A Tractable Extension of Linear Indexed Grammars

It has been shown that Linear Indexed Grammars can be processed in polynomial time by exploiting constraints which make possible the extensive use of structure-sharing. This paper describes a formalism that is more powerful than Linear Indexed Grammar, but which can also be processed in polynomial time using similar techniques. The formalism, which we refer to as Partially Linear PATR manipulates feature structures rather than stacks.Comment: 8 pages LaTeX, uses eaclap.sty, to appear in EACL-9

Combinator evaluation of functional programs with logical variables

technical reportA technique is presented that brings logical variables into the scope of the well known Turner method for evaluating normal order functioned programs by S, K, I combinator graph reduction. This extension is illustrated by SASL+LV, an extension of Turner's language SASL in which general expressions serve as formal parameters, and parameter passage is done by unification. The conceptual and practical advantages of such an extension are discussed, as well as semantic pitfalls that arise from the attendant weakening of referential transparency. Only four new combinators (LV, BV, FN and UNIFY) are introduced. The resulting object code is fully upward compatible in the sense that previously compiled SASL object code remains executable with unchanged semantics. However, "read-only" variable usage in SASL-f LV programs requires a "multi-tasking" extension of the customary stack-based evaluation method. Mechanisms are presented for managing this multi-tasking on both single and multi-processor systems. Finally, directions are examined for applying this technique to implementations involving larger granularity combinators, and fuller semantic treatment of logical variables (e.g. accommodation of failing unifications)

Parallel Natural Language Parsing: From Analysis to Speedup

Electrical Engineering, Mathematics and Computer Scienc

Granularity in Large-Scale Parallel Functional Programming

This thesis demonstrates how to reduce the runtime of large non-strict functional programs using parallel evaluation. The parallelisation of several programs shows the importance of granularity, i.e. the computation costs of program expressions. The aspect of granularity is studied both on a practical level, by presenting and measuring runtime granularity improvement mechanisms, and at a more formal level, by devising a static granularity analysis. By parallelising several large functional programs this thesis demonstrates for the first time the advantages of combining lazy and parallel evaluation on a large scale: laziness aids modularity, while parallelism reduces runtime. One of the parallel programs is the Lolita system which, with more than 47,000 lines of code, is the largest existing parallel non-strict functional program. A new mechanism for parallel programming, evaluation strategies, to which this thesis contributes, is shown to be useful in this parallelisation. Evaluation strategies simplify parallel programming by separating algorithmic code from code specifying dynamic behaviour. For large programs the abstraction provided by functions is maintained by using a data-oriented style of parallelism, which defines parallelism over intermediate data structures rather than inside the functions. A highly parameterised simulator, GRANSIM, has been constructed collaboratively and is discussed in detail in this thesis. GRANSIM is a tool for architecture-independent parallelisation and a testbed for implementing runtime-system features of the parallel graph reduction model. By providing an idealised as well as an accurate model of the underlying parallel machine, GRANSIM has proven to be an essential part of an integrated parallel software engineering environment. Several parallel runtime- system features, such as granularity improvement mechanisms, have been tested via GRANSIM. It is publicly available and in active use at several universities worldwide. In order to provide granularity information this thesis presents an inference-based static granularity analysis. This analysis combines two existing analyses, one for cost and one for size information. It determines an upper bound for the computation costs of evaluating an expression in a simple strict higher-order language. By exposing recurrences during cost reconstruction and using a library of recurrences and their closed forms, it is possible to infer the costs for some recursive functions. The possible performance improvements are assessed by measuring the parallel performance of a hand-analysed and annotated program

1st doctoral symposium of the international conference on software language engineering (SLE) : collected research abstracts, October 11, 2010, Eindhoven, The Netherlands

