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Subject: RE: [ws-caf] Context example assignments



Here’s my context example homework.   I apologize for getting this out a bit late but my laptop died Friday and it threw me off track since I had a couple of deadlines to meet.


Mine was the database/file/device example.  Here’s what a possible child context could look like for this example:



      <database-name> SQL-DB </database-name>

      <file-name> Index-S-file </file-name>

      <display-address> PocketPc25 </display-address>



This example illustrates how shared context can be used to pass into a composite application the definition of a database name, file name, or device name for use by the web services in the composite.


I do not think this example shows something that can be easily propagated in a SOAP message since file and database handles tend to be operating system specific and also tend to be associated with an individual or specific operating system process.


However, if a composite application wished to share a database, file, or display device among multiple Web services, shared context managed by the WS-Context defined context service would be a way to do it. The advantage of using the context mechanism for this purpose would be that it’s easier to change the database, file, or device address if it’s defined in an external structure than within the application code.


In this example, the context structure would be used to input the initial database, file, or device name into the application. The initial Web service in the composite would then be responsible for obtaining the database or file handle or device ID and updating the context to include it.  So the updated context would contain the database or file handle or device ID as a kind of opaque value that other Web services in the composite could use, by accessing the common shared context through the context service.


I think there would be some limitations to the extent to which this type of context could be shared, since it tends to be operating system or database system specific, but on the other hand a lot of file systems and database management systems are now distributed, or at least network addressable. For device IDs I suppose for this to work across the network the ID would have to be an IP address rather than an operating system’s device ID or some internal ID like a computer name.





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