Grids of Grids of Simple Services

We have of course discussed Grids extensively here in previous articles and we adopt the view that they represent the system formed by the distributed collections of electronic capabilities that are managed and coordinated to support some sort of enterprise (virtual organization). Sometimes one reserves Grid to describe just the technology used to build these electronic communities or organizations. One thinks of Grid technology as the CyberInfrastructure (NSF) or e-Infrastructure (European Union) that supports e-Science, e-Business or in fact e-moreorlessanyenterprise. There is no firm consensus as to the best Grid approach but we will adopt the popular architecture based on Web services. There is a vigorous debate in the community as to the “right” way to do this and if conventional Web services need enhancement to cope with the large scale secure managed distributed services needed in a Grid. In particular there is lot of debate on the appropriate ways to represent state and how much to standardize in this area. WSRF (Web Service Resource Framework http://www.globus.org/wsrf/) and WS-GAF (Web Service Grid application Framework http://www.neresc.ac.uk/ws-gaf/) are two important activities whose development and interaction will have important implications for the detailed structure of services. However here we discuss aspects independent of these issues – namely “what is the right size” for a service and how should one package services and Grids together. Often one considers Grids as providing seamless access to a set of resources; here we adopt this view with however an architecture with many “small Grids”. This reflects the many different types of overlapping communities and resource collections that naturally form individual Grids. Each individual Grid can have a seamless elegant environment – in fact this could be a criterion for defining Grids – but a composite Grid would amalgamate multiple such subGrids and exhibit a resultant heterogeneous environment. In other words, we do not expect there to be a few Grids produced but very many that can get composed, divided and overlapped together to support dynamic communities and requirements.