The Grid aims to support secure, flexible and coordinated resource sharing through providing a middleware platform for advanced distributing computing. Consequently, the Grid’s infrastructural machinery aims to allow collections of any kind of resources—computing, storage, data sets, digital libraries, scientific instruments, people, etc—to easily form Virtual Organisations (VOs) that cross organisational boundaries in order to work together to solve a problem. A Grid depends on understanding the available resources, their capabilities, how to assemble them and how to best exploit them. Thus Grid middleware and the Grid applications they support thrive on the metadata that describes resources in all their forms, the VOs, the policies that drive then and so on, together with the knowledge to apply that metadata intelligently

Corcho, Oscar

English

Archivo Digital UPM

An Ontology for Scientific Information in a Grid Environment:

Science and the Semantic Web Science 299: 520-521,

The myGrid Information Model,

The Open Grid Services Architecture,

Towards a Semantic Grid architecture.

Reasoning Services for the Semantic Grid

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

 Reasoning Services for the Semantic Grid 
Oscar Corcho 
The University of Manchester.  
Kilburn Building, Oxford Road, Manchester, M13 9PL, United Kingdom. 
Oscar.Corcho@manchester.ac.uk 
1 Background: The Semantic Grid and S-OGSA 
The Grid aims to support secure, flexible and coordinated resource sharing through providing a 
middleware platform for advanced distributing computing. Consequently, the Grid’s infrastruc-
tural machinery aims to allow collections of any kind of resources—computing, storage, data sets, 
digital libraries, scientific instruments, people, etc—to easily form Virtual Organisations (VOs) 
that cross organisational boundaries in order to work together to solve a problem. A Grid depends 
on understanding the available resources, their capabilities, how to assemble them and how to best 
exploit them. Thus Grid middleware and the Grid applications they support thrive on the metadata 
that describes resources in all their forms, the VOs, the policies that drive then and so on, together 
with the knowledge to apply that metadata intelligently.  
The Semantic Grid is a recent initiative to systematically expose semantically rich information 
associated with Grid resources to build more intelligent Grid services [1]. The idea is to make 
structured semantic descriptions real and visible first class citizens with an associated identity and 
behaviour. We can then define mechanisms for their creation and management and protocols for 
their processing, exchange and customisation. We can separate these issues from both the lan-
guages used to encode the descriptions (from natural language text right through to logical-based 
assertions) and the structure and content of the descriptions themselves, which may vary from 
application to application.  
In practice, work on Semantic Grids has primarily meant introducing technologies from the 
Semantic Web [2] to the Grid. The background knowledge and vocabulary of a domain can be 
captured in ontologies – machine processable models of concepts, their interrelationships and their 
constraints. Metadata labels Grid resources and entities with concepts, for example describing a 
job submission in terms of memory requirements and quality of service or a data file in terms of its 
logical contents. Rules and classification-based automatic inference mechanisms generate new 
metadata based on logical reasoning, for example describing the rules for membership of a VO 
and reasoning that a potential member’s credentials are satisfactory.  
1.1 S-OGSA 
The Grid has a reference architecture, called OGSA (Open Grid Service Architecture) [4], which 
defines a core set of capabilities and behaviours for Grid systems. However, currently the Seman-
tic Grid lacks a Reference Architecture or any kind of systematic framework for designing Seman-
tic Grid components or applications. In the context of the project OntoGrid 
(http://www.ontogrid.net/), which the project RSSGRID is associated to, an architecture called S-
OGSA has been recently proposed [6]. S-OGSA extends OGSA by explicitly defining a light-
weight mechanism that allows for the explicit use of semantics and defining the associated knowl-
edge services to support a spectrum of service capabilities.   
S-OGSA has three main aspects: the model (the elements that it is composed of and its interre-
lationships), the capabilities (the services needed to deal with such components) and the mecha-
nisms (the elements that will enable communication when deploying the architecture in an applica-
tion).  
 
S-OGSA Model. Although there is no standardized overall model of the Grid and its basic con-
cepts, there are project specific models [3,5], capability focused models emerging from the Global 
Grid Froum such as CIM (Common Information Model) and JSDL (Job Submission Description 
Language), and a vocabulary associated with OGSA. S-OGSA introduces the notion of Semantics 
 into the model of the Grid defining Grid Entities, Knowledge Entities (e.g. ontologies, rules, text), 
Semantic Bindings between these two for a Grid Entity to become Semantic Grid Entities. Seman-
tic Bindings are (possibly temporary) metadata assertions on Grid entities and are Grid resources 
with their own identity, manageability features and metadata.  
 
