Michael Kay on designing applications using a workflow-basedapproach

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,
 
Michael Kay has written an excellent article[1] on how to design applications using an XML workflow-based approach.
 
Workflow applications are those applications where documents are moved around a community of people who each perform on it.

Here are some of the key points in the article:

1. XML encourages you to change the way you think about application design. 

2. Design XML documents based on the process in which they will be used (process-driven design). 

3. Designing XML documents without any consideration of how the data will be used, because you don't want to limit how it will be used, is generally a bad idea. 

4. XML generally plays a different role in a system than does a database:

   - A database sits around on a mainframe waiting for 
     people to do queries.

   - XML is used for moving data around. 

5. Designing XML like you design databases often doesn't work too well. 

6. Got a paper-based workflow? Mimic each paper document as an XML document. Advantages:

   - Users understanding of the paper documents transfers 
     readily to understanding the XML documents.

   - Users questions (queries) of the paper documents 
     transfers readily to queries on the XML documents. 

7. Design applications around the notion of data on the move, rather than data in a warehouse. 

8. The kind of database needed in workflow-based applications is likely to be very different than with traditional application design, because its primary role is not to support ad-hoc queries, but to support workflow.

    - Use an XML database
 
9. Centralized approach to data storage: the documents live in some central (XML) database, and all you send around are URLs that point to them. Advantages:

    - No risk of the documents getting lost or delayed.

    - You have the ability to find out what's happening 
      at any point in time right across the system. 

10. Workflow-based applications can be implemented using just the XML technologies, without use of imperative languages such as Java, C#, and there are multiple reasons for doing so.

/Roger
 
[1]  http://www.stylusstudio.com/whitepapers/xml_workflow.pdf