GRID ARCHITECTURE THE BASE FOR VIRTUAL ENVIRONMENT S DESIGN

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1 GRID ARCHITECTURE THE BASE FOR VIRTUAL ENVIRONMENT S DESIGN Todor Stoilov, Elena Ivanova Institute of Computer and Communication Systems, Bulgarian Academy of Sciences, Phone: , Е-mail: todor@hsi.iccs.bas.bg e_ivanova@hsh.iccs.bas.bg Bulgaria Abstract: Integration of informational resources in common virtual environment is considered. Virtual collaborative environments aim to join research efforts in emerging applications of the GRID technologies. Wide range of GRID services can be developed as Web services. The general components in the integration are described. The main steps in developing virtual environments are outlined. Architecture of an integrated environment is presented. Introduction GRID technology is becoming more and more applicable in the area of distributed computing. This is because GRID computing provides the best framework for exploring new ideas in collaborative virtual environments and advanced interfaces to high-performance computing systems. It also provides an ideal focus for studying advanced networking concepts and related human performance issues. The GRID infrastructure can facilitate many applications including data exploration and integration, collaborative engineering, and service-oriented computing. GRID computing can be considered as a method for integrating a variety of systems connected together in the large network. The main advantage of GRID is that it can aggregate the computing power of computers distributed over many institutions at different cities or countries. The conceptual scheme of a general GRID can be presented by three-layer model [1], as it is shown on fig.1. The fist is physical layer comprising the actual aggregation of computational resources such as storage systems, data and meta-data, multimedia or input and output devices. The second is an abstract virtual layer, which hides the physical interconnections between the resources. It is a user s view for the GRID as a virtual supercomputer. And the third is the user layer, providing user-friendly interfaces. Web services allow GRIDs to be specified as services that can interoperate with each other. Wide range of GRID services, particularly those focused on information services (queries) and on control can be developed as Web services. Web services are new phenomenon in the computer industry. They provide standard means of interoperating between different software applications, running on a variety of platforms and/or frameworks. The Web service refers to a service over a computer network that resides in a specific environment. The environment provides means to describe and to discover the services, interact with other services to provide integration of functionalities. The Web service as a programmable application logic is accessible using standard Internet protocols. Web services combine the best aspects of component-based development and the web. Like components, Web services represent functionalities that can be easily reused without knowing how the service is implemented. Practically Web Services have emerged as a powerful mechanism for integrating information resources. The Web services paradigm takes all the best features of the Service-Oriented Architecture (SOA) and combines it with the Web. The Web supports universal communication, using loosely coupled connections. The resulting technology eliminates the usual constraint of DCOM, CORBA or RMI. Thus the Web services support web-based access, easy integration and service reusability.

2 User Level Virtual Level Physical Level Fig.1: Conceptual scheme of a GRID three-layer model State-of-the-art in GRID Computing and Web Services Currently the research GRID projects aim to deliver test GRID infrastructures providing proofs of concept and opening opportunities for new ideas, developments and further research. Examples are the Condor Project, CrossGrid, the EU DataGrid, the Globus Project, GridLab, Legion, NorduGrid, Unicore, Javelin and many more. The software developed in such projects generally lacks interoperability among different solutions. Only recently there has been an effort to agree on a unified Open GRID Service Infrastructure (OGSI) [2]. OGSI proposes a standard to enable GRID middleware, which has been developed by any of the projects, to interoperate. Earth System GRID II [3], is such an effort, involving the development of a virtual collaborative environment. ESG II has a potential for a very significant improvement of scientific productivity, collaboration and of knowledge exchange among climatologists. Pervasive Collaborative Computing Environment [4] allows participants to locate each other, use asynchronous and synchronous messaging, share documents, share progress, share applications and hold videoconferences. The definition of a service given according to [5] is a service is an active program or software components in a given environment that provides and manages access to a resource that is essential for the function of other entities in the environment. Now the Web services are located and published in the web as program applications. The last are invoked across the Web from customers by means to integrate the application result set for the customer service [6]. The services can perform functions

