Internal subset equivalent in new schema proposals?

James Tauber jtauber at
Wed Dec 2 03:16:43 GMT 1998

-----Original Message-----
From: roddey at <roddey at>

>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 Tauber / jtauber at /
Associate Researcher, Electronic Commerce Network
Curtin University of Technology, Perth, Western Australia

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