Introduction: AstroGrid increases scientific research possibilities by enabling access to distributed astronomical data and information resources. AstroGrid provides a standardized framework for astronomical data processing. Possibilities opened by AstroGrid to its users include publishing, co-operative analysis and visualization of data. AstroGrid framework is supported by a number of components bearing the following functionalities: Registry – Data discovery and resource directory, MySpace - The virtual data repository, CEA - Integrated applications for data manipulation, DataAccess – Access to the Data, Workflow - Tool to sequence applications working on a data set, and Auxiliary applications for portability of heterogeneous data. Registry Implementation Aspects. In the Virtual Observatory, the Registry serves a central warehouse of resource descriptors. However, the sources of this information and data providers are distributed. The distributed nature of the information used for resource discovery necessitates a common mechanism for registry and data interoperability. AstroGrid implements the International Virtual Observatory Alliance's ( agreed VOResource standard. By using the IVOA standard, the AstroGrid Registry can 'harvest' registry information from other VO projects, thus allowing astronomers access to resources located for example in the USA, Europe, or Japan. -Various resources used in the virtual observatory are described in XML. These resources include applications, data collections, generic services and web services. These services adhere to the AstroGrid CEA standard. This standard makes running of the services and applications possible. -Each resource available through AstroGrid is described by means of standard resource descriptors, implemented via a standard XML schema. -The AstroGrid registry is constructed using the eXist XML database as its backend which utilizes XQuery for the querying of the XML. EXist also gives the flexibility to store any kind of XML, including extensions to the IVOA standard resources from other virtual observatories. -AstroGrid Registry web services perform queries or search for data using ADQL. ADQL queries are subsequently translated into the XQuery language by the Registry web services. Resource Harvesting. Resources can be discovered and aggregated by means of the Registry. The Registry adheres to standard specifications and must have two interfaces: a search interface and a harvest interface. Harvesting is supported via the OAI for metadata harvesting defined as an HTTP GET interface. All registries have a standard interface implementing OAI – Open Archives Initiative. OAI promotes interoperability standards that facilitate dissemination of content. OAI enhances the availability of scholarly communication and content access. The OAI implemented by AstroGrid allows for both a web service and web browser version. The XML descriptor for a resource contains metadata on whether a resource requires a browser version or is called via a web service. 1. Mullard Space Science Laboratory, UCL, London, UK 2. Institute of Astronomy, Cambridge University, Cambridge, UK 3. CLRC/Rutherford Appleton Laboratory, Didcot, UK Myspace DataAccess CEA Community Workflow Portal Registry AstroGrid's implementation of the VO depends on resource discovery facility- the “Registry”. It operates on distributed heterogeneous information resources. Therefore multiple data sources need to interoperate through standard resource descriptors. AstroGrid is leading standardization of the distributed resource discovery by means of the Registry. Full Registry AstroGrid U.K. Full Registry NVO U.S.A Vizier Publish Registry France Specialized Local Registry MSSL, U.K. Types of Registries: IVOA has three types or definitions of Registries: Full Registry – This is the main Full Registry which supports the search and harvest interfaces and performs harvests of other Full and Publishing Registries. Publish Registry – A Registry that only supports the harvest interface by exposing its data through a web service or web browser supporting OAI for harvesting by Full Registries. Specialized Registry – Normally support only the search interface and are not harvestable. These registries are for more special purposes dedicated for a particular use. AstroGrid and the Registry: Enabling Resource Discovery Kevin Benson 1, Elizabeth Auden 1, Dave Morris 2, Brian McIlwrath 3