Chapter 4 XML Processing

189

Internet

Intranet

Web Service 

Order 

Web Service  Nonvalidated 

Front End

Processing 

Valid 

Supplier 

Client

Center

XML

Web Service 

XML

(Trusted)

Legend

Validate always

Supplier

Web Service 

Validate optionally

Figure 4.14

Validating Only When Necessary

In other words, when you are both the producer and consumer of XML docu 

ments, you may use validation as an assertion mechanism during development,

then turn off validation when in production. Additionally, during production vali 

dation can be used as a diagnostic mechanism by setting up validation so that it is

triggered by fault occurrences. 

4.5.5 Reduce the Cost of Referencing External Entities

Recall that an XML document may be the aggregation of assorted external entities,

and that these entities may need to be retrieved across the network when parsing. In

addition, the schema may also have to be retrieved from an external location. Exter 

nal entities, including schemas, must be loaded and parsed even when they are not

being validated to ensure that the same information is delivered to the application

regardless of any subsequent validation. This is especially true with respect to

default values that may be specified in an incoming document schema.