| 3.3 Schema Controlled XML The early stage XML usages we have seen at major data centers reminds
us of source control in the early days of the computer industry. Then, programs were
written on an ad hoc basis, with no implementation standards, no source code library
system, no global routines, and no COPY books. Every program had its own unique
description of data elements and local implementation of common logic, leading to higher
error rates and greater maintenance costs. If XML usage at your site is allowed to develop
along a similar path and you expect to have more than a few trivial usages, then we
recommend that any use of XML be reconsidered.
However, there is a mechanism provided for in the XML
specification that allows for most of the appropriate standards to be enforced without
imposition of an onerous bureaucracy: the schema. Any given instance of an XML document
must be capable of being validated against the appropriate schema. The schema
specification is in the process of replacing the Document Type Definition (DTD)
specification that has proven inadequate for this purpose.
We recommend that the appropriate database administrator or
data administration group develop XML schemas in concert with database definitions, and
then publish those schema on the company intranet or on the mainframe. Where important
data are stored in conventional file structures, XML schemas can be developed for these as
well. So long as both programming and operations can validate any given document at any
time, and do so on a regular basis, then the minimum set of standards enforcement is in
place for disciplined and productive results from XML usage. We recommend that XML be used
with enforced schema control or not at all. |
