P.M. Hill and J.W. Lloyd. The GSdel report. Technical report, Department of Computer Sci- ence, University of Bristol, Bristol, 1991.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....module mapping parse trees to DPL representations, a representation processor which determines truth conditions, falsity conditions and presupposition failure conditions, and an evaluator of these conditions in a database model. The implementation uses the logic pro gramming language GSdel [6], an exper imental successor of Prolog, with similar functionality and expressiveness, but with an improved declarative semantics. 1 The Idea of Dynamic Interpretation Recent developments in Natural Language semantics have witnessed a shift away from static representation languages towards ....

P.M. Hill and J.W. Lloyd. The GSdel report. Technical report, Department of Computer Sci- ence, University of Bristol, Bristol, 1991.

.... and Prolog [71] which is a logic programming language based upon higher order logic [72] While early logic programming languages were untyped, type systems have been designed into some modern logic programming languages such as Prolog (whose type system is described in [73] and G odel [35] (a logic programming language based on many sorted logic) 1.2.2 Type systems A variable in a program can take a range of di erent values in a program. A type of a variable places bounds on these values. For example a variable with type bool might only be allowed to take the values true and ....

....Several explicitly typed semantics for logic programming have been presented [30, 34, 50] The semantics of Lakshman and Reddy [50] was also used to prove soundness of the Mycroft O Keefe type system. Several type systems have been de ned for higher order programming with parametric polymorphism [9, 10, 28, 35, 73]. Extending parametric polymorphism with subtyping in the context of logic programming was considered in [23, 65, 89, 94, 95, 110] Soft type systems for logic programming have been investigated in [15] Recent work on types for logic programming have concentrated on implementation techniques for ....

Pat M. Hill and John W. Lloyd. The Godel report. Technical Report 91-02, Department of Computer Science, University of Bristol, Bristol, England, 1991.

....Benchmark (the Modified Andrew Benchmark or MAB) which suits simultaneous testing in varied operating system environments. The major change is that, instead of compiling and linking code for the host machine, a C compiler is included that compiles for an experimental target machine called SPUR [41]. As a result, the same compiler is used on every machine tested. MAB has been used in the research of Macklem [56] and Ousterhout [71] Endo et al. 34] note the problems of benchmarks, particularly in reference to file system testing. In Endo et al. problems of benchmarks are noted, including ....

Hill M. D. et al. SPUR: A VLSI Multiprocessor. Tech. Rep. UCB-CSD-86273, Department of Computer Science, University of California, Berkeley, April 1986.

....that p Psi under 2 or 3 valued completion semantics. SLDNFA on the other hand investigates the computation tree branch per branch and, using an iterative deepening regime or loop detection, will find the abductive answer r. Another procedure, related to abductive reasoning, is presented in [28]. This paper proposes a belief revision procedure to insert (or delete) a formula F in a given logic program P ; more precisely, it computes an update of P such that F can be proven (or no longer can be proven) from it. To insert F , the procedure tries to construct an SLDNF refutation for the ....

....for F following a similar strategy. A problem with this procedure is that, when solutions are generated, program clauses may be deleted which are needed elsewhere to satisfy positive goals, or that atoms are inserted which make negative goals to succeed. This problem is partially solved in [28] by checking afterwards whether the formula to be deleted or to be inserted has a finitely failed SLDNF tree, respectively an SLDNF refutation with respect to the updated program. This assures correctness, but many solutions cannot be found. For example, consider the logic program P 12 : p ....

[Article contains additional citation context not shown here]

A. Guessoum and J.W. Lloyd. Updating knowledge bases ii. Technical Report TR-90-13, Department of Computer Science, University of Bristol, 1990.

....Moreover, the replication of the display for every clause head means that the user inevitably runs out of available screen space on large programs. We deal with this horizon effect in section 2.1. There has been other work on more declarative approaches to debugging Prolog (e.g. Shapiro, 1982; Lloyd, 1986; Pereira, 1986; Pereira and Calejo, 1988) This work has been based on the declarative reading of Prolog, and not on procedural tracing as such. For this reason the work is not reviewed in detail here. For further information on combining the two debugging styles see (Ducasse, 1988; Brayshaw, ....

