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   Re: XLink - Assert linking relationships among more than two resource s

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  • From: "KenNorth" <KenNorth@email.msn.com>
  • To: "Hien Luu" <Hien@Icarian.com>, "Eve L. Maler" <elm@east.sun.com>
  • Date: Thu, 2 Mar 2000 16:17:07 -0800

Hien Luu wrote;
> >I am looking for a way to maintain referential integrity between two
> >different XML files.

Eve L. Maler wrote:
> Here is an example of a simple link that (by definition) contains the

Perhaps Hien was asking about "referential integrity" in the database
context, which means more than asserting a linking relationship. The
relationship, and rules about the relationship, are defined to a container
(database) that blocks actions that would subvert data integrity. For
example, you might have a conference hotel scenario involving parent-child

Conf  ->      Hotel    ->             ImageURL
-------          ------                     -------
Perl Two     Marriott         www.javaone.com/hotels/marriott.jpg
                   St. Francis     www.javaone.com/hotels/stfrancis.jpg
                   AveryE          www.javaone.com/hotels/averye.jpg

You define a rule to cascade deletions between Hotel and ImageURL. If the
AveryE burns down, you delete the parent from the Hotel list and the
database engine cascades the deletion to the child (ImageURL == averye.jpg).

For the Conference -> Hotel link, you define a different rule. The example
data below illustrates why you do not want to cascade deletions from
Conference to Hotel if a conference is cancelled.

Conf  ->      Hotel    ->             ImageURL
-------          ------                     -------
Java One     Marriott         www.javaone.com/hotels/marriott.jpg
Perl Two     Marriott         www.javaone.com/hotels/marriott.jpg

Given a database scenario, the developer:
- defines the relationships
- declares the appropriate constraints
- relies on the container to maintain referential integrity.

I interpreted Hien's inquiry to be "How do I do this if I have two XML files
instead of container-enforced referential integrity? Does XLink provide a

================== Ken North =============================
See you at Java Developer Conference (London, March 13-15, 2000)
XML One (Austin, March 29-31, 2000) www.xmlconference.com

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