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can filter the document to retrieve only this information. However, since it may

need to pass the entire invoice all the data fields in the invoice to the next step

in the workflow, the workflow manager must preserve the entire document. The

workflow manager can accomplish this using flexible mapping. (See  Flexible

Mapping  on page 148.)

On the other hand, you may want to apply data filtering before sending infor 

mation. For example, a credit card processing component of a workflow may need

to send credit information. The component should send only information required

for privacy protection and should use data filtering to remove information that

need not be passed to another application.

Filtering can be applied at the database level, too. Using filtering, you can

obtain a simplified view of the data tailored to a particular application. In addition,

using EJB container managed persistence for data transformation makes it easier

to filter data. The container managed persistence mapping tools let you select a

subset of the database schema, and this is analogous to filtering. If you are using

the JDBC RowSet approach, you need only select the columns for the data that

you care about.

You can also write facades that appropriately filter the data. In this case, the

client code accesses data only through these facades.

6.5

Guidelines for Integration

Now that we've examined  and techniques, let's look

at some guidelines for integrating enterprise applications with EIS systems. 

We examine guidelines for integrating legacy systems, particularly home 

grown systems, and guidelines for using command beans. Although not as

common, we mention guidelines for achieving integration by using metadata, reg 

istries, and versioning and evolution.

6.5.1 Integrating Custom Legacy Systems

Most enterprises have home grown or custom EISs, also referred to as one off sys 

tems, and these systems need to be integrated. As we have already seen, connectors

are the best solution for integrating EISs in a J2EE environment. However, because

these are custom systems, there are no off the shelf or vendor provided connectors

available for them as there are for well known EISs. As a result, you may have to

write your own connector for a home grown EIS. The recommended way to write a

connector is to use a connector builder tool. A tool such as this not only generates a