....searching of the trace as a means of guiding the user to the bug. Their rationale is twofold: firstly they provide automated assistance for bug location for any user, while secondly they permit, for those who so wish, the use of a more declarative method of bug location (after Shapiro, 1982; Lloyd, 1986; Pereira, 1986) The purely declarative logical meaning of a program is meant to be 21 7 94 8:44 am Brayshaw Eisenstadt: Graphical Prolog Tracer, p. 16 insensitive to the ordering of the clauses. In reality (for better or for worse) clause ordering does affect the actual behaviour of a ....

Lloyd, J.W. Declarative Error Diagnosis. Technical Report 86/3, Department of Computer Science, The University of Melbourne, 1986.

....in the program and the query in the form of a finite type graph. Our type system is very similar to the Mycroft O Keefe type system [5] which has its roots in the type systems of functional languages such as ML [4] and which has been adopted for new logic programming languages such as Godel [2]. The main differences are that for simplicity of presentation, in this paper we assume that each function symbol has one signature, and that all types appearing in the program are monomorphic, i.e. we do not deal with polymorphic types. Since both differences make type checking easier, we omit a ....

P. M. Hill and J. W. Lloyd. The Godel report. Technical Report 91-02, Department of Computer Science, University of Bristol, England, 1991.

....predicate logic and thus share its purely declarative semantics. Pure logic programs are not meant to be directly executed, yet their syntax is sufficiently restricted that they are straightforward to translate into executable programs in logic programming languages, e.g. Prolog or Godel [Hill Lloyd 91] We are thus not restricted to any particular logic programming language. For the purpose of this paper, pure logic programs are collections of sentences of the form 8x 1 : t 1 ; xn : t n : pred(x 1 ; xn ) body where pred is a predicate symbol, the x i are distinct variables ....

P. Hill and J. Lloyd. The Godel Report. Technical Report TR-91-02, Department of Computer Science, University of Bristol, March 1991. Revised in September 1991.

....the truthvalue in P ) is then added to E and the process of inducing P 0 from E, and generating examples is repeated until P is equivalent to P 0 . The example set E is then the required test set. 11.2.4. Knowledge base updating Roughly speaking, the problem of knowledgebase updating (see [29, 19, 44, 45, 138, 96, 52]) can be specified as follows. Given is a deductive database D, satisfying a set of integrity constraints I and a formula f not explained by the database. The aim is then to find an updated database which explains the formula f such that all integrity constraints remain satisfied. To illustrate ....

A. Guessoum and J.W. Lloyd. Updating knowledge bases ii. Technical Report TR-90-03, University of Bristol, Department of Computer Science, 1990.

....property (i.e. X withY )withZ = X withZ)withY ) and a Right absorption property (i.e. X with Y ) with Y = X with Y ) Representation ii is quite usual when dealing with sets in logic programming. It is used for instance in [14] in [4] where with is called scons) and also in the Godel language [12]. 15] uses the [ operator but actually its behaviour is that of the with operator of approach ii. Representation ii is also adopted, for instance, in [20] Representation i, on the contrary, is often used when dealing with the problem of set unification on its own, e.g. 6] and [18] where set ....

P.M.Hill and J.W.Lloyd. The Godel Programming Language. Technical Report, CSTR-92-27, University of Bristol, Department of Computer Science, 1992.

....that type classes integrate very nicely with Mercury s mode, uniqueness and determinism systems, and describe how our implementation works. 1 Introduction Traditionally, logic programming languages such as Prolog have had weak, runtime typing. More recent logic programming languages such as Godel[4] and Mercury[12] have embraced strong typing to increase the level of static checking that may be done and thus make their programs more reliable. Their type systems are based on the Mycroft O Keefe adaption [10] of the Hindley Milner type system commonly used in functional languages. These type ....

