SPASE prototype : an example application for the interoperability in Space Physics

With the development of numerous independent data access systems across the world, a new need has recently appeared: the ability to query several systems simultaneously. This is interoperability, the ability to access multiple sites as if they were part of the local site. An international consortium, Space Physics Archive Search and Extract, is studying issues regarding interoperability for Space Physics. A prototype query system was developed two years ago, using XML technology. The concept is to implement interoperability between "participating data centers", via a unified interface. The use scenario then is: - The user defines a query. - The user's center contacts all other participating data centers, using a URL (and dictionaries to convert keywords). - Participating data centers each query their services(s) and generate a reply in XML in conformity with a given "results" DTD (Document Type Definition). - The user's center then parses all responses and produces a homogeneous presentation of the results. The present prototype implements basic, but important, search criteria: (1) Spacecraft, Instrument keywords; and, (2) Start/stop date and time. The result is a list of compliant data sets with a name, description (in HTML, with links to further information), and a URL to request each data set (or, at least, the data center relevant home page). This prototype uses a very simple protocol based on http and XML. It manages for each participating center a "resource description" which describes the services available (data set query, data granules query, ...), how (Protocol, Format, Parameter), and the format of the response. All descriptions are written in XML and are shared using http. The prototype will be presented with its probable evolution: the use of Web Services.