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Designing XML Based Applications

separation between business and XML programming skills, especially when an

application developer who is more focused on the implementation of the business

logic must additionally master one or several of the XML processing APIs.

There are cases that require a document centric processing model, such as: 

  The schema of the processed documents is only partially known and therefore 

cannot be completely bound to domain specific objects; the application edits 

only the known part of the documents before forwarding them for further pro 

cessing.

  Because the schemas of the processed documents may vary or change greatly, 

it is not possible to hard code or generate the binding of the documents to do 

main specific objects; a more flexible solution is required, such as one using 

DOM with XPath.

A typical document centric example is an application that implements a data 

driven workflow: Each stage of the workflow processes only specific information

from the incoming document contents, and there is no central representation of the

content of the incoming documents. A stage of the workflow may receive a docu 

ment from an earlier stage, extract information from the document, apply some

business logic on the extracted information, and potentially modify the document

before sending it to the next stage.

Generally, it is best to have the application's business logic directly handle

documents only in exceptional situations, and to do so with great care. You should

instead consider applying the application's business logic on domain specific

objects that completely or partially encapsulate the content of consumed or pro 

duced documents. This helps to isolate the business logic from the details of XML

processing.

Keep in mind that schema derived classes, which are generated by JAXB and

other XML data binding technologies (see  XML Data Binding Programming

Model  on page 169), usually completely encapsulate the content of a document.

While these schema derived classes isolate the business logic from the XML pro 

cessing details specifically parsing, validating, and building XML documents 

they still introduce strong dependencies between the business logic and the

schemas of the consumed and produced documents. Because of these strong

dependencies, and because they may still retain some document centric character 

istics (especially constraints), applications may still be considered document

centric when they apply business logic directly on classes generated by XML