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

Re: What does "optional" mean?

  • From: Michael Kay <mike@saxonica.com>
  • To: xml-dev@lists.xml.org
  • Date: Sun, 26 Feb 2012 16:54:06 +0000

Re:  What does "optional" mean?
On 26/02/2012 14:11, Costello, Roger L. wrote:
> Hi Folks,
> Every schema language (DTD, XSD, RNG) has the notion of optional -- optional elements and optional attributes.
> But what does it mean to declare an element or attribute optional?
Go and read the relational database literature from the early 80s (?) 
when there was a religious war about the meaning of null, with Ted Codd 
and co writing papers advocating that there should be four or five 
different kinds of null with different meanings. Then when you've read 
them, chuck them in the bin.

Just as the attribute iubce='qwudob' means whatever the sender and 
recipient agree it should mean, so equally the absence of the iubce 
attribute means whatever the sender and recipient agree it to mean, 
which might be "I don't know", or "not applicable", or "I don't think 
you want to know this", or "you already know this so I'm not telling you 
again", or perhaps it means exactly the same as iubce='qwudob'.

Michael Kay

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index]


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.