David W. Stemple

Human factors comparison of a procedural and a nonprocedural query language

Two experiments testing the ability of subjects to write queries in two different query languages were run. The two languages, SQL and TABLET, differ primarily in their procedurality; both languages use the relational data model, and their Halstead levels are similar. Constructs in the languages which do not affect their procedurality are identical. The two languages were learned by the experimental subjects almost exclusively from manuals presenting the same examples and problems ordered identically for both languages. The results of the experiments show that subjects using the more procedural language wrote difficult queries better than subjects using the less procedural language. The results of the experiments are also used to compare corresponding constructs in the two languages and to recommend improvements for these constructs.

Automatic verification of database transaction safety

Maintaining the integrity of databases is one of the promises of database management systems. This includes assuring that integrity constraints are invariants of database transactions. This is very difficult to accomplish efficiently in the presence of complex constraints and large amounts of data. One way to minimize the amount of processing required to maintain database integrity over transaction processing is to prove at compile-time that transactions cannot, if run atomically, disobey integrity constraints. We report on a system that performs such verification for a robust set of constraint and transaction classes. The system accepts database schemas written in a more or less traditional style and accepts programs in a high-level programming language. Automatic verification fast enough to be effective on current workstation hardware is performed.

Recommended curriculum for CS2, 1984: a report of the ACM curriculum task force for CS2

A Report of the ACM Curriculum Task Force for CS2

Type-Safe Linguistic Reflection: A Generator Technology

Reflective systems allow their own structures to be altered from within. In a programming system reflection can occur in two ways: by a program altering its own interpretation or by it changing itself. Reflection has been used to facilitate the production and evolution of data and programs in database and programming language systems. This paper is concerned with a particular style of reflection, called linguistic reflection, used in compiled, strongly typed languages. Two major techniques for this have evolved: compile-time reflection and run-time reflection. These techniques are described together with a definition and anatomy of reflective systems using them. Two illustrative examples are given and the uses of type-safe reflective techniques in a database programming language context are surveyed. These include attaining high levels of genericity, accommodating changes in systems, implementing data models, optimising implementations and validating specifications.

Exceeding the limits of polymorphism in database programming languages

Database programming languages represent an attempt to merge the technologies of programming languages and database management in order to improve the development of data-intensive applications. One aspect of the research on database programming languages is an attempt to exploit polymorphism and higher order functions to integrate query algebra capabilities into programming languages. This has proved to be difficult especially in strongly and statically typed languages, due to the high level of polymorphism and reflection in database query languages. For example, the natural join operation of relational algebra requires examination of the types of the input relations to determine the match predicate and output type, neither of which are easily expressed in current polymorphic programming languages. These aspects of natural join require quite sophisticated polymorphism and some kind of reflection. The reflection must be powerful enough to allow the examination of the input types to determine the match function and to synthesize the output type. It is the difficulty in achieving such power parsimoniously that we examine in this paper.

Linguistic reflection in Java

This work is partially supported by the EPSRC through Grant GR/J 67611 ‘Delivering the Benefits of Persistence to System Construction’

Sedentary life style of Neotropical sedge wrens promotes song imitation

To what extent has the style of song development among songbirds coevolved with other life history strategies? Among Cistothorus wrens in North America, it seems that sedentary or site-faithful habits of marsh wrens, C. palustris, favour song imitation, but seminomadic habits of sedge wrens, C. platensis, favour song improvisation, whereby each male generates a large but unique song repertoire. In this study, we tested whether more sedentary populations of sedge wrens in the Neotropics would imitate songs. At our primary study site near Cartago, Costa Rica, breeding birds were colour-banded during 1995 and 1996, and follow-up surveys revealed that the birds remained at this site the year round. Extensive tape recording and analysis of songs showed that males had large song repertoires (200-300+ songs), and that many songs were shared among neighbouring males. In addition, males only 27 km distant, at La Pastora, used different songs. Furthermore, matched countersinging, in which two males answer each other with identical song types, was recorded near Brasilia, in Brazil. The sharing of songs among permanent neighbours, microgeographical variation in song, and matched countersinging can be achieved only through song imitation, thus revealing a striking difference in the style of song development among different populations of the sedge wren. In the Neotropics, having predictable neighbours throughout life appears to have favoured song imitation, so that individuals can interact using a common, learned code typical of the local population; among more mobile populations in North America, however, individuals improvise large repertoires of species-typical songs, thereby enabling singing males to communicate with any individual, no matter what the population of origin. Strategies of song development must correlate with life history features, and further surveys are needed to make sense of the great diversity of singing behaviours among songbirds. Copyright 1999 The Association for the Study of Animal Behaviour.

Specifying Flexible Concurrency Control Schemes: an Abstract Operational Approach

An abstract, operational model for specifying flexible concurrency control schemes within a persistent store is presented. The goal of the model is to allow concurrency control schemes to be specified in a manner that promotes understandability and supports their implementation. Schemes that support controlled sharing among autonomous computations are the primary targets of this work. An abstract machine programmed by a set of rules is employed to specify operational semantics for the concurrency control schemes.

On the modes and meaning of feedback to transaction designers

An analysis of database transactions in the presence of database integrity constraints can lead to several modes of feedback to transaction designers. The different kinds of feedback include tests and updates that could be added to the transaction to make it obey the integrity constraints, as well as predicates representing post-conditions guaranteed by a transactions execution. We discuss the various modes, meanings, and uses of feedback. We also discuss methods of generating feedback from integrity constraints, transaction details and theorems constituting both generic knowledge of database systems and specific knowledge about a particular database. Our methods are based on a running system that generates tailored theories about database systems from their schemas and uses these theories to prove that transactions obey integrity constraints.

Concurrent Shadow Paging in the Flask Architecture

The differing requirements for concurrency models in programming languages and databases are widely diverse and often seemingly incompatible. The rigid provision of a particular concurrency control scheme in a persistent object system limits its usefulness to a particular class of applications, in contrast to the generality intended by the provision of persistence. One solution is to provide a flexible system in which concurrency control schemes may be specified according to the particular task in hand, allowing the same data to be used in conjunction with different concurrency control schemes according to the needs of the application.