DIRAC (Distributed Infrastructure with Remote Agent Control) has been developed by the CERN LHCb physics experiment to facilitate large scale simulation and user analysis tasks spread across both grid and non-grid computing resources. It consists of a small set of distributed stateless Core Services, which are centrally managed, and Agents which are managed by each computing site. DIRAC utilizes concepts from existing distributed computing models to provide a lightweight, robust, and flexible system. This paper will discuss the architecture, performance, and implementation of the DIRAC system which has recently been used for an intensive physics simulation involving more than forty sites, 90 TB of data, and in excess of one thousand 1 GHz processor-years. Keywords grid computing, cluster computing, global computing, instant messaging, meta-scheduler, grid scheduling, batch system, job pull 1

Grids are collaborative distributed Internet systems characterized by large scale, heterogeneity, lack of central control, multiple autonomous administrative domains, unreliable components and frequent dynamic change. In such systems, it is desirable to maintain and query dynamic and timely information about active participants such as services, resources and user communities. The web services vision promises that programs are made more flexible, adaptive and powerful by querying Internet databases (registries) at runtime in order to discover information and network attached building blocks, enabling the assembly of distributed higher-level components. In support of this vision, we introduce the Web Service Discovery Architecture (WSDA), which subsumes an array of disparate concepts, interfaces and protocols under a single semi-transparent umbrella. WSDA specifies a small set of orthogonal multi-purpose communication primitives (building blocks) for discovery, covering service identification, service description retrieval, data publication as well as minimal and powerful query support. The individual primitives can be combined and plugged together by specific clients and services to yield a wide range of behaviors and emerging synergies. Based

An important aspect of service-centric systems (i.e. systems composed of services) is the ability to support service discovery at run-time in order to cope with unavailable or malfunctioning services. In this paper we present a framework that supports run-time service discovery. The central characteristic of this framework is the combination of components for monitoring the compliance of service-centric systems with requirements at run-time and components for discovering services at run-time. The framework uses the former components to detect violations of requirements at run-time and uses the specifications of the violated requirements to generate queries for discovering services that could substitute for malfunctioning services. It also uses queries derived from the process specification for service discovery. These queries incorporate both structural and behavioural aspects of the required services. 1.

Data Grids address the data intensive aspects of Grid computing, and therefore impose a very specific set of requirements on Grid Services. In this article the Data Grid problem is revisited with emphasis on Data Management. It investigates how Data Grid Services would need to be deployed within the Open Grid Services Architecture to fulfill the vision of the Data Grid. 1

In a large distributed system spanning many administrative domains such as a Grid, it is desirable to maintain and query dynamic and timely information about active participants such as services, resources and user communities. However, in such a database system, the set of information tuples in the universe is partitioned over multiple distributed nodes, for reasons including autonomy, scalability, availability, performance and security. This suggests the use of Peer-to-Peer (P2P) query technology.

In a large distributed system spanning many administrative domains such as a Data Grid, it is desirable to maintain and query dynamic and timely information about active participants such as services, resources and user communities. However, in such a database system, the set of information tuples in the universe is partitioned over many distributed nodes, for reasons including autonomy, scalability, availability, performance and security. It is not obvious how to enable general-purpose discovery query support and collective collaborative functionality that operate on the distributed system as a whole, rather than on a given part of it. Further, it is not obvious how to allow for search results that are fresh, allowing dynamic content. It appears that a Peer-to-Peer (P2P) database network may be well suited to support dynamic distributed database search, for example for service discovery. In this paper, we devise the Unified Peer-to-Peer Database Framework (UPDF), which allows to express specific applications for arbitrary query languages (e.g. XQuery, SQL) and node topologies, and a wide range of data types, query response modes (e.g. Routed, Direct and Referral Response), neighbor selection policies, pipelining characteristics, timeout and other scope options.

