| In this chapter, we explore a sample Globus GT3 implementation. This sample will introduce the concepts we have discussed in the previous two chapters, in terms of a Grid Computing implementation. In order to better understand this, familiarity with the basic concepts of Web services is a must. This includes understanding the concepts of the basic structure of SOAP messages, the JAX-RPC programming model, [1] and Apache AXIS runtime. [2] This sample discussion will discuss most of the programming aspects of grid services, which we can also find in the Globus GT3 toolkit. Should one desire to implement this sample as we are describing it, we are assuming that GT3 is correctly installed on the development machine (e.g., http://localhost:9080) [3] as a Web application with a root name of "ogsa." Before we begin working, we have to ensure that GT3 samples are properly working in the machine. This is because we are not including any service deployment and installation information in this chapter. Our intension is to introduce the concepts of GT3, from the point of view of the service developers and clients . This is a sample that is intended to be simple in nature. The sample is that of a search engine implemented as multiple grid services. Figure 13.1 shows this sample. Figure 13.1. The Acme Search Engine service utilized as the sample in this chapter.  It is important to understand that, although simple, this is a real functional sample; however, this sample is very primitive for purposes of understanding. This is, however, a powerful and extensible sample service implementation to explain the programming details on GT3. One may want to think about extending this sample to a real search engine, or delegate this to an existing search engine. The UML diagram in Figure 13.2 shows the interface hierarchy of this service implementation. Figure 13.2. UML diagram showing the Acme portTypes and service implementation.  This sample will be developed in a step-by-step fashion by adding functionalities one by one. The approach taken is a top-down approach, where we will start with a GWSDL description of the service to be implemented. | 