|Author(s): || Briukhov D., Kalinichenko L., Martynov D., Skvortsov N., Stupnikov S., Vovchenko A., Zakharov V., Zhelenkova O.
| The report considers the middleware architecture of subject mediators in the hybrid grid-infrastructure for scientific problem solving over a set of heterogeneous distributed information resources (such as databases, services, ontologies) integrated by the mediators. The infrastructure is hybrid because it is constructed as a binding of the AstroGid Virtual Observatory system developed in the UK and of the middleware supporting subject mediators developed at the Institute of Informatics Problems of RAS. In the mediator middleware an approach driven by applications is used. According to this approach for a class of applications a specification of subject domain (a mediator) is formed independently of the pre-existing information resources. Another approach of the information integration driven by resources forms a specification of a mediator as a composition of pre-selected resource schemas. The main deficiency of this approach is that any modification of a set of selected resources leads to change the specification of the mediator schema. The application-driven mediation middleware provides the following basic functions: a) specification of a mediator as a result of consolidation effort of community related to the respective application domain; b) semantic identification, mapping and registration of relevant resources in the mediator supported by the Information Resource Registration tool of the middleware; c) mappings of information models (description languages) of heterogeneous information resources into the canonical model of the middleware supported by the Information Model Unifier tool.
Integrated access to the resources registered at the mediator is provided by the Executive Engine of the mediation environment applying the mediator query (program) rewriting system. An example of implementation in the hybrid grid-architecture of a subject mediator for solving of distant radio galaxies discovery problem is presented in (http://synthesis.ipi.ac.ru/synthesis/projects/Z_DGS/). The paper  shows how in the mediator architecture the complicated problems of semantic integration of information resources and of queries rewriting into the plans of their implementation over registered resources are solved. The distinguishing features of the presented approach comparing to the well known prototypes of database integration are overviewed. The middleware architecture of subject mediators is planned to be used for solving the Russian Virtual Observatory problems.
 Briukhov D.O., Vovchenko A. E., Zakharov V.N., Zhelenkova O.P., Kalinichenko L.A., Martynov D.O., Skvortsov N.A., Stupnikov S.A. The Middleware Architecture of the Subject Mediators for Problem Solving over a Set of Integrated Heterogeneous Distributed Information Resources in the Hybrid Grid-Infrastucture of Virtual Observatories Informatics and Applications, 2008, V. 2, Issue 1, p. 2-34 (In Russian).