Number of active public XML schemas

[Ronald Bourret <rpbourret@rpbourret.com>]

I got an interesting question a couple of weeks ago -- roughly how many 
XML schemas are publicly available and actually being used?

I spent two evenings poking around the Web with a modem (not DSL), 
looking for schemas that at least appeared to be active. In that time, I 
found around 100 schemas that fit my criteria, which was simply that a 
date of 2003 or 2004 was somehow associated with the schema and that the 
schema appeared to be from some semi-reputable organization.

My research was primarily done by looking at  the XML Cover Pages [1], 
OASIS [2], xml.org [3], and Barry & Associates [4]. The Cover Pages have 
500+ schemas listed, but an awful lot of these seem to have died -- 
there was a flurry of intention from 1999-2001 that didn't produce much. 
xml.org had the same problem, although to a lesser extent, while Barry & 
Associates was somewhat better. OASIS was hard to get a read on; some 
projects looked real and some looked like nothing more than good intentions.

 From there, I went to Google and typed in <industry-name> xml, such as 
airline xml. This actually had surprisingly good results -- most areas 
turned up something of substance -- but was very slow going.

The interesting question, then, is how many vertical schemas are out 
there that are actually being used? Certainly the number 100 is a 
low-end figure, for several reasons:

1) I'm reasonably sure that at least 75% of the schemas I found are 
being used, probably more.

2) The definition of "schema" is very fuzzy. Many of the schemas I 
listed are actually multiple schemas, such as HL7, OTA, and the UK 
government. If you count these individually, you'll easily exceed 200 
schemas.

3) My search was far from complete. On the Cover Pages, I checked 
perhaps 30 schemas. On xml.org, I checked about 25%. And on Google, I 
checked less than 10 industry areas out of ~40 I could think of.

At this point, I'll take a wild guess and estimate that I found roughly 
1/4 to 1/2 of all active, publicly available industry schemas. The 
reason I'm so optimistic is that (a) so many of the Cover Page schemas 
were failures or pet projects that, even if still alive, aren't really 
being used, and (b) most industry searches aren't likely to turn up more 
than a few schemas. Note that this number does not include 
product-specific schemas or schemas used privately, of which I'm sure 
there are thousands.

You can look at the list of schemas I found at [5].

Comments?

-- Ron

[1] http://xml.coverpages.org/xml.html#applications
[2] http://www.oasis-open.org/home/index.php
[3] http://www.xml.org/xml/registry.jsp
[4] http://www.service-architecture.com/xml/articles/xml_vocabularies.html
[5] http://www.rpbourret.com/xml/VerticalSchemas.htm