182

Performance Considerations

 //Sun Microsystems, Inc.  

J2EE Blueprints Group//DTD Invoice 1.0//EN: /com/sun/j2ee/blue 

prints/xmldocuments/rsrc/schemas/Invoice.dtd

# XSD URI to physical location (URL or resource path)

http\://blueprints.j2ee.sun.com/LineItem: /com/sun/j2ee/blue 

prints/xmldocuments/rsrc/schemas/LineItem.xsd

http\://blueprints.j2ee.sun.com/Invoice: /com/sun/j2ee/blue 

prints/xmldocuments/rsrc/schemas/Invoice.xsd

Code Example 4.12

A Simple Entity Catalog

Although simple implementations such as Code Example 4.11 solve many of

the common problems related to external entity management, developers should

bear in mind that better solutions are on the horizon. For example, organizations

such as the Oasis Consortium are working on formal XML catalog specifications.

(See the Web site 

http://www.oasis open.org

 for more information on entity

resolution and XML catalogs.)

In summary, you may want to consider implementing a custom entity resolu 

tion or, even better, resort to a more elaborate XML catalog solution in the fol 

lowing circumstances:

E

To protect the integrity of your application against malicious modification of 

external schemas by redirecting references to secured copies (either local cop 

ies or those on trusted repositories)

E

During design and, even more so, during production, to protect your applica 

tion against unexpected, legitimate evolution of the schemas upon which it is 

based. Instead, you want to defer accounting for this evolution until after you 

have properly assessed their impact on your application.

E

To improve performance by maintaining local copies of otherwise remotely 

accessible schemas.

4.5

Performance Considerations

It is important to consider performance when processing XML documents. XML

document processing handling the document in a pre  or post processing stage to

an application's business logic may adversely affect application performance