Pat M. Hill and John W. Lloyd. The Godel report. Technical Report 91-02, Department of Computer Science, University of Bristol, Bristol, England, 1991.

....efforts, however, have been devoted to the design of an effective logic programming language equipped with meta programming capabilities similar to those usually available in Prolog but defined in a cleaner way. Among them, we must mention MetaProlog [2, 4] and, more recently, the G del language [6]. This paper moves along these lines and leads to the definition of an extended logic programming language called LOG which provides meta programming facilities similar to (or, possibly, better than) those of Prolog. It has the very same aims as G del, at least as far as the introduction of ....

....possibly, better than) those of Prolog. It has the very same aims as G del, at least as far as the introduction of meta programming facilities is concerned: to have functionality and expressiveness similar to Prolog, but to have greatly improved declarative semantics compared with Prolog [6]. LOG is also similar in aims to Barklund s proposal [1] defining a naming of Prolog formulas and terms as Prolog terms to create a practical and logically appealing language for reasoning about terms, programs, Also the applications we have in mind are mostly the same as those of the ....

P.M. Hill, J.W. Lloyd: The Gödel Report (Preliminary Version). Technical Report TR-91-02, Department of Computer Science, University of Bristol, March 1991.

....logic descriptions of [12] For example, the following is a pure logic program for list membership, where . is cons. 4 8x y:p(x; y) x = F alse) 9v 0 v 1 :x = v 0 :v 1 (y = v 0 p(v 1 ; y) 1) Such programs can be translated to Horn clauses or run directly in a language like Godel [16]. 3.2 Problem Specification As our notion of correctness is equivalence between programs and specifications, our proofs begin with formulas of the form 8x: spec(x) E(x) The variables in x represent parameters to both the specification spec and the logic program E; we do not distinguish input ....

P. Hill and J. Lloyd. The Godel Report. Technical Report TR-91-02, Department of Computer Science, University of Bristol, March 1991. Revised in September 1991.

....systems ( 3] On another hand, an increasing number of works has been developed for embedding sets as a native data structure in high level programming languages, especially logic programming languages [7, 9, 14, 18] their aim is to increase the expressive power of the host language. In [13] for instance, finite intensional sets are allowed : given a predicate definition containing intensional set variables, the resolution mechanism tries to give an explicit representation of these variables. Nevertheless, most previous works deals with finite sets represented by an enumeration of ....

P. M. Hill and John W. Lloyd. The Godel Programming Language. Technical Report CSTR-92-27, Department of Computer Science, University of Bristol, 1992.

....with a fully expressive logical language, however, and so it cannot contain algorithms for computing the appropriate updates; in addition, it does not deal with negative information concluded through closed world reasoning. More recently, the problem has been investigated by Guessoum and Lloyd [4, 5]; but they limit their treatment to definite databases, and so the algorithms they provide do not agree with the semantics of [2] The work that is closest to our own is that of Rossi and Naqvi [9] This work does deal with disjunctive information, and it provides algorithms; however, unlike the ....

A. Guessoum and J. Lloyd. Updating knowledge bases II. Technical Report TR-90-13, Department of Computer Science, University of Bristol (1990).

....with a fully expressive logical language, however, and so it cannot contain algorithms for computing the appropriate updates; in addition, it does not deal with negative information concluded through closed world reasoning. More recently, the problem has been investigated by Guessoum and Lloyd [4, 5]; but they limit their treatment to definite databases, and so the algorithms they provide do not agree with the semantics of [2] The work that is closest to our own is that of Rossi and Naqvi [9] This work does deal with disjunctive information, and it provides algorithms; however, unlike the ....

A. Guessoum and J. Lloyd. Updating knowledge bases. Technical Report TR-89-05, Department of Computer Science, University of Bristol (1989).

