There exist two principally different approaches to the organization of problem solving in VO: 1) information resources driven approach; 2) scientific problem driven approach. Intrinsic difficulties of the first approach: semantic gap between resources and the problem, instability of global schema w.r.t. a set of resources, inability of automatic identification of resources for the problem. To implement the second approach a mediation technology is required. Advantages of the mediator approach include truly semantic integration of heterogeneous resources due to their semantic mapping into the mediator; multiple subjects can be semantically integrated applying recursive structure of the mediators.
Basic methods supporting the mediation technology include: 1) identification of relevant resources by metadata, ontologies, information structure, behaviour while registering in mediator resource classes in terms of the mediator classes; 2) rewriting queries (rules) expressed in terms of a mediator into rules over relevant data and services; 3) running workflows with rules as tasks over distributed heterogeneous resources. The mediator tool prototypes for these methods are planned at the end of 2006.
In May 2005 the RVO information infrastructure (RVOII) project report has been published (joint effort of SAO RAS, INASAN, IPI RAS). A structural design of RVOII has been developed. Basic principles of RVOII are defined as: representing infrastructure as a network of interoperating web (Grid) services, moving processing to data, encouraging code reuse and composition in SOA, emphasizing subject mediators to support various subject domains in astronomy. A Community centre in Moscow for support of scientific astronomical problem solving over distributed repositories of astronomical information has been created. First experience shows that usage of AstroGrid as the RVOII core is suitable according to the RVOII principles. Analysis of possibility of synergy of AstroGrid and mediation infrastructures has been undertaken. Respective prototype is planned in 2007.