the Andorra model [HB88] goals with only one matching clause are executed before other goals. Static analysis has been used to detect such properties of goals [CWY91, PN91] After discussing related work and establishing some required terminology, we illustrate the ideas of our technique by means of a small example ....

S. Haridi and P. Brand. Andorra Prolog -- An integration of Prolog and Committed Choice Languages. In Proceedings of the 1988 International Conference on Fifth Generation Computer Systems, Tokyo, Japan, pages 745--754, 1988.

....kinds of systems handling capability required by concurrent knowledge based systems like fair scheduling of sub tasks within the whole computation. The same applies to other attempts to reconcile stream and parallelism with don t know nondeterminism like the lazy non determinism of Andorra Prolog [9] and Pandora [2] and P Prolog s use of the exclusive relation [19] Thus while Prolog like languages can program the knowledge base querying aspects of concurrent knowledge based systems by exploiting don t know non determinism, and while the CLP languages can sustain systems programming ....

S. Haridi and P. Brand, "Andorra Prolog: an integration of Prolog and committed choice languages," in Proceedings of the International FGCS Conference, Tokyo, (December 1988).

....Process Model [78] is also similar to Conery s model, but also can exploit dependent and parallelism through the Data Join Graphs (DJP) that allows to represent dependencies between goals, contrarily to the literal ordering graph used by Conery s model, and DeGroot s CGEs. The Basic Andorra Model [139, 65] combines dependent and parallelism in the style of committed concurrent systems, w ith only determinate goals being allowed to be executed in parallel, w ith or parallelism in the style of Aurora. An implementation of the Basic Andorra Model, Andorra I [102, 148] is the main subject of discussion ....

Seif Haridi and Per Brand. Andorra Prolog -- an integration of Prolog and committed choice languages. In Proceedings of the 1988 International Conference on Fifth Generation Computer Systems. ICOT, 1988.

....by the methods outlined in this paper can therefore improve the precision of their algorithm. 5. In a parallel execution strategy with or parallelism, a set of processors working on mutually exclusive rules can be relieved of their duties as soon as one of them succeeds. Also, in the Andorra model [HB88], goals with only one matching clause are executed before other goals. Static analysis has been used to detect such properties of goals [CWY91, PN91] After discussing related work and establishing some required terminology, we illustrate the ideas of our technique by means of a small example ....

Seif Haridi and Per Brand. Andorra Prolog -- An integration of Prolog and Committed Choice Languages. In Proceedings of the 1988 International Conference on Fifth Generation Computer Systems, Tokyo, Japan, pages 745--754, 1988.

....by pruning alternative paths in the search tree, it is possible to remove choice points, thereby making the program more deterministic. Because of the drive for exploiting parallelism, however, many recent innovative logic programming schemes such as NU Prolog [48] Reform Prolog [4] Andorra [25], and Godel [27] have been devised with a more flexible control procedures but allowing for explicit control directives by the programmer. Moreover, new pruning operators such as the one solution in NU Prolog, the commit in Andorra, and the Godel commit , that do not depend, like the traditional ....

....is called a choice point . In making a general study of determinacy it is important to try to separate control issues from the definitions since in some computational models the selection rule is defined in terms of the possible deterministic behaviour of the program. For example, in Andorra [25], determinate atoms are selected in preference to non determinate ones. On the other hand, the control still needs to be considered since the order in which literals are selected can affect the determinacy. There are a number of ways in which the intended selection rules can be specified. In ....

S. Haridi and P. Brand. Andorra Prolog: An integration of Prolog and committed choice languages. In Proceedings of the International Conference on Fifth Generation Computer Systems, Tokyo, pages 745--754, 1988.

....determinacy preprocessor has been implemented in Prolog[13] It accepts standard Prolog programs and in addition the extensions described in Section 3. In the future, we may extend it to generate the determinacy code for other languages of the Andorra family such as Pandora[2] and Andorra Prolog[7]. 5 Results In this section, we present initial performance data for Andorra I. All timings were made on a Sequent Symmetry. Each Andorra I worker was supported by a separate processor. 5.1 Engine Speed Table 1 compares a sequential version of Andorra I with C Prolog to show the basic speed of ....

Seif Haridi and Per Brand. Andorra Prolog--an integration of Prolog and committed choice languages. In International Conference on Fifth Generation Computer Systems 1988, ICOT, 1988.

....of a dis statement has both a guard and a body. The guards are used immediately to check failure. If a guard G i fails then its alternative is eliminated. This extension is sometimes called determinacy directed execution. It was discovered by D.H.D. Warren and called the Andorra principle [42, 85]. The dis statement can be programmed with the space operations as follows. First encapsulate each guard of the dis statement in a separate space. Then execute each guard until it is stable. Discard all failed guards. Finally, using the Choose operation, create a choice point for the remaining ....

Seif Haridi and Per Brand. Andorra Prolog -- an integration of Prolog and committedchoice languages. In Institute of New Generation Computer Technology (ICOT), editor, Proceedings of the International Conference on Fifth Generation Computer Systems (FGCS), volume 2, pages 745--754, Tokyo, Japan, November 1988. Ohmsha Ltd. and Springer Verlag.

....The idea has been conceived in the context of Prolog, where the disjunctive combinators are Horn clauses, and are, in Prolog, only reduced by search. The above described principle has been first discovered by D. H. D. Warren and has been called Basic Andorra Principle by Haridi and Brand in 1988 [44]. It has been independently discovered by Smolka in 1991, who referred to it as residuation [135] Residuation occured first in the work of At Kaci and Nasr [6] even though there has been no explicit link to search. Similar ideas have already been explored in MU Prolog by Naish [98] The ....

Seif Haridi and Per Brand. ANDORRA Prolog - an integration of Prolog and committed choice languages. In Institute for New Generation Computer Technology (ICOT), editor, Proceedings of the International Conference on Fifth Generation Computer Systems, volume 2, pages 745--754, Berlin, Germany, November 1988. Springer-Verlag.

....then that remaining branch is taken. If more than one branch remains, then 3 a choice point is created. The dis statement extends Prolog style execution to interleave deterministic and non deterministic reduction. This extension was discovered by D.H.D. Warren and called the Andorra principle [23, 57]. The dis statement is a powerful way to do Prolog style generative execution. However, the dis statement does not scale up to class II problems. In our opinion, its only values are pedagogical and exploratory. That is, it can be used on small examples to explore and understand a search space, ....

Seif Haridi and Per Brand. Andorra Prolog -- an integration of Prolog and committedchoice languages. In Institute of New Generation Computer Technology (ICOT), editor, the International Conference on Fifth Generation Computer Systems (FGCS), volume 2, pages 745--754, November 1988.

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Haridi, S. and Brand, P. (1988). Andorra Prolog: an integration of Prolog and committed choice languages. In Proc. of the International Conference on Fifth Generation Computer Systems, pages 745--754, Tokyo. Institute for New Generation Computer Technology (ICOT).

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Haridi, S. and Brand, P. (1988). Andorra Prolog: an integration of Prolog and committed choice languages. In Proc. of the International Conference on Fifth Generation Computer Systems, pages 745--754, Tokyo. Institute for New Generation Computer Technology (ICOT).

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