....useful information out of the solution. On the other hand, Theorem 6.1 guarantees that each abductive solution generated by SLDNFA is consistent. Equivalently, each disjunct in the generated formula is satisfiable wrt 3 valued completion semantics. Another related procedure has been presented in [18]. This belief revision procedure tries to construct an SLDNF refutation for a given goal by adding facts to the program (as in SLDNFA) to succeed positive goals and by deleting clauses of the program to fail negative goals. We believe that there is a big conceptual gap between this procedure and ....

....the program (as in SLDNFA) to succeed positive goals and by deleting clauses of the program to fail negative goals. We believe that there is a big conceptual gap between this procedure and SLDNFA. They are in general not applicable in the same context. Whether in a given context the procedure in [18] or SLDNFA is applicable depends totally on the reliability of the general domain knowledge which is formulated in the clauses of the program. When reliable, as in planning, no clauses should be retracted and a procedure like SLDNFA should be used. A remaining restriction of SLDNFA is its ....

A. Guessoum and J.W. Lloyd. Updating knowledge bases ii. Technical Report TR-90-13, Department of Computer Science, University of Bristol, 1990.

.... compiler produces code in Prolog, but it would be a relatively straightforward task to produce code in a lower level language; the compiler would then be able to do away with much of the inefficiency normally associated with single assignment languages [8] 5 Another solution, adopted in Godel [5], is to delay evaluation of such expressions. I do not yet fully understand the effects of such a decision on program efficiency and on the adequacy of diagnostic messages. The third implication: it is easier to verify that execution will terminate. The language features various kinds of ....

....in the GAPLOG project [6, 12] Some decisions about types (notably the introduction of the type test statement) are similar in spirit to those in Wirth s Oberon [14] but are in fact carried over from my earlier work on Ground Prolog. The decision to introduce a set type was stolen from Godel [5]. Unfortunately, I read the Godel report too late for that very interesting language to influence my basic design. The fact that Godel and SPILL show some similarities is, perhaps, an indication that I am doing something right. 2 The language The following is a description of SPILL 2 as a ....

Pat M. Hill and John W. Lloyd. The Godel programming language. Technical report CSTR-92-27, Department of Computer Science, University of Bristol, October 1992.

.... qrev(t, x2, z) ALL x y. rev(x, y) qrev(x, y) We are done This theorem states the equivalence of rev and qrev where qrev is defined by the third and fourth assumption. These definitions represent a reverse algorithm that can be run directly in programming languages such as Godel [11], or translated to the following Prolog program: qrev( Y,Z) X1 = append(X1,Y,Z) qrev( H T] Y,Z) X1 = H] append(X1,Y,X2) qrev(T,X2,Z) rev(X,Y) qrev(X, Y) This program is indeed an improvement on the original. Each call to append will execute in constant time since the ....

P. Hill and J. Lloyd. The Godel Report. Technical Report TR-91-02, Department of Computer Science, University of Bristol, March 1991. Revised in September 1991.

....a generative semantics within which disparate information sources can be naturally combined. MDL induction has been successfully applied to a large number of learning problems in the past. Examples include hand printed character recognition [14] decision tree induction [20] molecular evolution [1, 18], analysing dynamic systems [8] learning engineering models [21] clustering [6] computer vision [13] and constructive induction [19] In the context of automated concept acquisition from linguistic corpora, however, applications of the MDL principle have been relatively few. MDL principle has ....

Lloyd Allison. Minimum message length encoding, evolutionary trees and multiple alignment. Technical report, Department of Computer Science, Monash University, Clayton, Victoria, Australia, 1991.

....extensional sets. For instance, 4] is based on a mechanism which constructs an intensional set by enumerating all its elements : the sets are assumed to be finite and abstract set formers are replaced by the corresponding extensional set terms, using a kind of constructive negation mechanism. In [12], finite intensional sets are also allowed : given a predicate definition containing intensional set variables, the resolution mechanism is revisited to give an explicit representation of these variables. Of course, since the finiteness of a first order predicate is a well known undecidable ....

P. M. Hill and John W. Lloyd. The Godel Programming Language. Technical Report CSTR-92-27, Department of Computer Science, University of Bristol, 1992.

