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Frequently Asked Questions

Grid

1. What is the Grid Middleware?

What is Grid middleware? Grid Middleware refers to the security, resource management, data access, instrumentation, policy, accounting, and other services required for applications, users, and resource providers to operate effectively in a Grid environment. Middleware acts as a sort of 'glue' which binds these services together.

2. What is OGSA-DAI / OGSA / DQP?

Open Grid Services Architecture Data Access and Integration ( OGSA-DAI ) is an Open Grid Services Architecture ( OGSA ) interface for accessing and manipulating grid-enabled XML and relational databases. OGSA-DAI provide a number of services that extend the base services facilitated by Open Grid Services Infrastructure ( OGSI ):

Grid Data Service ( GDS )

GDS provides standard mechanism for accessing database services.

Grid Data Service Factory ( GDSF )

GDSF establishes a database service instance that the client can connect directly to in order to perform operations on the data of interest.

Database Access and Integration Service Group Registry ( DAISGR )

DAISGR is used to identify available database services. The software is developed by The Globus Alliance and UK e-Science Grid Core Project and can be downloaded from the OGSA-DAI project web site.

More information: http://www.ogsadai.org.uk/

OGSA-DQP is an extension of OGSA-DAI that provides a service-based distributed query processor. It supports the evaluation of queries over collections of potentially remote relational data services.

3. What is GT?

GT (Globus Toolkit) is a middleware sytem which allows building grids (connecting different computer systems). It is being developed by an open source community under the lead of the Globus Alliance.

It allows users to share computing power, databases, and other tools securely online across corporate, institutional, and geographic boundaries without sacrificing local autonomy. The toolkit includes software services and libraries for resource monitoring, discovery, and management, plus security and file management.

The Security is provided by the built in GSI (Globus Security Infrastructure). This provides the ease of use enabling a single sign-on on all machines of the GRID using X509 Certificates.

More information: http://www.globus.org/ .

4. What is Condor?

Condor is a job control system, which allows to run individual jobs (programmes or routines) on a pool (cluster) of machines.

Each individual job will run on a single machine of the cluster. Condor can be used for large computing tasks that can easily be split into multiple small or medium sized computations. The Condor System will deal with the distribution of the individual small computations across the machines which were assigned to the Condor pool.

More information: http://www.cs.wisc.edu/condor/

5. What is SRB?

The Storage Resource Broker ( SRB ) provides a uniform interface to a virtual distributed data storage resource where users can access files and database objects. The physical location of the data is abstracted from the user as it implements a logical namespace. The metadata on data-objects (files), users, groups, resources, and collections are maintained in a Metadata Catalog ( MCAT ) which is stored in a relational database management system ( RDBMS ). This provides a way to access data sets and resources based on their attributes or logical names rather than their names or physical locations. There are four main components to SRB :

The Metadata Catalogue ( MCAT )

The MCAT database is a metadata repository that provides a mechanism for storing information used by the SRB system. It includes both the Internal system data required for running the system and the Application (user) metadata regarding data sets being brokered by SRB .

The MCAT -Enabled SRB Server.

The MCAT -Enabled SRB Server is (at least) one of the SRB Servers installed on a node that can access the MCAT database. It works directly against the MCAT database to provide SRB Services. All other SRB Servers interact through the MCAT Server.

The SRB Storage Server.

The SRB Storage Server is a middleware application that accepts requests from clients and obtains/queries/manages the necessary data sets. It queries the MCAT SRB Server to gather information on datasets and supplies this back to the SRB client.

The SRB Client.

The SRB Client provides a user interface to send requests to the SRB server. There are four main interfaces:

  • Command line (S-Commands)
  • MS Windows (InQ)
  • Web based (MySRB)
  • Java ( JARGON )

 

SRB data flow [Berrisford, 2005]

For authentication and authorization of data SRB can utilize the Grid Security Infrastructure ( GSI ). The source distribution is freely available to academic and non-profit organizations. SRB is being actively developed at the San Diego Supercomputer Center ( SDSC ).

More information: http://www.sdsc.edu/srb/

6. What is OMII?

OMII (Open Middleware Infrastructure Institute) provides a web service infrastructure for building grid applications.

This web service infrastructure is an open source system that addresses the user requirements of combining ease of use with a secure environment which focuses on the needs of distinct yet important stakeholders within Grid computing: the Service Provider and the Client.

More information: http://www.omii.ac.uk/

7. What are Web Services

A web service is a collection of protocols and open standards which provide interoperability between different applications on various platforms in order to exchange data over computer networks. Web services use a number of standards:

  • XML
  • WSDL
  • UDDI
  • WS -Security

Web services can be deployed by using application server software such as Axis, Jakarta Tomcat server, ColdFusion MX, Java Web Services Development Pack, Microsoft .NET, WebSphere Application Server, and Zope.

Simple Object Access Protocol ( SOAP ) is an XML based protocol for accessing a Web Services via HTTP .

Web Services Description Language ( WSDL ) is a XML document that describes the public interface of a web service using four major elements:

<portType> </portType>

describes the interfaces exposed by the web service.

<message> </message>

describes the data elements of an operation used by the web service.

<types> </types>

describes the data types used by the web service.

<binding> </binding>

describes the message format and communication protocols for each port used by the web service.

The WSDL port element, <portType></portType>, is the most important as it defines the web service in terms of its operations and messages. WSDL is used in combination with SOAP and XML Schema to provide web services over the internet. The client connecting to a web service can read the WSDL to determine what functions are available on the server and can call these using SOAP .

eXtensible Markup Language ( XML ) is a markup language designed to facilitate the sharing of structured text and information across the Internet.

XML was introduced by W3C to transform the World Wide Web from a publishing medium into an applications processing medium. XML takes the concept of markup beyond text formatting to data structures. XML is not an SGML application, but is instead considered a subset of SGML because it borrows a subset of SGML semantics. Two traditional technologies have also had a major influence the growth of XML : relational databases and object-oriented programming. The Document Object Model makes XML elements available through a comprehensive set of standard interfaces.

Universal Description, Discovery and Integration ( UDDI ) is a platform-independent directory service for the discovery of web service interfaces described using WSDL and SOAP .

More information:

8. What is Growl?

GROWL is the Grid Resources On Workstation Library which provides a client interface to a Grid programming environment.

More information: http://www.growl.org.uk