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<H1><nop>IVOA Grid & Web Services: Asynchronous services</H1>

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---++ Overview
Services are defined as being asynchronous when an operation on a web service starts some activity and returns immediately, leaving the activity running remotely. This asychronicity is useful in making a robust VO and is already used in some VO prototypes, e.g. Astrogrid's Common Execution Architecture (CEA). A [[AsynchronousActivityProposal][conceptual proposal]] for managing the activities was drawn up and presented to IVOA in 2004. This was formalized into the _Universal Worker Service (UWS)_ pattern.

<br/>
---++ Universal Worker Service
UWS proposes that a minimal interface supports job creation, polling of job status and retrieval. A fuller interface would also allowing requesting an estimate of the duration of a job amd restarting a failed job from its last checkpoint.

UWS-PA is an instantiation of the UWS pattern for parameterized applications (PA), i.e. applications whose input and output arguments can be expressed as a set of key-value pairs. CEA is an implementation of UWS-PA.

---+++ Specification
The latest version of the UWS propasal is v0.3. It introduces a REST binding as an alternative to SOAP: 

   * [[%ATTACHURL%/UWS-0.3.pdf][UWS v0.3]]

---+++ Discussion

   * [][[Discussion page for specification]]
 
---+++ History
These are older version of the UWS specification:

   * [[%ATTACHURL%/uws.html][UWS v0.1]]
   * [[%ATTACHURL%/UWS-0.2.doc][UWS v0.2]].


<br/>
---++ Background reading
   * [[http://forge.gridforum.org/projects/dais-wg/document/Scenarios_for_Mapping_DAIS_Concepts/en/3][Comparison of systems for contextual web services]]
   * [[Common Execution Architecture]] (CEA)


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Topic revision: r1 - 2008-04-24 - MatthewGraham

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