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The North-East Regional e-Science Centre is involved in a large number of
research projects that rely on the design and development of a Grid-based
infrastructure. Building a large number of different infrastructures would
be time-consuming, difficult and risky; currently available Grid middleware
is relatively immature and subject to frequent change, while relevant
knowledge and experience among e-Science researchers is understandably very
limited. A further issue is that many e-Science projects—both at Newcastle
and elsewhere—are currently based on Web Services, with the intention of
moving to Grid Services at some point in the future. The method of making
the transition is not yet clear, nor is the extent of the extra work, delays
and risks this will introduce into projects.
 Consequently, it was decided
to analyse the requirements of all the Newcastle projects and to design and
build a common Core Grid Middleware package that, in its initial release,
will incorporate four key Grid Services (Figure 1).
Following that initial release, the Core Grid Middleware will continue to
evolve by incorporating the “best-of-breed” OGSA Services produced by the
Grid community or, if deemed necessary, developing them in house.
The experience gained from the development and deployment of the Core
Grid Middleware will be valuable for the UK e-Science community wishing to
adopt the Open Grid Services Architecture; for any new Grid Services related
research projects; and as feedback to the process of building the UK Grid
Services-based infrastructure and the Open Middleware Infrastructure
Institute.
OGSA-DAI
Many of the research projects in which the NEReSC is involved require
access to database management systems over the Grid. The Open Grid Services
Architecture – Database Access and Integration (OGSA-DAI) service provides a
consistent way to access relational and XML data on the Grid. The OGSA-DAI
implementation is included as is in the Core Grid Middleware.
OGSA-DQP
NEReSC is directly involved in the design and implementation of the OGSA-DAI
Distributed Query Processing (DQP) Grid Service (reference to your section
on OGSA-DAI DQP), which enables Grid applications to run queries on
distributed data resources. A number of e-Science research projects will
greatly benefit from the inclusion of OGSA-DAI DQP in the initial release of
the Core Grid Middleware.
Workflow
The ability to capture and enact computations is important for all the
e-Science projects. Existing work on workflow execution in the myGrid
project is the basis for the Workflow Enactment Grid Service (WEGS) for the
Core Grid Middleware. Currently, the myGrid enactment engine is based on Web
Services and so NEReSC is producing WEGS to be OGSI compliant.
The WEGS in the initial release of the Core Grid Middleware will accept
workflows written in Web Services Flow Language (WSFL) and Scufl. However,
NEReSC is already evaluating the possibility of providing support for the
Business Process Execution Language for Web Services (BPEL4WS) in addition
to WSFL.
NEReSC is planning to follow the work of the GGF working groups in the
important area of workflow/business process composition and provide support
for the Grid workflow standard when that is made available.
Notification
The expected dynamic and distributed nature of Grid Applications means
that a facility is necessary for informing interested parties of changes in
data, Grid Service status, application-specific events, etc. The
Notification Grid Service (NGS) is based on the one produced within the
myGrid project. The myGrid Notification Service provides a way for myGrid
Services to publish events and/or register interest in published events.
Like the workflow enactment engine, the myGrid Notification Service is
based on Web Services and so it is being adapted to be OGSI compliant. The
OGSI specification describes a notification portType and Service Data
Elements (SDEs) through which NGS will provide the myGrid Notification
Service functionality.
Future Work
The work being carried out to port the myGrid Workflow Enactment and
Notification Web Services to be Grid Services will develop valuable
knowledge about the issues and effort required to achieve this
conversion–something that will be useful to the many UK e-Science projects
planning to carry out this transition at some point.
After the initial release, new services will be added to the core set
over time, in response to requirements and availability. The main candidates
will be the services specified by the OGSA standardisation activity (Figure
2), but it may necessary to pre-empt standardisation in order to meet
project requirements. In most cases “best-of-breed” services will be
identified and integrated, provided that an open-source implementation is
available. However it may sometimes be necessary to develop services if
there is a requirement and no implementation exists.
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