In June 2003, the Global Grid Forum (GGF) adopted the Open Grid Services Infrastructure (OGSI) specification as a GGF standard. OGSI is essential to the Open Grid Computing vision as it is the foundation on top of which the building blocks of future Grid applications will be placed. Those building blocks, the Grid services, are being defined by various GGF working groups, with the Open Grid Services Architecture (OGSA) working group orchestrating the entire process.
This article introduces OGSA, presents the OGSI specification, and discusses the significant role of Web service standards in Grid computing.
Grid Computing
Grid computing has been a hot topic in the news recently. Major vendors like IBM, HP, and Sun have not only been advertising their plans to support Grid computing, but they have also started rolling out their first e-business and e-science solutions.
All the interest in Grid computing led to the formation of the Global Grid Forum (GGF; www.ggf.org), a forum for the discussion of Grid-related ideas and the promotion of enabling technologies. One of its main activities is the creation of a standards-based platform for Grid computing with emphasis on interoperability.
But, what is the Grid? And, what does the term "Grid computing" mean? It could be about virtual organizations, or the integration of distributed resources, or a universal computer, or even about interconnecting supercomputers depending on who you talk to. A definition of the Grid is beyond the scope of this article. Your favorite Web search engine will provide you with many links to definitions and information. There are also a number of books out there from which you can draw information.
OGSA
The blueprint of the Grid architecture is defined by OGSA (www.ggf.org/ogsa-wg) as a set of fundamental services whose interfaces, semantics, and interactions are standardized by the GGF working groups. OGSA plays the coordinating role for the efforts of these groups. It identifies the requirements for e-business and e-science applications in a Grid environment and specifies the core set of services and their functionality that will be necessary for such applications to be built, while the technical details are left to the groups.
While OGSA has adopted a services-oriented approach to defining the Grid architecture, it says nothing about the technologies used to implement the required services and their specific characteristics. That is the task of OGSI.
Figure 1 shows the relationship between OGSA, OGSI, and the Web services standards. Also, a list, which is not exhaustive, of candidate core services is presented. It is expected that in the months to follow, OGSA will standardize this list.
OGSI
The OGSI working group decided to build the Grid infrastructure on top of Web services standards, hence leveraging the great effort - in terms of tools and support-that the industry has put into the field. Nevertheless, the group identified some key characteristics missing from Web services standards that they thought would be instrumental in building Grid applications, including the ability to create new services on demand (the Factory pattern); service lifetime management; statefulness; access to state; notification; and service groups.
