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

Re: ID/IDREF is evil

  • From: Michael Sokolov <msokolov@safaribooksonline.com>
  • To: "Costello, Roger L." <costello@mitre.org>, "xml-dev@l..." <xml-dev@l...>
  • Date: Mon, 03 Feb 2014 17:23:00 -0500

Re:  ID/IDREF is evil
I thought ID/IDREF was about expressing the integrity of links (IDREF must have a matching ID), not about context-sensitivity, but then again I never used it since my links were always to different documents, and it seemed useless (rather than evil) so I could be wrong.


-Mike

On 02/03/2014 05:05 PM, Costello, Roger L. wrote:
Hi Folks,

In this message I will attempt to persuade you:

1. Do not use the ID/IDREF capability.

2. Use a layering approach:

	(a) Layer 1: express your XML as a context-free grammar.

	(b) Layer 2: express context-sensitive rules using Schematron.

3. The ID/IDREF capability is a context-sensitive rule.

Now for my argument:

First, let me persuade you that by using ID/IDREF you have introduced context-sensitive rules into your XML. Consider this XML, which does not use ID/IDREF:

<Book>
       <Title>Principles of Programming</Title>
       <Author>M. A. Jackson</Author>
</Book>

To show XML's rule nature, let's express it like so:

Book 	--> Title Author
Title 	--> string
Author 	--> string

That's a context-free grammar.

Now let's add an ID/IDREF:

<Book seller="Amazon">
       <Title>Principles of Programming</Title>
       <Author>M. A. Jackson</Author>
</Book>

Assume that @seller is of type IDREF. I don't show the corresponding ID attribute.

Let's express that XML using grammar rules. The rule for the Book element depends on the existence of a corresponding ID attribute; if there is none, the Book rule is invalid. So we may express Book's rule like so:

Book Amazon --> Title Author

Read that as:
	
	In the context of an Amazon symbol
	the Book element may be replaced
	by Title and Author.

In other words, our grammar tells us that this a valid string

	Principles of Programming M. A. Jackson

only if the symbol "Amazon" exists.

See the context-sensitivity? Book is context-sensitive due to the ID/IDREF.

Any time you use ID/IDREF in your XML document you have introduced a context-sensitive rule into your XML document.

"So what?" you ask.

Well, here's so what:
	
	All known parsing algorithms for context-sensitive
	grammars are either very inefficient or very complex.

	Reasoning about context-sensitive grammars is difficult.

	Proofs about context-sensitive grammars is difficult.

	Take cue from compiler developers: they separate
	context-sensitive processing into a separate pass.

So don't use ID/IDREF.

Of course, that doesn't mean you will never have data that has intra-data dependencies. What it means is that you should modularize your grammar rules: express your context-free rules in your XML document and express your context-sensitive rules (intra-data dependencies) in Schematron. That's a nice, clean separation-of-concerns. That's a modular data design.

Let's recap:

1. ID/IDREF introduces context-sensitive rules into your XML grammar wherever there is an ID attribute and wherever there is an IDREF attribute.

2. Don't use ID/IDREF.

3. Modularize your rules: express context-free rules in XML and express context-sensitive rules in Schematron.

Comments?

/Roger

_______________________________________________________________________

XML-DEV is a publicly archived, unmoderated list hosted by OASIS
to support XML implementation and development. To minimize
spam in the archives, you must subscribe before posting.

[Un]Subscribe/change address: http://www.oasis-open.org/mlmanage/
Or unsubscribe: xml-dev-unsubscribe@lists.xml.org
subscribe: xml-dev-subscribe@lists.xml.org
List archive: http://lists.xml.org/archives/xml-dev/
List Guidelines: http://www.oasis-open.org/maillists/guidelines.php






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


PURCHASE STYLUS STUDIO ONLINE TODAY!

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.
Email
First Name
Last Name
Company
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.