Definition:
Open Grid Services Architecture (OGSA) is a set of standards that extends Web services and service-oriented architecture to the grid computing environment. OGSA definitions and criteria describe how information is shared and distributed among the components of large, heterogeneous grid systems; they apply to hardware, platforms and software.
Grid computing has intrigued the IT world for years. The notion of harnessing the processing power of multiple computers whether within an organization, supplied by volunteers or provided as a broadband, metered computing utility is attractive and compelling, but implementing it has proved somewhat difficult. One of the more recent developments advancing this cause, OGSA extends the idea of Web services to the universe of grid computing and thereby extends and refines the concept of service-oriented architecture.
To create workable grid services, developers have had to address several important issues: how to establish identity and negotiate authentication, how to express and negotiate policy, how to find out what services are available, how to negotiate and monitor service-level agreements, how to organize and manage collections of services to deliver reliable and scalable services, and how to integrate data resources into computations.
OGSA is based primarily on the technologies of Web Service Description Language (WSDL) and Simple Object Access Protocol (SOAP), an XML-based protocol for passing messages between systems over the Internet. It is service- oriented because it works as a series of loosely coupled, interacting services that use industry-accepted Web services standards.
For a Web service to be considered a grid service, clients must be able to easily discover, update, modify and delete information about the service and its functionality and relevant data; define how the service evolves; and ensure ongoing compatibility with other services.
Origins
OGSA began with work in the late 1990s at Argonne National Laboratory, IBM, the University of Chicago and other institutions. Today, OGSA development activities are under the direction of the Open Grid Forum (www.ogf.org). This community, representing more than 400 organizations worldwide, was formed by the 2006 merger of the Global Grid Forum and the Enterprise Grid Alliance.
What OGSA Does
OGSA builds on concepts and technologies from both the grid and Web services communities, defining a uniform vocabulary and grammar for grid services. OGSA represents almost everything you can do as an instance of a grid service that is, a transient Web service that can be located within the grid and combined dynamically with other services to form larger systems and applications. The transience is what makes a grid service different from a Web service. Transience means the services can be activated and deactivated in a timely manner without destroying the data required for many operations.
Mechanisms
Using WSDL, OGSA defines a number of mechanisms required for creating and composing distributed applications from available grid services:
- Underlying services, originally called Open Grid Services Infrastructure (OGSI), were intended to form the basic plumbing layer for OGSA. This has since been superseded by Web Service Resource Framework, a family of standardized specifications for Web services, and WS-Management, a SOAP-based protocol specification for the management of servers, devices and applications.
- Execution management services can create specific units of work and manage them to completion. These units can be OGSA applications or legacy applications.
- Data services move, access and update data resources, such as files, streams, databases and catalogs.
- Resource management handles data resources, other resources on the grid and the OGSA infrastructure.
- Security for authentication, identity mapping, authorization, credential conversion, auditing, secure logging and privacy.
- Self-management of services include the ability of a system to configure and repair itself and optimize mechanisms for resources.
- Information services can be named, discovered, logged, monitored and notified.
Kay is a Computerworld contributing writer in Worcester, Mass. You can contact him at russkay@charter.net.