The problem of answering queries using views is to find efficient methods of answering a query using a set of previously defined materialized views over the database, rather than accessing the database relations. The problem has recently received significant attention because of its relevance to a wide variety of data management problems. In query optimization, finding a rewriting of a query using a set of materialized views can yield a more efficient query execution plan. To support the separation of the logical and physical views of data, a storage schema can be described using views over the logical schema. As a result, finding a query execution plan that accesses the storage amounts to solving the problem of answering queries using views. Finally, the problem arises in data integration systems, where data sources can be described as precomputed views over a mediated schema. This article surveys the state of the art on the problem of answering queries using views, and synthesizes the disparate works into a coherent framework. We describe the different applications of the problem, the algorithms proposed to solve it and the relevant theoretical results.

: The web harbors a large number of communities -- groups of content-creators sharing a common interest -- each of which manifests itself as a set of interlinked web pages. Newgroups and commercial web directories together contain of the order of 20000 such communities; our particular interest here is on emerging communities -- those that have little or no representation in such fora. The subject of this paper is the systematic enumeration of over 100,000 such emerging communities from a web crawl: we call our process trawling. We motivate a graph-theoretic approach to locating such communities, and describe the algorithms, and the algorithmic engineering necessary to find structures that subscribe to this notion, the challenges in handling such a huge data set, and the results of our experiment. Keywords: web mining, communities, trawling, link analysis 1. Overview The web has several thousand well-known, explicitly-defined communities -- groups of individuals who share a common int...

Abstract not found

Current-day crawlers retrieve content only from the publicly indexable Web, i.e., the set of web pages reachable purely by following hypertext links, ignoring search forms and pages that require authorization or prior registration.

ions Implementation-level: pages, links, presentation styles Reuse Plug-in components; Reusable presentation styles Architecture Two-tiers, based on file system Static binding of content to pages Usability High graphical control through manual authoring High coherence through use of presentation styles Low customization, no adaptivity, no proactivity 236 . P. Fraternali ACM Computing Surveys, Vol. 31, No. 3, September 1999 metaphor (e.g., in Director, objects' synchronization is defined by editing the score for the cast members of a stage; see Figure 6). ---The type of database connectivity, which may range from support of an internal database, of an external database via gateway software (typically ODBC or JDBC), or of an external database through DBMS API. ---The type of Web connectivity, which may be achieved by means of a plug-in application extending a Web browser, or by exporting the hypermedia application into a network language. Web connectivity may affect database c...

The subject of this paper is the creation of knowledge bases by enumerating and organizing all web occurrences of certain subgraphs. We focus on subgraphs that are signatures of web phenomena such as tightly-focused topic communities, webrings, taxonomy trees, keiretsus, etc. For instance, the signature of a webring is a central page with bidirectional links to a number of other pages. We develop novel algorithms for such enumeration problems. A key technical contribution is the development of a model for the evolution of the web graph, based on experimental observations derived from a snapshot of the web. We argue that our algorithms run efficiently in this model, and use the model to explain some statistical phenomena on the web that emerged during our experiments. Finally, we describe the design and implementation of Campfire, a knowledge base of over one hundred thousand web communities. 1 Overview The subject of this paper is the creation of knowledge bases by ...

Peer data management systems (PDMS) offer a flexible architecture for decentralized data sharing. In a PDMS, every peer is associated with a schema that represents the peer's domain of interest, and semantic relationships between peers are provided locally between pairs (or small sets) of peers. By traversing semantic paths of mappings, a query over one peer can obtain relevant data from any reachable peer in the network. Semantic paths are traversed by reformulating queries at a peer into queries on its neighbors. Naively following semantic paths...

Due to the availability on the Internet of a wide variety of sources of information on closely related topics, the problem of providing seamless, integrated access to such sources has become (again) a major research challenge. Although this problem has been studied for several decades, especially in the database community, there is a need for a more refined approach in those cases where the original sources maintain their own independent view of the world. In particular, we motivate with examples the utility of directed non-injective mappings between the individuals in the domains of multiple Information Sources.

We present a new formal model of query and computation on the Web. We focus on two important aspects that distinguish the access to Web data from the access to a standard database system: the navigational nature of the access and the lack of concurrency control. We show that these two issues have significant effects on the computability of queries. To illustrate the ideas and how they can be used in practice for designing appropriate Web query languages, we consider a particular query language, the Web calculus, an abstraction and extension of the practical Web query language WebSQL. c fl1998 Elsevier Science Ltd. All rights reserved Key words: World Wide Web, Web Queries, Query Languages, Computability, Formal Models 1. INTRODUCTION Tools and techniques for retrieving information from the World Wide Web are rapidly being developed [9, 10, 13, 4, 12, 8]. Most of these works are based on the metaphor of the Web as a database, in order to carry over and adapt familiar query languages s...

... In this paper, we describe the way the expressive power of the Carin language is exploited in the Picsel information integration system, while maintaining the decidability of query answering. We illustrate it on examples coming from the tourism domain, which is the first real case that we have to consider in Picsel, in collaboration with the travel agency Degriftour.