AstroGrid increases scientific research possibilities by enabling access to distributed astronomical

1
AstroGrid and the Registry Enabling Resource
Discovery
Kevin Benson1, Elizabeth Auden1, Dave Morris2,
Brian McIlwrath3

• 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.
Community
Portal
AstroGrid implements the International Virtual
Observatory Alliance's (http//www.ivoa.net)
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.
Registry
Myspace
Workflow
DataAccess
CEA
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.
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.  

• 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.

Full Registry AstroGrid U.K.
Full Registry NVO U.S.A
Specialized Local Registry MSSL, U.K.
Vizier Publish Registry France
1. Mullard Space Science Laboratory, UCL, London,
UK 2. Institute of Astronomy, Cambridge
University, Cambridge, UK 3. CLRC/Rutherford
Appleton Laboratory, Didcot, UK