Developing a WSRF-compliant grid resource-broker service

The sharing of various kinds of distributed resources in heterogeneous and dynamically changing environments represents the core functionality of any grid system. The resources are shared among users with various levels of intertrust-relations, and belonging to different administrative domains with different security policies. The sharing is achieved through software modules called resource brokers that hide the complexity of grids by automatic submission of the user's jobs to most suitable grid resources. The functionalities of resource brokers include transformation of user requirements into a set of grid jobs, examination of grid resources and their capabilities, matching of job requests and their requirements against the resources, scheduling of jobs on the appropriate resources, initiation and monitoring the execution of jobs and collection of results when they are finished. In this paper, the development of a resource-broker service implemented under the DataMiningGrid [1] project will be presented. The project represents a large-scale effort aimed at developing a generic system facilitating the development and deployment of grid-enabled data mining applications. The project developed a grid middleware that supports execution of data mining tasks while utilizing data and computational resources of the grid. As a part of this middleware, a resource-broker service that takes into account special requirements of the data mining applications was designed and implemented. One of the key requirements for the developed service was compliance with the existing grid standards. Standardization of the implementation technologies as well as the core grid functionalities are important for allowing interoperability among different grid components. Today, the Open Grid Services Architecture (OGSA) [2] specifications, which were published by the Open Grid Forum (OGF) [3], represent the most mature standards in the area of grid computing. OGSA aims to standardize practically all the services one commonly finds in a grid system by specifying a set of standard interfaces for these services. Furthermore OGSA defines extensions of the common web services technologies and in this way acts as a standard middleware between grid applications and low-level web services technologies [Figure 1]. Extensions of the basic web services specifications are needed since they do not provide a standard way of modeling and management of the service state. Guided by the principle of interoperation through conformance specification, OGSA therefore proposes a set of specifications known as OGSA WSRF Basic Profile 1.0 [4] that consists of a set of de facto, institutional or evolving web services specifications, along with clarifications, refinements, interpretations and amplifications of those specifications that promote interoperability among implementations of the basic profile. The profile includes specifications of interfaces and behavior defined in WSRF, WS-Addressing and WS-Notification families of specifications. Globus Toolkit Version 4 (GT4) [5] represents a de-facto standard for developing grid applications. It includes quite a few high-level services that can be used to build grid applications, along with the service development and service execution environment. GT4 provides implementations of WSRF specifications for the programming languages Java, C and Phyton. The GT4 toolkit and Java WSRF implementation (Java WS Core) were used in implementation of the WSRF-compliant resource-broker service presented in this paper.