S-OGSA Capabilities. S-OGSA is a mixed economy of these semantically enabled and disabled 
services. We add to the set of capabilities that Grid middleware should provide (as defined by 
OGSA) the Semantic Provisioning Services and Semantically Aware Grid Services (Figure 1).  
Semantic Provisioning Services dynamically 
provision an application with semantic grid 
entities in the same way a data grid provisions 
an application with data. The services support 
the creation, storage, update, removal and access 
of different forms of Knowledge Entities and 
Semantic Bindings. Ontology services store and 
provide access to the conceptual models repre-
senting knowledge; reasoning services support 
computational reasoning with those conceptual 
models; metadata services store and provide 
access to semantic bindings and the annotation 
services generate metadata from different types 
of information sources, like databases, services 
and provenance data. 
Semantically Aware Grid Services exploit 
knowledge technologies to deliver their func-
tionality, for example metadata aware authenti-
cation of a given identity by a VO Manager 
service or execution of a search request over 
entries in a semantically enhanced resource 
catalogue. Sharing this knowledge brings flexi-
bility to components and increases interoperability.  
 
S-OGSA Mechanisms. All this conceptual work grounds out into concrete Grid modeling ele-
ments. Specifically, S-OGSA OntoGrid’s implementation builds on Globus Toolkit 4, grounding 
to WS-RF (Web Services Resource Framework), incorporating S-OGSA entities into the CIM 
Resource Model. These groundings demonstrate how semantic bindings can be incarnated in the 
form of stateful Grid resources, including bindings on inter-service messages that are not strictly 
Grid entities but nonetheless useful.  
2 Reasoning Services in S-OGSA 
The project RSSGRID is specifically focused on the development of reasoning services, 
which are part of the semantic provisioning services described in the S-OGSA architec-
ture. RSSGRID considers the following two situations in the adaptation and refinement 
process of reasoning infrastructure: 
a) Knowledge in the Semantic Grid is distributed among Grid resources. Reasoning services 
will have to gather knowledge distributed in many sources and process it to fulfil a task. 
b) Reasoning in the Semantic Grid can be performed collaboratively by distributed Grid 
resources. In order to allow a good scaling up of reasoning services, they will surely have to dis-
tribute their reasoning workload among distributed resources so that they can operate more effi-
ciently. 
Figure 1: The S-OGSA semantic provisioning 
services positioned in the OGSA services  
 Taking into account these situations (knowledge and reasoning distribution), common problems of 
Grid computing will also appear in the Semantic Grid. The most relevant problems that we will 
deal with are heterogeneity, scalability and adaptability: 
a) Regarding heterogeneity, we will deal with knowledge distributed among Semantic Grid re-
sources, which will be heterogeneous in different aspects: it will be represented in different lan-
guages and formats (such as the Semantic Web languages RDF – Resource Description Frame-
work –, RDF Schema, or OWL – Web Ontology Language –), it will consider different vocabular-
ies or ontologies, etc. Some work has been already done to deal with distributed knowledge in the 
context of the Semantic Web, regarding knowledge localization and format heterogeneity. How-
ever, the current solutions are not mature enough yet.  
b) Regarding scalability, we will improve the efficiency of complex reasoning processed by dis-
tributing their execution in several resources. We must note that the efficiency gaining will not be 
linear with regard to the number of resources used, since we will have to consider the overhead 
inherent to the dispatching of reasoning subprocesses, latencies, etc. Work has been also done in 
the past in this issue (from Problem Solving Methods to Internet reasoning services, and from 
domain oriented solutions to generic ones), which will be improved and adapted to the Grid archi-
tecture. 
c) Regarding adaptability, we will consider the possibility of failures of resources and of their 
reasoning processes. This will deal to problems when trying to ensure that the results delivered by 
a reasoning process are complete and/or correct, whether we are considering all the relevant con-
tent, etc. RSSGRID’s innovation will go in the direction of facing failures in reasoning resources 
and processes with guarantees. Finally, we will provide information about the quality of service by 
a continuous process of evaluation (which will be also innovative itself). 
Acknowledgements 
I would like to give thanks to the OntoGrid team at the University of Manchester, with 
whom I have worked on the proposal of the S-OGSA reference architecture. Besides, this 
work is supported by the Marie Curie Intra-European Fellowship “RSSGRID” (contract 
number 006668) and is being deployed in the context of the EU FP6 OntoGrid project 
(STREP 511513).  
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