Abstract
The effectiveness and efficiency of searches for relevant documents strongly depend on key features of the descriptor language supported by the retrieval system. Effectiveness, for instance, is limited by the expressiveness of the descriptors. In addition, system efficiency is proportional to tractability. Furthermore, user effort is relative to comprehensibility and compactness. From a formulation point of view, compactness allows a high degree of integration, combining several occurrences of an analogous concept in a single expression. A proper descriptor language for information discovery should thus find a workable balance between these features. Boolean index expressions (BIEs) are proposed as balanced descriptors for the communication of information needs. Compared to many other descriptor languages, an advantage of BIEs is their compactness, offering the opportunity to convey much information in a succinct way. The goal of this article is to investigate compactness of BIEs. For instance, we analyse how compactness is brought about in BIEs and how it can be effectively measured. In addition, two classes of BIEs are investigated that illustrate the bounds on the compactness of BIEs: minimal and maximal BIEs. The bounds are explicitly derived and illustrated by generic examples. Furthermore, we report on experiments that ascertain the merit of minimal and maximal BIEs
