>How can you represent a strictly acyclic graph using ID/IDREF? For
>instance, if you have an employee list, and every employee has an ID
>attribute which is his/her employee number and an IDREF attribute which
>refers to his/her manager, what do you do when you reach Le Gran Fromage
>(sp?)? This person has no manager, but the parser will consider it an error
>if his/her manager field does not refer to someone else's employee id.
You could just make the IDREF attribute #IMPLIED:
<!ATTLIST employee
id ID #REQUIRED
manager IDREF #IMPLIED
>
James
-- James Tauber / jtauber@jtauber.com / www.jtauber.com Associate Researcher, Electronic Commerce Network Curtin University of Technology, Perth, Western AustraliaMaintainer of : www.xmlinfo.com, www.xmlsoftware.com and www.schema.net