The makeup of DEFINE.XML is described in a PDF document on the CDISC web site. It wasn't too hard to understand. From Mike's post it seems like XML is quite unknown to him. I can tell you that XML is the easy part. Knowing your specific standard is where the complexity comes in.
XML is just a way to mark up data. You surround it with tags that you make up. Like this.
John Leveille
d-Wise Technologies, Inc.
So, since XML is markup using any tag names you like -- how can it be useful? Well, it becomes useful when someone makes a standard that we all try to use. That is precisely what CDISC is doing for the Pharma community.
So, there is this standard that CDISC has come up with called SDTM - Study Data Tabulation Model. The grand idea is that if we all put our study data into SDTM XML formatted files, then we can have a file called DEFINE.XML that basically provides a manifest of all the tables in columns in the study -- then we should be able to exchange data between lots of different companies and software systems.
The reality is far from this utopic vision, but that is where the CDISC organization wants to help us go.
I think Mike points out an interesting fact. Smaller organizations don't have the inertia of big pharma. So many times they just decide that it is both easiest and cheapest to come up with the most expeditious, albeit proprietary, data transfer mechanism. It is within the larger Pharma where the motivation is higher to embrace the standard in an effort to save money and rework.