.... type variables at the use sites for polymorphic functions 1 [42, 8] Although there is a move away from implicit typing in certain circles of the ML community, it is still popular in the community as a whole and in other language communities such as Miranda 2 , Haskell, l Prolog and Godel [51, 21, 31, 20]. Moreover we may expect implicit typing to play an increasingly important role in scripting languages such as TCL and Python [38, 52] where currently the demands of rapid prototyping and fast development of throw away programs have been used to justify the absence of static typing. Although ....

Pat M. Hill and John W. Lloyd. The Godel programming language. Technical Report CSTR-92-27, Department of Computer Science, University of Bristol, October 1992.

....can be represented directly by means of type declarations. These declarations also define the intended use of the symbols and therefore protect the program from syntactic errors caused by misuse of the symbols. The language on which we have based our ideas is the logic programming language Godel [Hill and Lloyd, 1992]. Godel has a parameterised type system that supports generic but not inclusion polymorphism. Moreover, Godel has a simple module system that supports importation, encapsulation, 1 A shorter version of this paper (without the appendix) will be published in the proceedings for IJCAI 93. 1 and ....

....form W where W is a formula in the language of 5. The declarative semantics of a module free (typed) logic program is based on a typed form of the Clark completion of logic programs using an equality 8 predicate that has declared type (ff; ff) where ff is a parameter. Details can be found in [Hill, 1992] and [Hill and Topor, 1992] 4 A Modular Program: Definition We now define a module (m) 4 and a modular program 5m with main module m 4 . We first define a simple module m which is a module with no import declarations and has import depth 0. It consists of a set fm; Exp; Locg where m is ....

P.M. Hill and J.W. Lloyd. The Godel programming language. Technical Report CSTR-92-27, Department of Computer Science, University of Bristol, UK, 1992.

....semantics is based on SLDNF resolution. 1 Introduction The type system considered here is parametric. Parametric type systems have been described in a number of papers, including [2] 3] 6] 7] 8] 10] 11] and [13] Such a type system is one of the main features of the language Godel [5]. The declarative semantics of untyped logic programs has traditionally been taken to be that of the completion of the program and the procedural semantics to be SLDNF resolution (see [9] Thus it is important to consider how these semantics can be adapted for typed logic programs. It is ....

....rule for definite programs [9, Theorems 8.6, 16.1] the goal A will either have an SLD derivation or a finitely failed SLD tree. It is a simple consequence of [6, Theorems 5.4, 5. 7] that either A or :A is a logical consequence of typed comp(5) 6 Also called the head condition [5], 6] and definitional genericity in [8] 7 Proposition 4.2 Let 5 be a typed definite program with a non trivially typed language. 1. If typed comp(5) is a complete theory wrt to the equations in the language of 5, then the language of 5 satisfies the transparency condition. 2. If typed ....

[Article contains additional citation context not shown here]

P.M. Hill and J.W. Lloyd. The Godel programming language. Technical Report CSTR-92-27, Department of Computer Science, University of Bristol, UK, 1992.

....fib( 20) do write(fibnum) will write no more than the first 20 values produced by the fib generator. 3 Implementation Technique In an effort to make the implementation of our interpreter capable of modeling a variety of control mechanisms, we have used a well known implementation technique [All88][HF86] KH89] Ste78] known as continuation passingstyle. This technique has been shown to be flexible enough to implement a large spectrum of mechanisms from simple if expressions to catch throw and coroutine mechanisms. This style of programming builds functions during language interpretation and ....

Lloyd Allison. Continuations Implement Generators and Streams. Technical Report 88/112, Department of Computer Science, Monash University, August 1988.

No context found.

P. Hill and J. Lloyd. The Godel report. Technical Report TR-91-02, Department of Computer Science, University of Bristol, March 1991.

First 50 documents

Online articles have much greater impact   More about CiteSeer.IST   Add search form to your site   Submit documents   Feedback  

CiteSeer.IST - Copyright Penn State and NEC