Java Reference
In-Depth Information
XHTML documents must be all lowercase. And XHTML requires that all tags must
be closed. In HTML, this isn't always necessary. There are other differences, most
of which are meant to bring the HTML standard into compliance with stricter lan-
guage and parsing rules of XML.
W
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XML
XML is important to the business application developer because it finally offers a
standard language and syntax suitable for intersystem data transfer. Every business
system needs to interact with at least one other system in some fashion. The other
system can be an external system at a business partner. Or the other system might
be an internal system (perhaps a data warehouse) that needs information from an-
other internal system (for example, the production order entry system).
Before the widespread use of XML, the standard technique used to transfer in-
formation between two business systems has been to write a set of interface pro-
grams. System one would create an interface file with the required information. Or
system one might write the information to interface tables in a database. The target
system will read that information, validate it, and update the target system data-
base. In rare cases, the source or target system will access the other system's data-
base directly, but this approach requires simultaneous access to both systems and
developers who understand both systems.
Interface systems often require serious planning and attention. Carefully pre-
defined and documented interface format specifications are necessary so that each
system's developers can understand what is required. The normal process flows in
both systems need to be accounted for. Most important, the data transformation
requirements are embedded in the interface system logic.
As business requirements and the systems that support these requirements
change, interface system requirements may change as well. Implementing these
changes will require careful coordination and integrated testing plans, even if only
two systems are involved. When multiple target systems or their interfaces need to
be adjusted for a single-source system, modifications to the existing integration
process can become unmanageable. If multiple business partners' systems are in-
volved, one can only hope that their interface specifications are adaptable and up to
date and that the original developers are still around.
XML promises to improve this process significantly. As general purpose, self-
describing data repositories, XML files are readily accessible by multiple systems.
Intricate coordination and data mapping designs are not as crucial, since the XML
files describe themselves. Systems need only to create XML documents based on an
agreeable DTD or to input data from an XML file based on their own require-
ments. Modifications to the source or the target system do not need to be so closely
