Stavros Papastavrou

Mobile agents for World Wide Web distributed database access

The popularity of the Web as a universal access mechanism for network information has created the need for developing Web-based DBMS client/server applications. However, the current commercial applet-based approaches for accessing database systems offer limited flexibility, scalability, and robustness. We propose a new framework for Web-based distributed access to database systems based on Java-based mobile agents. The framework supports lightweight, portable, and autonomous clients as well as operation on slow or expensive networks. The implementation of the framework using the aglet workbench shows that its performance is comparable to, and in some case outperforms, the current approach. In fact, in wireless and dial-up environments and for average size transactions, a client/agent/server adaptation of the framework provides a performance improvement of approximately a factor of ten. For the fixed network, the gains are about 40 percent and 30 percent, respectively. We expect our framework to perform even better when deployed using different implementation platforms as indicated by our preliminary results from an implementation based on Voyager.

Mobile agents for WWW distributed database access

The popularity of the Web as a universal access mechanism for network information has created the need for developing Web based DBMS client/server applications. However, the current commercial applet based methodologies for accessing database systems offer limited flexibility, scalability and robustness. We propose a new framework for Web based distributed access to database systems based on Java based mobile agents. The framework supports lightweight, portable and autonomous clients as well as operation on slow or expensive networks. The implementation of the framework shows that its performance is comparable to, and in some cases outperforms, the current approach. In fact, in wireless and dial-up environments and for average size transactions, a client/agent/server adaptation of the framework provides a performance improvement of approximately a factor of ten. For the fixed network, the gains are about 40% and 30% respectively.

A decade of dynamic web content: a structured survey on past and present practices and future trends

The shift from static to dynamic Web content has been dramatic. Dynamic Web content is facilitated by specialized cooperating component systems better known as content middlewares. Unlike static content, the generation and delivery of dynamic Web content introduce heavy a workload on content middlewares. To address this problem, numerous research approaches have been proposed in the literature, some of which are the driving force behind popular commercial systems, a fact that stresses the importance and applicability of this research area. This article surveys the literature during the period of 1995‐2005 on accelerating the generation and delivery of dynamic Web content. It classifies the proposed approaches into taxonomies based on their underlying methodologies and practices. In order to illustrate the evolution of research, we introduce a research-charting semi-formal framework called the Caching Fragmentation Polymorphism (CFP) framework, within which we relate the surveyed approaches and depict their relationships.

UCYMICRA: Distributed Indexing of the Web Using Migrating Crawlers

Due to the tremendous increase rate and the high change frequency of Web documents, maintaining an up-to-date index for searching purposes (search engines) is becoming a challenge. The traditional crawling methods are no longer able to catch up with the constantly updating and growing Web. Realizing the problem, in this paper we suggest an alternative distributed crawling method with the use of mobile agents. Our goal is a scalable crawling scheme that minimizes network utilization, keeps up with document changes, employs time realization, and is easily upgradeable.

AN EVALUATION OF THE JAVA-BASED APPROACHES TO WEB DATABASE ACCESS

Given the undeniable popularity of the Web, providing efficient and secure access to remote databases using a Web browser is crucial for the emerging cooperative information systems and applications. In this paper, we evaluate all currently available Java-based approaches that support persistent connections between Web clients and database servers. These approaches include Java applets, Java Sockets, Servlets, Remote Method Invocation, CORBA, and mobile agents technology. Our comparison is along the dimensions of performance and programmability. Our findings point out that best performance is not always achievable with high programmability and low resource requirements. Moreover, the mobile agent technology needs to improve its programmability while giving particular emphasis on its infrastructure.

Performance vs. freshness in web database applications

In this work, we present a novel approach for the efficient materialization of dynamic web pages in e-commerce applications such as an online retail store with millions of items, hundreds of HTTP requests per second and tens of dynamic web page types. In such applications, user satisfaction, as measured in terms of response time (QoS) and content freshness (QoD), determines their success especially under heavy workload. The novelty of our materialization approach over existing ones is that, it considers the data dependencies between content fragments of a dynamic web page. We introduce two new semantic-based data freshness metrics that capture the content dependencies and propose two materialization algorithms that balance QoS and QoD. In our evaluation, we use a real-world experimental system that resembles an online bookstore and show that our approach outperforms existing QoS-QoD balancing approaches in terms of server-side response time (throughput), data freshness and scalability.

Fine-Grained Parallelism in Dynamic Web Content Generation: The Parse and Dispatch Approach

Dynamic Web content is gaining in popularity over traditional static HTML as the means of providing Web users with personalized and dynamic information. To enable dynamic content, various technologies have been developed for embedding of script code blocks into static HTML files in order to perform various forms of tasks such as session tracking, bank transactions, financial calculations, products catalog generation, dynamic image generation, or even fetching information from remote servers. In this way, static HTML pages are transformed into dynamic web pages. Typically, dynamic Web pages include a number of tasks that are executed in a serial manner by current Web servers. In this paper, we propose a back-end, finer-grained parallel approach for dynamic content generation, and elaborate on how it affects the design and performance of Web servers. We have developed a prototype Web server that supports the parallel processing of tasks involved in the dynamic content generation with improved throughput as compared to the serial approach.

An Evaluation of the Java-Based Approaches to Web Database Access

Given the undeniable popularity of the Web, providing efficient and secure access to remote databases using a Web browser is crucial for the emerging cooperative information systems and applications. In this paper, we evaluate all currently available Java-based approaches that support persistent connections between Web clients and database servers. These approaches include Java applets, Java Sockets, Servlets, Remote Method Invocation, CORBA, and mobile agents technology. Our comparison is along the dimensions of performance and programmability.

Exploring content dependencies to better balance performance and freshness in web database applications

In this paper, we present a novel approach for materializing dynamic web pages by exploiting content dependencies and user access patterns. We introduce two new semantic-based data freshness metrics and show that our approach out-performs traditional balancing QoS-QoD approaches in terms of server throughput, increased data freshness and scalability. In our evaluation we use a real-world experimental system that resembles an online bookstore web database application.

A survey on the Java-based approaches for Web database connectivity

The popularity of the Web makes the efficient access of distributed databases from Web clients an important topic. Various methods for Web database integration have been proposed but there is an increasing interest on those based on Java. This is due to the Inherent advantages of Java, which supports platform independence and secure program execution, and produces a small size of compiled code. In this experimental paper, we evaluate all currently available Java-based approaches. These include Java applets, Java Sockets, Servlets, remote method invocation, CORBA, and mobile agents. To this end, we implemented a Web client accessing a remote database using each of these approaches and compared their behavior along the following important parameters: (1) peformance expressed in terms of response time under different loads, (2) transparency of communication expressed in terms of complexity of networking API, and (3) extensibility expressed in terms of ease of adding new components.