The first Doctoral Symposium to be organised by the series of International Conferences on Software Language Engineering (SLE) will be held on October 11, 2010 in Eindhoven, as part of the 3rd instance of SLE. This conference series aims to integrate the different sub-communities of the software-language engineering community to foster cross-fertilisation and strengthen research overall. The Doctoral Symposium at SLE 2010 aims to contribute towards these goals by providing a forum for both early and late-stage Ph.D. students to present their research and get detailed feedback and advice from researchers both in and out of their particular research area. Consequently, the main objectives of this event are: – to give Ph.D. students an opportunity to write about and present their research; – to provide Ph.D. students with constructive feedback from their peers and from established researchers in their own and in different SLE sub-communities; – to build bridges for potential research collaboration; and – to foster integrated thinking about SLE challenges across sub-communities. All Ph.D. students participating in the Doctoral Symposium submitted an extended abstract describing their doctoral research. Based on a good set of submisssions we were able to accept 13 submissions for participation in the Doctoral Symposium. These proceedings present final revised versions of these accepted research abstracts. We are particularly happy to note that submissions to the Doctoral Symposium covered a wide range of SLE topics drawn from all SLE sub-communities. In selecting submissions for the Doctoral Symposium, we were supported by the members of the Doctoral-Symposium Selection Committee (SC), representing senior researchers from all areas of the SLE community.We would like to thank them for their substantial effort, without which this Doctoral Symposium would not have been possible. Throughout, they have provided reviews that go beyond the normal format of a review being extra careful in pointing out potential areas of improvement of the research or its presentation. Hopefully, these reviews themselves will already contribute substantially towards the goals of the symposium and help students improve and advance their work. Furthermore, all submitting students were also asked to provide two reviews for other submissions. The members of the SC went out of their way to comment on the quality of these reviews helping students improve their reviewing skills

1st doctoral symposium of the international conference on software language engineering (SLE) : collected research abstracts, October 11, 2010, Eindhoven, The Netherlands

The first Doctoral Symposium to be organised by the series of International Conferences on Software Language Engineering (SLE) will be held on October 11, 2010 in Eindhoven, as part of the 3rd instance of SLE. This conference series aims to integrate the different sub-communities of the software-language engineering community to foster cross-fertilisation and strengthen research overall. The Doctoral Symposium at SLE 2010 aims to contribute towards these goals by providing a forum for both early and late-stage Ph.D. students to present their research and get detailed feedback and advice from researchers both in and out of their particular research area. Consequently, the main objectives of this event are: – to give Ph.D. students an opportunity to write about and present their research; – to provide Ph.D. students with constructive feedback from their peers and from established researchers in their own and in different SLE sub-communities; – to build bridges for potential research collaboration; and – to foster integrated thinking about SLE challenges across sub-communities. All Ph.D. students participating in the Doctoral Symposium submitted an extended abstract describing their doctoral research. Based on a good set of submisssions we were able to accept 13 submissions for participation in the Doctoral Symposium. These proceedings present final revised versions of these accepted research abstracts. We are particularly happy to note that submissions to the Doctoral Symposium covered a wide range of SLE topics drawn from all SLE sub-communities. In selecting submissions for the Doctoral Symposium, we were supported by the members of the Doctoral-Symposium Selection Committee (SC), representing senior researchers from all areas of the SLE community.We would like to thank them for their substantial effort, without which this Doctoral Symposium would not have been possible. Throughout, they have provided reviews that go beyond the normal format of a review being extra careful in pointing out potential areas of improvement of the research or its presentation. Hopefully, these reviews themselves will already contribute substantially towards the goals of the symposium and help students improve and advance their work. Furthermore, all submitting students were also asked to provide two reviews for other submissions. The members of the SC went out of their way to comment on the quality of these reviews helping students improve their reviewing skills

Parallel processing and expert systems

Whether it be monitoring the thermal subsystem of Space Station Freedom, or controlling the navigation of the autonomous rover on Mars, NASA missions in the 1990s cannot enjoy an increased level of autonomy without the efficient implementation of expert systems. Merely increasing the computational speed of uniprocessors may not be able to guarantee that real-time demands are met for larger systems. Speedup via parallel processing must be pursued alongside the optimization of sequential implementations. Prototypes of parallel expert systems have been built at universities and industrial laboratories in the U.S. and Japan. The state-of-the-art research in progress related to parallel execution of expert systems is surveyed. The survey discusses multiprocessors for expert systems, parallel languages for symbolic computations, and mapping expert systems to multiprocessors. Results to date indicate that the parallelism achieved for these systems is small. The main reasons are (1) the body of knowledge applicable in any given situation and the amount of computation executed by each rule firing are small, (2) dividing the problem solving process into relatively independent partitions is difficult, and (3) implementation decisions that enable expert systems to be incrementally refined hamper compile-time optimization. In order to obtain greater speedups, data parallelism and application parallelism must be exploited

