During the past years, numerous Grid and Grid-like middleware products have emerged, to list some:
They are capable of providing (some of) the fundamental Grid services, such as Grid job submission and management, Grid data management and Grid information services. The emergence and broad deployment of the different middlewares brought up the problem of interoperability. Unfortunately, so far the Grid community did not meet the expectations of delivering widely accepted, usable and implemented standards. Nevertheless, some promising development has been started recently.
The NorduGrid Collaboration believes in coexistence of interoperable Grid middlewares and the diversity of Grid solutions. We don't think that a single Grid middleware is the solution neither we think it is achievable. NorduGrid strongly opposes any kind of monopolistic approach; instead we'd like to see well-defined, broadly accepted open interfaces of the various Grid middleware components. Interoperability should be achieved by establishing these interfaces based upon community standards. Interoperability is understood on the service level, on the level of fundamental Grid services and their interfaces.
Therefore NorduGrid intends to play an active role in several standardization processes and willing to invest efforts in the implementation and support of emerging standards. The Collaboration participates in the Rome CRM initiative, wants to contribute to the Glue-2.0 re-design, follows the GGF developments, cooperates with the major middleware development projects.
An interoperability snapshot of the NorduGrid/ARC middleware is presented below, organized by middleware components.
The security infrastructure of ARC fully complies with and relies on the Grid Security Infrastructure (GSI). GSI is a de facto community standard. Authorization within the different components currently uses the GACL framework and there are plans to support XACML systems too.
Currently ARC uses the extended Resource Specification Language (xRSL) for describing Grid job requests. The NorduGrid team, as a partner of the Rome CRM initiative, gradually moves towards the Global Grid Forum backed JSDL (see the comparison between the two languages).
ARC data management components support and are compatible with the most common solutions, such as the GridFTP protocol, storages based on traditional FTP and HTTP servers. ARC is also capable of interfacing to most commonly accepted open data indexing catalogues such as the Globus Replica Catalogue and the Globus RLS. There is a work launched to interface to the EGEE/gLite Fireman catalogue too. SRB systems are not supported due to the its restrictive license. ARC data management solutions will be compatible to the SRM standards.
A community-accepted information model and representation of Grid resources and entities is a cornerstone of interoperability. The major middlewares make use of different incompatible information models. ARC implements and relies on its own model, other large deployments make use of some alterations of the Glue model. The GGF is drafting a CIM-based model, which unfortunately seems to be lacking community support and acceptance. The current Glue model (version 1.2) was created by a small group and is known to be rather limited in some areas. A major re-design of Glue is expected to start in the 3rd quarter of 2005 and the NorduGrid Collaboration intends to be an active and significant player in that process
There is no standard job submission interface commonly accepted by the Grid community. In order to have a progress in the area, the Rome CRM initiative was launched in February this year. The NorduGrid Collaboration is committed to accept and implement the results of this working group. Current Grid systems make use of very different solutions for job submission: some of them rely on a particular GRAM implementation from Globus, others make use of Condor functionalities, or have their own proprietary protocol for that. The current NorduGrid/ARC implements job submission via GridFTP channel. It is foreseen that a standard job submission service will be implemented in a WS-RF framework. NorduGrid/ARC plans to redesign and reimplement its job submission system making use of WS-RF.
ARC collects usage information via the experimental ARC logger service. Each Grid job ran in the ARC system is described by a Usage Record. The current ARC Usage Record is rather preliminary, a radical re-design is planned. NorduGrid plans to use an extension of the GGF usage record which is unfortunately rather limited in its current form.