3 ranging from simple requests to complicated business processes. Once a web service is deployed, other applications and services can discover and invoke the deployed service. Nowadays Web services are an effort to build a distributed computing platform for the web and address three general questions: What goes on the wire, which concern the formats and protocols, used for the web service implementation; What describes what goes on the wire? This answer concerns the manner of description of the web services. What allows the consumer to find the service description? This concerns the technology of discovering the services. These three general pillars of the web service deployment have its development and achievements. The Web service framework is being defined, standardized and supported by the industry at a record pace. It receives broad industry acceptance and standard compliance, which makes it widely applicable [7-11]. Thus a very high level of interoperability of the Web applications is achieved. Technologies Virtual environment s design involves in combining multiple innovative technologies. Web services, developed by World-Wide Web consortium (W3C), are the main standards for information interchange and remote access to software and applications as a service. The XML formats of data presentation are assumed as natural extension of the HTML coding [12]. Due to its inner free tag definition structure, XML technology is widely applied in the Web for data presentation and data serialization. The communication and messaging between XML results sets is performed by the protocol SOAP. SOAP (Simple Object Access Protocol) is a lightweight, XML-based messaging protocol that contains an envelope, header, and body, designed to exchange information in a decentralized, distributed environment [13]. It is the channel used for communication between a Web Services provider application and a client application. The networked Web services are described by WSDL language [13]. WSDL (Web Services Definition Language) is an XML-based language, used to describe Web Services. A WSDL document describes the functionality of proposed Web Service, how it communicates and where it is accessible. The UDDI standard is developed to design a structured public registry consisting information about the info services and their functionalities. UDDI (Universal Description, Discovery, and Integration) is an XML-based Web Services standard [13]. Service Oriented GRID Architecture A virtual environment, consisting of heterogeneous components, is based on distributed Service- Oriented Architecture. SOA is architecture consisted of components and interconnections that stress interoperability and location transparency [14]. In fact, SOA is a collection of services, but any service has to be equipped with a suitable interface, which provides invoking over the network. The main parts of SOA are [14]: uniform data representation and exchange mechanism; standard way for communication; standard meta language to describe the services offered; mechanism to register and locate Web Services-based applications (fig.2).

4 The next figure represents SOA and mapping between the parts of SOA and Web Services technologies. WS description, using meta language Directory Services UDDI Uniform data representation and exchange - XML Standard communication channel - SOAP WS Provider WS Client Fig.2. Service Oriented Architecture Main Stages in developing Virtual Environments The following main steps towards developing virtual environment can be outlined, considering the architecture discussing above(fig.3): Requirements Analysis & System specifications - analyzing the requirements and the specifications of all approaches for the use of Web services and GRID enabled technologies for virtual collaboration environments. Functional architecture - defining the ideal target functional architecture for the virtual collaboration environment with possible intermediate architectures. Service modelling - investigating, classifying and specifying a set of service building blocks for the virtual environment. Service Implementation - the implementation processes for the target set of building blocks that have been defined in the previous step. Integration of the various modules - the integration of the various modules developed in the GRID infrastructure. Evaluation - evaluation of the developed system Exploitation putting the system into action. Implementation of GRID services system Description of an integrated system for retrieving information, accessible through different devices computers or mobile phones is provided. The main goal of the application is to provide services for selective search in a database, accessible through traditional WEB and through WAP (Wireless Application Protocol). The relational database is distributed - the tables of the database are stored on

5 two machines and are managed from different database servers, i.e. the database is heterogeneous. The client of the application, which is WEB browser or WAP browser, obtains selective search from the database by user-entered keywords. Requirements Analysis & System specifications Functional architecture Service modelling Service Implementation Integration of the various modules Evaluation Exploitation Fig.3. Main Stages in developing Virtual Environments The information system is built in four logical hierarchical levels as it shown on figure 4. For the first level the client is used WEB or WAP browser. In this part of the application the communication is through HTTP or WAP protocols. The second level is implemented by several WEB servers one is the main which serves the WEB site or the WAP site, and the others are on the machines that house the database. In order to avoid license limitations the several open source products are used: Apache WEB server [15], PHP server side scripting language [16]. The connection with the next level is NuSOAP, an open source SOAP implementation, deployed with PHP scripting language by Nusphere corp [17]. It is a middle level between the second and the third level. This library is used without any changes. The third level can be considered as the Web Service interface of the application. It consists of two main parts. In the part of the main server third level comprises WSDL client, WSDL document and service-application-file. The WSDL client connects to the WSDL document and thus sends requests to the searching functions. On the part of the remote machines the level includes modules, named SOAPServer, for connection with the relevant database servers. These modules communicate through SOAP protocol, i.e. SOAP is used as an approach for communicating between the machines on which

6 the database s tables are stored. The fourth level is the database level. MySQL database [18] is used because of avoiding license limitations again. Ι level Client Ι Ι level Apache PHP Apache PHP Apache PHP NuSOAP NuSOAP NuSOAP Ι Ι Ι level SOAP Server SOAP/WSD L Client SOAP Server WSDL Service Ι V level Database 1 Database 2 Fig. 4. Four level architecture of the system. Conclusion The concept of GRID computing is powerful. It provides the ideal framework for developing virtual collaborative environments. Web services allow GRIDs to be specified as integrated services that can interoperate with each other. Thus variety information resources are put together into a virtual supercomputing system. The main components in the integration were described as well as the main steps in developing virtual environments. The integrated system for multiple search in databases, based on Service Oriented GRID Architecture and Web Service was presented.

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