This paper argues that comprehensions, a construct found in some programming languages, are a good query notation for DBPLs. It is shown that, like many other query notations, comprehensions can be smoothly integrated into DBPLs and allow queries to be expressed clearly, concisely and efficiently. More significantly, two advantages of comprehensions are demonstrated. The first advantage is that, unlike conventional notations, comprehension queries combine computational power with ease of optimisation. That is, not only can comprehension queries express both recursion and computation, but equivalent comprehension transformations exist for all of the major conventional optimisations. The second advantage is that comprehensions provide a uniform notation for expressing and performing some optimisation on queries over several bulk data types. The bulk types that comprehensions can be defined over include sets, relations, bags and lists. A DBPL can also be automatically extended to provide and partially optimise comprehension queries over new bulk types constructed by the application programmer, providing that the new type has some well-defined properties. 1

A Functional Database Phil Trinder D.Phil. Thesis Wolfson College Michaelmas Term, 1989 This thesis explores the use of functional languages to implement, manipulate and query databases. Implementing databases. A functional language is used to construct a database manager that allows efficient and concurrent access to shared data. In contrast to the locking mechanism found in conventional databases, the functional database uses data dependency to provide exclusion. Results obtained from a prototype database demonstrate that data dependency permits an unusual degree of concurrency between operations on the data. The prototype database is used to exhibit some problems that seriously restrict concurrency and also to demonstrate the resolution of these problems using a new primitive. The design of a more realistic database is outlined. Some restrictions on the data structures that can be used in a functional database are also uncovered. Manipulating databases. Functions over the database a...

ly this simulation model is just a M/M/s queue.] This bank simulation program consists of a teller resource and two process specification procedures. These procedures provide a script or template for created processes. The Generator process (the single process created from the Generator process specification procedure) is used to create Poisson arrivals of Customer processes. The Customer process specification procedure encodes a script for a typical customer. A customer requests a teller. If one is not available, the customer waits in the teller queue. Once the customer has a teller, he is served for an exponentially distributed amount of time. Finally, the customer relinquishes the teller and leaves the bank. [Note, Wirth's InOut I/O module is somewhat weak and inconvenient, so we wrote our own (PascalIO) whose flavor is closer to I/O in Pascal. The letter after the word WRITE is the first letter of the data type being written.] After the program listing, output results generated fro...

Information systems (IS) development approaches are considered with particular reference to information requirements analysis. The majority can be classified as adopting a unitary, objective perspective. This fails to fully recognise the interpretative, inter-subjective nature of information and the importance of informal as well as formal data processing systems. This paper aims to contribute to the discussion on tools and methods for systems development by providing a contrasting perspective on information requirements analysis as a process which is socially mediated. A framework is developed which places information requirements in the context strategic IS development. This features social communication networks centrally in this process and raises implications for practice in IS development. 1. Background There has been considerable emphasis in the literature on information systems (IS) development on using structured approaches as a means of identifying information requirements for systems development. An assumption underpinning such approaches is that formal, Information Technology-based data processing systems are the medium through which information requirements can be best met (c.f. Avison and Fitzgerald, [1]. This is so, despite the fact that authors in the IS field [2] and in the field of organization theory [3] have long emphasised the significance of the informal, political and interpretative aspects of information. The aim of this paper is to contribute to the discussion of automated tools in IS development by providing a contrasting perspective on information requirements analysis as being socially mediated and thereby requiring awareness of the socio-political aspects of the IS development process and associated techniques. The paper argues that such a perspective might usefully complement the more formal, automated tools and

this paper a single-step threshold search algorithm and its optical implementation. The proposed algorithm performs magnitude comparison in constant time, independent of the operand size, and consequently, it greatly increases the performance of optical database/knowledge-base processing operations such as searching, selection, retrieving, and sorting.

highly dependent on word size. One magnitude-comparison algorithm 9 succeeds in achieving word and bit parallelism, but it requires that multiple comparands be processed in serial fashion. In this Letter we present an algorithm and architecture that perform magnitude- comparison processing in a multiple-comparand word-parallel (many words compared with many words) and bit-parallel (many bits compared simultaneously) manner. Binary patterns are represented by spatially distributed orthogonally polarized locations on a twodimensional pixelated grid. We define logical 1 as vertically polarized light and logical 0 as horizontally polarized light. Individual tuples are differentiated from each other by polarization encoding of each to a unique wavelength. Only the comparison of a single comparand with a single tuple is shown for clarity and graphical simplicity. The output of this system is a register that indicates the relative magnitude of n number of com