Verification and Application of Program Transformations

A programtranszformáció és a refaktorálás alapvető elemei a szoftverfejlesztési folyamatnak. A refaktorálást a kezdetektől próbálják szoftvereszközökkel támogatni, amelyek megbízhatóan és hatékonyan valósítják meg a szoftverminőséget javító, a működést nem érintő programtranszformációkat. A statikus elemzésre alapuló hibakeresés és a refaktorálási transzformációk az akadémiában és a kutatás-fejlesztésben is nagy érdeklődésre tartanak számot, ám még ennél is fontosabb a szerepük a nagy bonyolultságú szoftvereket készítő vállalatoknál. Egyre pontosabbak és megbízhatóbbak a szoftverfejlesztést támogató eszközök, de bőven van még min javítani. A disszertáció olyan definíciós és verifikációs módszereket tárgyal, amelyekkel megbízhatóbb és szélesebb körben használt programtranszformációs eszközöket tudunk készíteni. A dolgozat a statikus és a dinamikus verifikációt is érinti. Elsőként egy újszerű, tömör leíró nyelvet mutat be L-attribútum grammatikákhoz, amelyet tulajdonságalapú teszteléshez használt véletlenszerű adatgenerátorra képezünk le. Ehhez egy esettanulmány társul, amely az Erlang programozási nyelv grammatikáját, majd a teszteléshez való felhasználását mutatja be. A tesztelés mellett a formális helyességbizonyítás kérdését is vizsgáljuk, ehhez bevezetünk egy refaktorálások leírására szolgáló nyelvet, amelyben végrehajtható és automatikusan bizonyítható specifikációkat tudunk megadni. A nyelv környezetfüggő és feltételes termátíráson, stratégiákon és úgynevezett refaktorálási sémákon alapszik. Végül, de nem utolsó sorban a programtranszformációk egy speciális alkalmazása kerül bemutatásra, amikor egy refaktoráló keretrendszert előfordítóként használunk a feldolgozott programozási nyelv kiterjesztésére. Utóbbi módszerrel könnyen implementálható az Erlang nyelvben a kódmigráció

Executable Attribute Grammars for Modular and Efficient Natural Language Processing

Language-processors that are constructed using top-down recursive-descent with backtracking parsing are highly modular, and are easy to implement and maintain. However, a widely-held inaccurate view is that top-down processors are inherently exponential for ambiguous grammars and cannot accommodate left-recursive syntax rules. It has been known that exponential time and space complexities can be avoided by memoization and compact graph-structured representation, and that left- recursive productions can be accommodated through a variety of techniques. However, until now, memoization, compact representation, and techniques for handling left-recursion have either been presented independently, or else attempts at their integration have compromised modularity and correctness of the resulting parses. Specifying syntax and semantics to describe formal languages using denotational notation of attribute grammars (AGs) has been widely practiced. However, very little work has shown the usefulness of declarative AGs for constructing computational models of natural language. Previous top-down approaches fall short in accommodating ambiguous and general CFGs with arbitrary semantics in one pass as executable specifications. Existing approaches lack in providing a declarative syntax-semantics interface that can take full advantages of dependencies between attributes of syntactic constituents to model linguistically-motivated cases. This thesis solves these shortcomings by proposing a new modular top-down syntactic and semantic analysis system, which is efficient and accommodates all forms of CFGs. Moreover, this system provides notation to declaratively specify semantics by establishing arbitrary dependencies between attributes of syntactic categories to perform linguistically-motivated tasks such as: building directly-executable natural-language query processors, computing meanings of sentences using compositional semantics, performing contextual disambiguation tasks, modelling restrictive classes of languages etc