[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Again wit da AND and Repetitions / Singletons in a DTD
* Terje Norderhaug | | 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: | | (A,((B,C)|(C,B))) | (B,((A,C)|(C,A))) | (C,((A,B)|(B,A))) The number of states here more or less follows n factorial, leaving the solution useless after 10 elements in a list or so. | [...] This proves that supporting the AND connector isn't much | harder than implementing the current connectors. Given infinitely long paper tapes, yes. :) | 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. [...] This is essentially the same solution that John Cowan mentioned earlier, and that I mused might be extended to cover the {m,n} modifier as well. However, I now see a potential problem with this in the presence of ambiguous content models. I've taken a different line with this compared to many of the others here, since I see no reason not to allow them (they cause no harm in XML). Furthermore, the recommendation only has a non-binding requirement that they be rejected. (I will warn about them, but that's another matter.) The problem is that if you generate a non-deterministic automaton from the weaker content model (A | B | ...)* and convert it to a deterministic one your deterministic states will be combinations of the non-d ones, which (I think) may mean that in some cases you won't know whether to enable the special & actions or not, since you don't know whether you're inside the & group or outside it. Does anyone know whether this really is a problem or not? --Lars M. xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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