. A sparse suffix tree is a suffix tree that represents only a subset of the suffixes of the text. This is in contrast to the standard suffix tree that represents all suffixes. By selecting a small enough subset, a sparse suffix tree can be made to fit the available storage, unfortunately at the cost of increased search times. The idea of sparse suffix trees goes back to PATRICIA tries. Evenly spaced sparse suffix trees represent every kth suffix of the text. In the paper, we give general construction and search algorithms for evenly spaced sparse suffix trees, and present their run time analysis, both in the worst and in the average case. The algorithms are further improved by using so-called dual suffix trees. 1 Introduction Finding an index for a long text that makes fast string matching possible is one of the very central problems of text processing systems. Suffix trees offer a theoretically time-optimal solution. A suffix tree is a trie-like data structure that represents all su...

This thesis presents a new architecture for information discovery based on a hierarchy of content routers that provide both browsing and search services to end users. Content routers catalog information servers, which may in turn be other content routers. The resulting hierarchy of content routers and leaf servers provides a rich set of services to end users for locating information, including query refinement and query routing. Query refinement helps a user improve a query fragment to describe the user's interests more precisely. Once a query has been refined and describes a manageable result set, query routing automatically forwards the query to relevant servers. These services make use of succinct descriptions of server contents called content labels. A unique contribution of this research is the demonstration of a scalable discovery architecture based on a hierarchical approach to routing.

Over the past several years, a number of information discovery and access tools have been introduced in the Internet, including Archie, Gopher, Netfind, and WAIS. These tools have become quite popular, and are helping to redefine how people think about wide area network applications. Yet, they are not well suited to supporting the future information infrastructure, which will be characterized by enormous data volume, rapid growth in the user base, and burgeoning data diversity. In this paper we indicate trends in these three dimensions, and survey problems these trends will create for current approaches. We then suggest several promising directions of future resource discovery research, along with some initial results from projects carried out by members of the Internet Research Task Force Research Group on Resource Discovery and Directory Service.

Query languages of full text retrieval systems are based on several assumptions about the input text. Many systems assume that the input has some basic structure (say, documents and words) which restricts the application domain. Others only allow to retrieve documents and not text positions. We address these problems and we propose an extended model for text, and a query language based on it. The query language is powerful enough to be used as an intermediate language to customized and/or intelligent retrieval applications based on visual interfaces. We also discuss several implementation issues giving preliminary experimental results. Keywords: Text databases, query languages. 1 Introduction Full text retrieval systems are becoming a popular way of providing support for on-line text. Their advantage is that they avoid the complicated and expensive process of semantic indexing. From the end-user point of view, full text searching of on-line documents is appealing because a valid quer...