5 Towards an integration of distributed data and information services

To go further, one needs to be able to integrate the result of queries provided by heterogeneous services. This is the aim of the ISAIA (Integrated System for Archival Information Access) project (Hanisch [2000a], [2000b]).

The key objective of the project is to develop an interdisciplinary data location and integration service for space sciences. Building upon existing data services and communications protocols, this service will allow users to transparently query a large variety of distributed heterogeneous Web-based resources (catalogs, data, computational resources, bibliographic references, etc.) from a single interface. The service will collect responses from various resources and integrate them in a seamless fashion for display and manipulation by the user.

Because the scope of ISAIA is intended to span the space sciences - astrophysics, planetary science, solar physics, and space physics - it is necessary to find a way to standardize the descriptions of data attributes that are needed in order to formulate queries. The ISAIA approach is based on the concept of profiles. Profiles map generic concepts and terms onto mission or dataset specific attributes. Users may make general queries across multiple disciplines by using the generic terms of the highest level profile, or make more specific queries within subdisciplines using terms from more detailed subprofiles.

The profiles play three critical and interconnected roles:

1.

They identify appropriate resources (catalogs, mission datasets, bibliographic databases): the resource profile;

2.

They enable generic queries to be mapped unambiguously onto resource-specific queries: the query profile;

3.

They enable query responses to be tagged by content type and integrated into a common presentation format: the response profile.

The resource, query, and response profiles are all aspects of a common database of resource attributes. Current plans call for these profiles to be expressed using XML (eXtensible Markup Language, an emerging standard which allows embedding of logical markup tags within a document) and to be maintained as a distributed database using the CDS GLU facility.

The profile concept is critical to a distributed data service where one cannot expect data providers to modify their internal systems or services to accommodate some externally imposed standard. The profiles act as a thin, lightweight interface between the distributed service and the existing specific services. Ideally the service-specific profile implementations are maintained in a fully distributed fashion, with each data or service provider running a GLU daemon in which that site's services are fully described and updated as necessary. Static services or services with insufficient staff resources to maintain a local GLU implementation can still be included, however, as long as their profiles are included elsewhere in the distributed resource database. The profile concept is not unique to space science, but would apply equally well to any distributed data service in which a common user interface is desired to locate information in related yet traditionally separate disciplines.