Zoltán László

Mobile agents in a distributed heterogeneous database system

The purpose of this paper is to present a new infrastructure for multimedia database searches based on CORBA and mobile agent technology. A new mobile agent system, called Vagabond, was implemented in pure Java using only standard CORBA facilities. The fundamental agent design and architecture is introduced. Measurements demonstrated the merits of Vagabond, namely the simple design, the implicit heterogeneity inherited from CORBA, and its speed. The system (renamed as M/sup 3/) was implanted inside an Oracle8i database system which is able to run Java code as a stored procedure. Further measurements have justified the idea presented above, ie. sending agents directly inside the database can decrease the response time of multimedia content search and retrieval. However, the required modifications made the embedded agency accessible for clients using only Aurora, Oracles modified Visi-broker ORB. On the basis of the Proxy design pattern, the paper presents a proxy solution that encapsulates the specific protocol issues that restricted interoperability, and thus provides the user of the infrastructure with the benefits of a truly heterogeneous environment.

Evaluation of WS-* Standards Based Interoperability of SOA Products for the Hungarian e-Government Infrastructure

The proposed architecture of the Hungarian e-Government Framework, mandating the functional co-operation of independent organizations, puts special emphasis on interoperability. WS-* standards have been created to reach uniformity and interoperability in the common middleware tasks for web services such as security, reliable messaging and transactions. These standards, however, while existing for some time, have implementations slightly different in quality. In order to assess implementations, thorough tests should be performed, and relevant test cases ought to be accepted. For selecting mature SOA products for e-Government application, a methodology of such an assessment is needed. We have defined a flexible and extensible test bed and a set of test cases for SOA products considering three aspects: compliance with standards, interoperability and development support.

A Proxy Placement Algorithm for the Adaptive Multimedia Server

Multimedia services are becoming widespread, while the network capacity can not keep up with the growth of user demands. Usually proxies are used to overcome the QoS degradation. One of the fundamental problems of applying proxies is to recognize the relevant set of proxy placement criteria, and to find a good algorithm. In this paper we propose a greedy algorithm variant, ams-greedy, that aims at taking into account the different property preferences of the proxy-server and the proxy-client links. We also analyse the consequences of the initial results.

Metaprogramming Library for the C# Programming Language

As software becomes more and more complex, tool-support for software analysis and transformation is increasingly important. While such tools exist for languages like Java, Smalltalk and C++, the support for C# is poor. In this paper we present Recoder.C#, a library for static metaprogramming of C# programs. Recoder.C# constructs a fully cross-referenced syntax tree and it supports transformation of this syntax tree. The Recoder parser is fully inversive, which means that the original code layout (comments, indentation) is preserved as far as possible. Recoder.C# can be used to build sophisticated analysis and transformation tools, including software metrics and refactorings.