Service discovery has been recognised as an important aspect in the development of service centric systems, i.e., software systems which deploy web services. To develop such systems, it is necessary to identify services that can be combined in order to fulfill the functionality and achieve quality criteria of the system being developed. In this paper, we present a framework supporting architecture-driven service discovery (ASD) − that is the discovery of services that can provide functionalities and satisfy properties and constraints of systems as specified during the design phase of the development lifecycle based on detailed system design models. Our framework assumes an iterative design process and allows for the (re-)formulation of design models of service-centric systems based on the discovered services. The framework is composed of a query extractor, which derives queries from behavioural and structural UML design models of service centric systems, and a query execution engine that executes these queries against service registries based on graph matching techniques. The paper describes a prototype tool that we have developed to demonstrate and evaluate our framework and the results of a set of preliminary experiments that we have conducted to evaluate it.

Advents in network technology and distributed system design have propelled network communication service beyond best effort data delivery. With the rising complexity of network infrastructures and the need for on-demand provisioning operations, a high degree of self-sufficiency and automation is required in the network service infrastructure. Guided by the autonomic communication principle, this paper first presents an autonomic service provisioning framework for establishing QoS-assured end-to-end communication paths across administratively independent domains. Through graph abstraction, we show that the domain composition and adaptation problem could be reduced to the classic k-MCOP problem. In analyzing existing k-MCOP solutions, we show their inefficiencies when applied to the service provisioning context and establish a number of new domain composition and adaptation algorithms. These new algorithms are designed for the self-configuration, self-optimization and self-adaptation of end-to-end network communications and can provide hard QoS guarantees over domains with relative QoS differentiations. Through in-depth experimentations, we compare the performance of our algorithms with classic k-MCOP solutions and demonstrate the effectiveness of our approach.

Abstract. Global grid systems with potentially millions of services require a very effective and efficient service discovery/location mechanism. Current grid environments, due to their smaller size, rely mainly on centralised service directories. Large-scale systems need a decentralised service discovery system that operates reliably in a dynamic and error-prone environment. Work has been done in studying flat, decentralised discovery architectures. In this paper, we propose a hierarchical discovery architecture that provides a more scalable and efficient approach. We describe our design rationale for a k-ary tree-based fault-tolerant discovery architecture that also acts as an intelligent routing network for client requests. We show that it is possible to provide ad hoc multicast discovery of services even without end-to-end multicast availability. The system provides clients with the ability to search for services with incomplete information using descriptive service attributes. Our results demonstrate that this approach is well suited to wide-area discovery if fast discovery, high availability, scalability and good performance are crucial requirements. Key words. Grid, global computing, discovery, multicast, hierarchical overlay, service 1. Introduction. Service discovery is an essential component of global grid systems where the number of services can be in the order of millions. Services are dynamic; they may join or leave the system as they wish. Hardware or software components may fail at any time, services can be migrated to or service replicas can be launched at new locations. Consequently, without having an effective solution for locating suitable services in a wide-area environment, grids will not be usable.

In a large distributed system spanning many administrative domains such as a Grid, it is desirable to maintain and query dynamic and timely information about active participants such as services, resources and user communities. However, in such a database system, the set of information tuples in the universe is partitioned over one or more distributed nodes, for reasons including autonomy, scalability, availability, performance and security. This suggests the use of Peer-to-Peer (P2P) query technology. A variety of query response modes can be used to return matching query results from P2P nodes to an originator. Although from the functional perspective all response modes are equivalent, no mode is optimal under all circumstances. Which query response modes allow to express suitable trade-offs for a wide range of P2P applications? In this paper, we answer this question by systematically describing and characterizing four query response modes for the Unified Peer-to-Peer Database Framework (UPDF) proposed in our prior studies, namely Routed Response, with respect to distribution and location transparency, efficiency of query support, economics, number of TCP connections at originator and agent, latency, caching and trust delegation to unknown parties. We discuss to what extent a given P2P network must mandate the use of any particular response mode throughout the system. As a result, and shifts, in arbitrary permutations.