Chapter 4 XML Processing

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You can generate the content objects manually or automatically by using

XML data binding technologies such as JAXB. Furthermore, you can combine

these XML serializable components into composite entities with corresponding

composite schemas.

When combined with the  meet in the middle  approach discussed previ 

ously, you can apply XSLT transformations to convert XML documents conform 

ing to external vertical schemas into your application's supported internal generic

schemas. Transformations can also be applied in the opposite direction to convert

documents from internal generic schemas to external vertical schemas. 

For example, Figure 4.8, which illustrates XML componentization, shows a

PurchaseOrderBean 

composite entity and its two components, 

AddressBean

 and

LineItemBean

. The schemas for the components are composed in the same way

and form a generic composite schema. Transformations can be applied to convert

the internal generic composite 

PurchaseOrder

 schema to and from several exter 

nal vertical schemas. Supporting an additional external schema is then just a

matter of creating a new stylesheet.

4.3.5 Choosing Processing Models

An XML based application may either apply its business logic directly on con 

sumed or produced documents, or it may apply its logic on domain specific objects

that completely or partially encapsulate the content of such documents. Domain 

specific objects are Java objects that may not only encapsulate application domain 

specific data, but may also embody application domain specific behavior.

An application's business logic may directly handle documents it consumes or

produces, which is called a document centric processing model, if the logic: 

  Relies on both document content and structure 

  Is required to punctually modify incoming documents while preserving most 

of their original form, including comments, external entity references, and so 

forth

In a document centric processing model, the document processing may be

entangled with the business logic and may therefore introduce strong dependen 

cies between the business logic and the schemas of the consumed and produced

documents the  meet in the middle  approach (discussed in  Mapping Schemas

to the Application Data Model  on page 143) may, however, alleviate this prob 

lem. Moreover, the document centric processing model does not promote a clean