In a distributed system such as a Data Grid, it is desirable to maintain and query dynamic and timely information about active participants such as services, resources and user communities. This enables information discovery and collective collaborative functionality that operate on the system as a whole, rather than on a given part of it. However, it is not obvious how a database (registry) should maintain information populated from a large variety of unreliable, frequently changing, autonomous and heterogeneous remote data sources. In particular, how can one avoid sacrificing reliability, predictability and simplicity while allowing to express powerful queries over time-sensitive dynamic information? We propose the so-called hyper registry, which has a number of key properties. An XML data model allows for structured and semi-structured data, which is important for integration of heterogeneous content. The XQuery language allows for powerful searching, which is critical for non-trivial applications. Database state maintenance is based on soft state, which enables reliable, predictable and simple content integration from a large number of autonomous distributed content providers. Content link, content cache and a hybrid pull/push communication model allow for a wide range of dynamic content freshness policies, which may be driven by all three system components: content provider, hyper registry and client.
Special Issue Papers