[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message]

RE: Are people really using Identity constraints specified in

RE:  Are people really using Identity constraints specified in
Michael Kay wrote:

> I tend to be a little wary of constraints myself. 
> Many of those you see in student textbooks are 
> misguided. If I see a schema (XML or RDB) with the
> constraint that employees must be over 16, I ask 
> myself what the IT department would do if the 
> business decided to hire someone under 16. If
> there's a rule that an employee's manager must 
> themselves be an employee, I ask what would 
> happen when someone is told that they now report 
> to a contractor. 

This is excellent:

> It's not the job of computers to limit what people 
> are allowed to do (or the job of the IT department 
> to regulate the business). 

The following innocuous sentence has profound implications  
on the role of schemas:

> A guideline I use is that constraints should be there 
> only to protect the IT system itself from data that 
> it cannot handle.

Would you elaborate upon this sentence Michael?  I believe
that you are saying that the role of a schema is to define
things such as:
- ensure that a "date" is indeed a valid date
- ensure that an "age" is indeed a valid age

The role of a schema is not, for example, to specify:
- the "age" must be at least 16.

So, your guideline says: use schemas to specify datatypes
for objects, not their range of values.  Is that a fair
summary of your guideline?  /Roger


Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced!

Buy Stylus Studio Now

Download The World's Best XML IDE!

Accelerate XML development with our award-winning XML IDE - Download a free trial today!

Don't miss another message! Subscribe to this list today.
First Name
Last Name
Subscribe in XML format
RSS 2.0
Atom 0.3

Stylus Studio has published XML-DEV in RSS and ATOM formats, enabling users to easily subcribe to the list from their preferred news reader application.

Stylus Studio Sponsored Links are added links designed to provide related and additional information to the visitors of this website. they were not included by the author in the initial post. To view the content without the Sponsor Links please click here.

Site Map | Privacy Policy | Terms of Use | Trademarks
Free Stylus Studio XML Training:
W3C Member
Stylus Studio® and DataDirect XQuery ™are products from DataDirect Technologies, is a registered trademark of Progress Software Corporation, in the U.S. and other countries. © 2004-2013 All Rights Reserved.