The management of data within Grids is a challenging problem. It requires providing easy access to distributed, heterogeneous data that may reside in different ‘administrative domains’ and may be represented by heterogeneous data formats, and/or have different semantic meaning. Since applications may access data from a variety of storage repositories, for example, file systems, database systems, Web sites, document management systems, scientific databases, and so on, there is a need to define a hig