Balázs Goldschmidt

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 Mobile Agent-Based Infrastructure for an Adaptive Multimedia Server

This paper introduces a mobile agent-based infrastructure for an adaptive multi-media server enabling a dynamic migration or replication of certain multimedia applications among a set of available server nodes. It discusses the requirements from both, the server’s and the middleware’s point of view to each other and comes up with a specification and implementation of a CORBA-based interface between them.

Placement of nodes in an adaptive distributed multimedia server

Multimedia services typically need not only huge resources but also a fairly stable level of Quality of Services. This requires server architectures that enable continuous adaptation. The Adaptive Distributed Multimedia Server (ADMS) of the University Klagenfurt is able to dynamically add and remove nodes to the actual configuration, thus realizing the offensive adaptation approach.

A Metamodel for the Web Services Standards

Web services provide distributed communication in a platform independent way. The WS-* standards define how middleware aspects (security, reliability, transactions, etc.) can be realized through web services. Although the WS-Policy standard family can be used to configure the various WS-* protocols, they are very hard to construct and to maintain manually. In addition, most SOA products and Grid systems implementing these standards provide their own methods for configuring these protocols, making it very difficult to match the various configuration options of different products. This fact inspired us to propose a platform independent metamodel for describing distributed systems of web services including the most important WS-* standards. The present article defines the full metamodel, it specifies the corresponding programming language formally, and it shows the productivity of the framework built around the metamodel through real-life examples. The framework is capable of generating product specific configuration files and source codes, resulting in directly interoperable applications even between different SOA products. The framework could also promote interoperability with Grid systems built on WS-* protocols.

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.

A Performance Model for the Web Service Protocol Stacks

Web services are built on XML. They use XML for describing the service interface, they use XML for message exchange and the WS-* protocols that provide addressing, security and reliable messaging also use XML. This burdens the communication with a large response time overhead compared to binary distributed communications like CORBA or RMI. Therefore, it is important to know how to design the interface of a web service so we can minimize the communication overhead. In this paper we propose a performance model with which the response time overhead of web services with arbitrary interfaces can be predicted if the coefficients of the model are calculated from some simple measurements for the given set of test cases. The paper shows the measurement results for two web service frameworks and also gives a detailed description of the performance model.

Performance Analysis of Windows Azure Data Storage Options

Windows Azure provides an IaaS cloud service with virtual machines, web and worker roles and practically unlimited, pay-as-you-go storage options which can be used for applications requiring big data or parallel computing which is important in many fields including biology, astronomy, nuclear physics and economics.

Performance Analysis of Cloud-Based Application

Cloud computing, and IaaS cloud services in particular suit well to resource-intensive applications by offering on-demand allocation of computing power, storage space and network bandwidth together with pay-as-you-go billing system.