The time cost of searching with an inverted index is directly proportional to the number of postings processed and the cost of processing each posting. Dynamic pruning reduces the number of postings examined. Pre-calculation then quantization of term / document weights reduces the cost of evaluating each posting. The effect of quantization on precision, latency, and index size is examined herein. We show empirically that there is an ideal size (in bits) for storing the quantized scores. Increasing this adversely affects index size and search latency; decreasing it adversely affects precision. We observe a relationship between the collection size and ideal quantization size, and provide a way to determine the number of bits to use from the collection size.

Abstract Coding standards and good practices are fundamental to a disciplined approach to software projects irrespective of programing languages being employed. Prolog programing can benefit from such an approach, perhaps more than programing in other languages. Despite this, no widely accepted standards and practices seem to have emerged till now. The present paper is a first step toward filling this void: It provides immediate guidelines for code layout, naming conventions, documentation, proper use of Prolog features, program development, debugging, and testing. Presented with each guideline is its rationale and, where sensible options exist, illustrations of the relative pros and cons for each alternative. A coding standard should always be selected on a per-project basis, based on a host of issues pertinent to any given programing project; for this reason the paper goes beyond the mere provision of normative guidelines by discussing key factors and important criteria that should be taken into account when deciding on a full-fledged coding standard for the project.

Operating systems only provide general-purpose I/O optimisation since they have to service various types of applications. However, application level I/O optimisation can achieve better performance since an application has a better knowledge of how to optimise disk I/O for the application. In this paper we provide a solution for application-specific I/O for optimising a search engine. It shows a 28% improvement when compared to the general-purpose I/O optimisation of Linux. Our result also shows a 11% improvement when the Linux I/O optimisation is bypassed.

Imperative programmers often use cyclically linked trees in order to achieve O(1) navigation time to neighbours. Some logic programmers believe that cyclic terms are necessary to achieve the same in logic-based languages. An old but little-known technique provides O(1) time and space navigation without cyclic links, in the form of reversible predicates. A small modification provides O(1) amortised time and space editing.