Again wit da AND and Repetitions / Singletons in a DTD

Terje Norderhaug terje at
Tue May 18 04:25:38 BST 1999

At 11:50 AM 5/17/99, roddey at wrote:
>>>But I guess the & syntax from SGML is deceptively simple.  I don't
>>>completely follow that other thread, but I gather it's hard to implement
>>>which is probably why they left it out of XML.
>>No, it is not particularly hard to implement support for the AND connector
>>in a validating parser. However, the AND connector is redundant, as one can
>>express the same using the other connectors (although not very elegant).
>>For example, take the content model (A & B & C) expressing that we require
>>the three elements in any order. Here is the XML equivalent content model:
>  [snip]
>>However, there are better ways of implementing support for AND connectors
>>than to convert AND content model into such tree structures. Simply make
>>the parser keep track of which elements in the AND list have not yet been
>>parsed. For each element encountered, remove its item from the list. Signal
>>an error if the parser encounter an element not in the list of remainders,
>>unless all of the remainding elements in the list are optional. Repeat
>>until the list is empty or a parsed element is not in the list and all
>>remainders are optional.
>But that ignores the issue of what happens when an AND connector is embedded
>deeply with some very complex content model that is otherwise totally a
>XML type DFA! Do you then give up on doing a DFA for the entire content model
>when that happens? If not, then how do you do it? If you do, then its not
>terribly simple to do and its definitely not terribly quick. This gets back to
>my original question of how to deal with AND.

Please provide an example of such a complex content model that includes use
of AND, simplified as much as possible while still demonstrating your

-- Terje <Terje at> | Media Design in*Progress

   Software for Mac Web Professionals at <>
   Take advantage of XML with Emile, the first XML editor for Mac.

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