Scielo RSS <![CDATA[Journal of the Brazilian Computer Society]]> vol. 5 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Letter from the guest editors]]> <![CDATA[<B>Making Web Client Caching Cooperate at LAN Level</B>]]> Abstract In this paper, we investigate possibilities of making Web LAN-level client caching cooperate. The research was motivated by the fact that since LAN's usually have very high bandwidths, any communication within a LAN can be performed very efficiently. By adopting this caching scheme, much more client requests can be satisfied locally at very high speeds. Besides, external networks, servers and proxies will receive less burden. This work focuses on investigating its feasibility in the context of the Web and comparing the performance of several cooperative caching algorithms from different aspects: hit ratios, local proxy load, local network load and access latency. Performance of each individual client is also evaluated in terms of latency and machine load. <![CDATA[<B>Performance Analysis of WWW Cache Proxy Hierarchies</B>]]> Although caching and the creation of cache server hierarchies has became a popular strategy for reducing user waiting time and network traffic, there is no recipe for determining the best hierarchy configuration given a set of machines and the workload that they have to serve. This paper presents a novel approach for analyzing the performance of cache proxy hierarchies that is based on two metrics: hierarchical hit ratio and cache efficiency. This approach allows users to easily quantify trade-offs among configurations, facilitating the tuning of cache hierarchies. We illustrate our approach by analyzing possible configurations for a cache server hierarchy. <![CDATA[<B>Composite Nodes, Contextual Links and Graphical Structural Views on the WWW</B>]]> Recently, several open hypermedia systems (OHS) have proposed solutions for integrating with the World-Wide Web (WWW). The goal is to overcome WWW limitations using more powerful and sophisticated hypermedia data models while exploring the Web large distribution and standards, that permit interoperability and easy-of-use. This paper describes the integration of the HyperProp OHS with the WWW in a platform independent solution based on the Netscape browser. The integration allows: separation of links and presentation information from data content; definition of compositions (in order to structure documents, besides allowing the definition of contextual links and reuse of hypermedia structures); visualization of document structure; user navigation through graphical views; and navigation through guided tours and history trails. Particularly, the graphical views use filtering mechanisms based on extended fisheye view techniques, that avoid user disorientation when navigating through large documents. The integrated system also offers a web-site analysis tool. Based on the file system structure of web servers, the tool automatically generates compositions of HTML documents that, through the use of graphical views, help user navigation and information search on web-sites. <![CDATA[<B>Providing Context to Web Searches</B>: <B>The Use of Ontologies to Enhance Search Engine's Accuracy</B>]]> This paper presents the design and state of development of a framework for the construction and use of ontologies to guide searches in the Web or in document repositories. The aim is to enhance precision and recall in information retrieval sessions through the use of a context associated to each session. For transparency and flexibility, these contexts are dynamically built by the user from the system's available ontologies. This way, the user controls the conceptual structure underlying the search process, which should mirror his/hers information needs. Via the Ontologies Manager Framework, the user is able to access an incrementally built public ontology, as well as to create private ontologies, kept in the user's local area. Concepts to compose sessions' contexts can be selected from public and private ontologies. Private ontologies may be proposed by the user to integrate the public ontology, which is periodically upgraded by a maintenance module. This framework is a plug in which can be connected to a number of search engines. The initial experiments use Bright! (Brazilian Internet Guide in Hypertext) search engine as testbed. The prototype is implemented in Java, for portability and reusability. <![CDATA[<B>Signature Cache</B>: <B>A Light Weight Web Cache Indexing Structure</B>]]> Current trend in Web cache research is to have Web caches sharing their contents to improve the hit ratio. High performance Web cache sharing requires use of access indexes for Web caches to reference each other. The challenges facing the design of access indexes for Web cache sharing are the huge size, dynamic nature of Web cache contents, and high access speed. A recently proposed summary cache scheme [14] uses relatively small indexes for sharing Web caches to reference each other. We improved the summary cache scheme and propose a signature cache scheme. Instead of "repairing" existing access indexes, signature cache scheme builds new indexes to accommodate changes of Web cache contents. This scheme simplifies the maintenance of the indexes and significantly reduces the size of counters. Optionally, the size of the index can be further reduced by a semi-distributed index sharing mode at the cost of slightly increased response time. These improvements result in orders of magnitude reduction in the index size as compared to the summary cache scheme. <![CDATA[<B>Mirroring Resources in the World Wide Web</B>]]> One of the main problems faced by the users and service providers of the World Wide Web is that of a broken link in a hypertext, normally caused by the unavailability of a particular resource. The introduction of redundancy is the key mechanism to solve this problem. Unfortunately, the current infrastructure of the Web is based on a resource identification scheme that maps a resource identifier on a unique physical location; this scheme does not favour the implementation of a support for the replication of Web resources. In this paper we discuss how URNs (Uniform Resource Names), a resource identification scheme proposed by a special work group of the Internet Engineering Task Force (IETF), can be employed to implement a support for the mirroring of Web resources. Our proposal is based on the implementation of a proxy and a gateway that together allow conventional browsers and servers to access and manage mirrored resources transparently, allowing the provision of highly available Web resources