Data Services

A data service is a point of contact for clients who wish to access, query or update a data resource, or perform other data-related actions using OGSA-DAI. A data service offers a document-oriented interface which accepts OGSA-DAI perform documents from clients and returns response documents to clients. A data service may typically offer other OGSA-DAI operations, for example data transport-related operations.

A data service exposes 0 or more data service resources which are described here.

A data service provides a number of operations which allow information about the service to be retrieved and also provides access to the data service resources exposed by that data service.

Some operations are targetted at the service. Most however will be targetted at a particular resource exposed by the service. How this resource is identified is specific to the version of OGSA-DAI:

• In OGSA-DAI WSI it is specified in postfix to the service URL. For example targetting an operation invocation to the resource ResourceOne exposed by service:

  http://localhost:8080/axis/services/ogsadai/DataService
  

  means that the following URL is used when communicating with the OGSA-DAI server

  http://localhost:8080/axis/services/ogsadai/DataService/DAIResourceOne
  

• In OGSA-DAI WSRF the resource is specified in WS-Addressing information added to the SOAP header of the operation request message.
• Our client toolkit means you don't have to worry about such details!

Data services are intended to be long-running.

Data Operations

The Perform Operation

• Inputs:
  • A perform document.
• Outputs:
  • A response document.

This operation is directed at a specific data service resource and is the key OGSA-DAI operation provided by a data service.

This operation provides a document-oriented interface for database requests in which perform documents are used by clients to specify activities on the data resources and data managed by a specific data service resource. The status of the operations, delivery locations and, often, data itself, is returned to a client in a response document.

The Terminate Operation

This operation is a place holder for future development. It currently does nothing.

The PutFully Operation

• Inputs:
  • The name of a session known to a data service resource.
  • The name of an open input stream known to the session.
    • The session name and stream name are expected to be conjoined with a colon (:).
  • Data - a string, a chunk of valid XML or a byte array.
• Outputs: None.

This operation is directed at a specific data service resource and supports data delivery between data services and clients. The operation puts a complete set of data onto a specific input stream of a specific session known to the data service resource.

The PutBlock Operation

• Inputs:
  • The name of a session known to a data service resource.
  • The name of an open input stream known to the session.
    • The session name and stream name are expected to be conjoined with a colon (:).
  • A block of data - a string, a chunk of valid XML or a byte array.
    • A special control block sent on its own indicates to the recipient that all the data has been communicated. This block is a qualified name: {http://ogsadai.org.uk/namespaces/2005/10/properties}NoMoreData
• Outputs: None.

This operation is directed at a specific data service resource and supports data delivery between data services and clients. The operation puts a block of data - part of a larger set - onto a specific input stream of a specific session known to the data service resource.

The GetFully Operation

• Inputs:
  • The name of a session known to a data service resource.
  • The name of an open output stream known to the session.
    • The session name and stream name are expected to be conjoined with a colon (:).
• Outputs:
  • Data - a string, a chunk of valid XML or a byte array.

This operation is directed at a specific data service resource and supports data delivery between data services and clients. The operation gets (or pulls) a complete set of data from a specific output stream of a specific session known to the data service resource.

The GetNBlocks Operation

• Inputs:
  • The name of a session known to a data service resource.
  • The name of an open output stream known to the session.
    • The session name and stream name are expected to be conjoined with a colon (:).
  • The number of blocks of data to be retrieved.
• Outputs:
  • A block of data - a string, a chunk of valid XML or a byte array.
    • A special control block received on its own indicates to the recipient that all the data has been communicated. This block is a qualified name: {http://ogsadai.org.uk/namespaces/2005/10/properties}NoMoreData

This operation is directed at a specific data service resource and supports data delivery between data services and clients. The operation gets (or pulls) a specific number of blocks of data - part of a larger set - from a specific output stream of a specific session known to the data service resource.

The GetBlock Operation

This operation is equivalent to calling GetNBlocks where the number of blocks requested is 1.

Property and State Operations

The GetResourceProperty Operation

• Inputs:
  • Qualified name of a data service resource property.
    • The properties of data service resources are listed on the data service resources pages.
• Outputs:
  • Data service resource property value.

This operation is directed at a specific data service resource - and can be used to get a named property of a data service resource.

The GetMultipleResourceProperties Operation

• Inputs:
  • Qualified names of one or more data service resource properties.
    • The properties of data service resources are listed on the data service resources pages.
• Outputs:
  • Data service resource properties values.

This operation is directed at a specific data service resource and can be used to get a set of named properties of a data service resource.

The QueryResourceProperties Operation

• Inputs:
  • An XPath query expression.
    • The properties of data service resources are listed on the data service resources pages.
• Outputs:
  • The XML fragments of each data service resource property which matches the XPath expression.

This operation is directed at a specific data service resource - and can be used to run an XPath query over the properties of a data service resource.

This operation is not supported in OGSA-DAI WSI.

Service Operations

The ListResources Operation

• Inputs: none.
• Outputs:
  • List of names of data service resources.

This operation is not specific to a data service resource but is an operation belonging to the service. It allows a client to get the IDs of all the data service resources currently known to the service.

The GetVersion Operation

• Inputs: none.
• Outputs:
  • Version string, for example OGSA-DAI WSI 2.1 or OGSA-DAI WSRF 2.1.

This operation is not specific to a data service resource but is an operation belonging to the service. It allows a client to get a string indicating the flavour and version of OGSA-DAI from which the service was produced.