1. Prof. Neeraj Bhargava
Pooja Dixit
Department of Computer Science
School of Engineering & System Sciences
MDS, University Ajmer, Rajasthan, India
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2. The architecture for grid computing is defined in the Open
Grid Services Architecture that describes the overall structure
and the services to be provided in grid environments .
Figure depicts the network’s role in supporting a
(standardized) grid. Figure is the reference diagram that
illustrates the OGSA.
The companion implementation standard, the OGSI, is a
formal specification of the concepts described by the OGSA; it
specifies a set of service primitives that define a nucleus of
behavior common to all Grid Services .
OGSI, in effect, is the base infrastructure on which the OGSA
is built, as illustrated pictorially in Figure.
As just noted, OGSA is a distributed interaction and
computing architecture that is based around the grid service
concept, assuring interoperability on heterogeneous systems.
As a result, different types of systems can communicate and
share information. OGSA allows system composition to
perform a specific task, or solve a challenging problem, by
using distributed resources over the interconnecting network.
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3. The grid architecture is now being developed based on
Internet protocols (for example, communication, routing, file
transfer, name resolution, etc.) and services.
The grid architecture defined in OGSA leverages the emerging
Web services to define the WSDL interfaces that are relevant to
the grid environment.
WSDL is an XML-based language used to describe the services
that a business offers, and to provide a mechanism for
individuals and businesses to access these services in an on-
line fashion (WSDL is derived from Microsoft’s SOAP and IBM’s
Network Accessible Service Specification Language).
WSDL is used in the context of UDDI. UDDI is an XML-based
global registry for businesses that enables these businesses
to list themselves and their services on the Internet.
These conventions and other OGSI mechanisms associated
with grid service creation and discovery provide for the
controlled, fault-resilient, and secure management of the
distributed and often long-lived “state” that is commonly
required in advanced distributed applications2.
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4. OGSA takes the view that a grid service is simply a Web service that
conforms to a particular set of conventions; that is, grid services are
defined in terms of standard WSDL with some (minor) extensions.
With this approach,
OGSA is driving the hosting environment to accept modifications or
additions for supporting the repertoire of grid services .
To further clarify what a grid service is, note that an OGSI-compliant
grid service defines a subclass of Web services whose ports all
inherit capabilities from a standard grid service port (so a grid
service is a Web service that conforms to a set of conventions that
provide for controlled, fault-resilient, and secure management of
stateful services).
The running of an individual service (for example, an information
query) is called a service instance. Services and service instances can
be “lightweight” and transient, or they can be long-term tasks that
require “heavy-duty” support from the grid.
Services and service instances can be dynamic or interactive, or they
can be batch processed. Service can run at scheduled times, or they
can run at arbitrary times .
grid services include: Discovery Lifecycle State management
Service groups Factory Notification Handle map
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6. OGSA reliance on OGSI
MOTIVATIONS FOR STANDARDIZATION
Data management. For a grid to work effectively, there is a need
to store information and distribute it. Without a standardized
method for describing the work and how it should be exchanged,
one quickly encounters limits related to the flexibility and
interoperability of the grid.
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7. Dispatch management. There are a number of approaches that can be used
to handle brokering of work units and to distribute these work units to client
resources. Again, not having a standard method for this restricts the service
providers that can connect to the grid and accept units of work from the
grid; this also restricts the ability of grid services users to submit work.
Information services. Metadata6 about the grid service helps the system to
distribute information. The metadata is used to identify requesters (grid
users), providers, and their respective requirements and resource availability.
Again, without a standard, one can only use specific software and solutions
to support the grid applications.
Scheduling. work must be scheduled across the service providers to ensure
they are kept busy. To accomplish this, information about remote loads must
be collected and administered. A standardized method of describing the grid
service enables grid implementations to specify how work is to be scheduled.
Security. Without a standard for the security of a grid service and for the
secure distribution of work units, one runs the risk of distributing
information to the “wrong” clients. Although proprietary methods can
provide a level of security, they limit accessibility.
Work unit management. Grid services require management of the
distribution of work units to ensure that the work is uniformly distributed
over the
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8. Increased effective computing capacity. When the resources utilize
the same conventions, interfaces, and mechanisms, one can
transparently switch jobs among grid systems, both from the
perspective of the server as well as from the perspective of the
client. This allows grid users to use more capacity and allows clients
a more extensive choice of projects that can be supported on the
grid. Hence, with a gamut of platforms and environments supported,
along with the ability to more easily publish the services available,
there will be an increase in the effective computing capacity.
Interoperability of resources. Grid systems can be more easily and
efficiently developed and deployed when utilizing a variety of
languages and a variety of platforms. For example, it is desirable to
mix service-provider components, work-dispatch tracking systems,
and systems management; this makes it easier to dispatch work to
service providers and for service providers to support grid services.
Speed of application development. Using middleware (and/or
toolkits) based on a standard expedites the development of grid-
oriented applications supporting a business environment. Rather
than spending time developing communication and management
systems to help support the grid system, the planner can, instead,
spend time optimizing the business/algorithmic logic related to the
processing the data.
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