David T. Barnard

Design, Analysis, and Implementation of a Parallel Tree Search Algorithm

The alpha-beta algorithm for searching decision trees is adapted to allow parallel activity in different parts of a tree during the search. The algorithm has been implemented in a procedural simulation language (GASP IV). The simulation environment provides the illusion of multiple software processes and multiple hardware processors. A number of preliminary experiments have been done to gather statistics on run time, nodes scored, and nodes visited. Results indicate that a substantial reduction in time of search occurs because of the use of parallelism. An analytic expression for the storage requirements of the algorithm is derived. The analysis provides an example of the classical tradeoff between time and storage.

SP/k: a system for teaching computer programming

SP/k is a compatible subset of the PL/I language that has been designed for teaching programming. The features of the SP/k language were chosen to encourage structured problem solving by computers, to make the language easy to learn and use, to eliminate confusing and redundant constructs, and to make the language easy to compile. The resulting language is suitable for introducing programming concepts used in various applications, including business data processing, scientific calculations and non-numeric computation. SP/k is actually a sequence of language subsets called SP/1, SP/2, … SP/8. Each subset introduces new programming language constructs while retaining all the constructs of preceding subsets. Each subset is precisely defined and can be learned or implemented without the following subsets.

Hierarchical encoding of text: Technical problems and SGML solutions

One recurring theme in the TEI project has been the need to represent non-hierarchical information in a natural way — or at least in a way that is acceptable to those who must use it — using a technical tool that assumes a single hierarchical representation. This paper proposes solutions to a variety of such problems: the encoding of segments which do not reflect a documents primary hierarchy; relationships among non-adjacent segments of texts; ambiguous content; overlapping structures; parallel structures; cross-references; vague locations.

SGML-Based Markup for Literary Texts: Two Problems and Some Solutions

There is wide agreement on the need for a markup standard for encoding literary texts. The Standard Generalized Markup Language (SGML) seems to provide the best basis for such a standard. But two problems inhibit the acceptance of SGML for this purpose. (1) Computer-assisted textual studies often require the maintenance of multiple views of a documents structure, but SGML is not designed to accommodate such views. (2) An SGML-based standard would appear to entail the keyboarding of more markup than researchers are accustomed to, or are likely to accept. We discuss five ways of dealing with the first problem, and several ways of reducing the burden of markup. We conclude that the problem of maintaining multiple views can be surmounted, though with some difficulty, and that the markup required for an SGML-based standard can be reduced to a level comparable to that of other markup schemes currently in use.Ron Hayter is the Senior Software Developer of Software Exoterica Corporation, Ottawa, Canada.Maria Karibaba obtained the M.Sc. degree in Computing and Information Science at Queens University and returned to Greece.George Logan is Head of the Department of English at Queens University, Canada.John McFadden is the President of Software Exoterica Corporation, Ottawa, Canada

Hierarchic syntax error repair for LR grammars

A description of a technique for handling syntax errors in compilers, called hierarchic error repair, is presented. The technique is simple to understand and to implement. It always repairs a source program into a syntactically valid program and never causes the parser to back up. Details of embedding the technique in the LR family of parsers are given.

Holophrasted displays in an interactive environment

Abstract This article presents a general algorithm for prettyprinting and holophrasting interactively created objects. It is shown how an environment with knowledge of the entities it manipulates can automatically produce cathode-ray tube displays with more helpful contextual information for the user than a traditional display of contiguous lines from a source file.

Parallel parsing on the connection machine

Abstract We show that languages generated by LL(1) grammars can be parsed in logarithmic time on the Connection Machine. The algorithm extends a lexing algorithm of Hillis et al. and demonstrates that the widely-held supposition that parsing is inherently linear is false.

Producing a top-down parse order with bottom-up parsing

An adaptation of the standard LR(1) and LALR(1) parsing algorithm is described such that a top-down parse order is produced rather than the standard bottom-up order.

SL parses the LR languages

Abstract SL, the Syntax Language component of S/SL (Syntax/Semantic Language) is a dataless programming language for implementing efficient recursive descent parsers. SL is clearly powerful enough to parse the LL(1) languages, but it is much less obvious that it is sufficiently powerful to parse the LR( k ) languages. We show that this is in fact the case by giving an algorithm to construct an SL program that parses the same language as a given LR(1) parser. This construction provides both a proof that SL has the parsing power of LR(1) [and hence LR( k )] and a practical method for deriving efficient SL parsers from BNF grammars.

The text encoding initiative: flexible and extensible document encoding

The Text Encoding Initiative is an international collaboration aimed at producing a common encoding scheme for complex texts. The diversity of the texts used by members of the communities served by the project led to a large specification, but the specification is structured to facilitate understanding and use. The requirement for generality is sometimes in tension with the requirement to handle specialized text types. The texts that are encoded often can be viewed or interpreted in several different ways. While many electronic documents can be encoded in very simple ways, some documents and some users will tax the limits of any fixed scheme, so a flexible extensible encoding is required to support research and to facilitate the reuse of texts.