Subject: Re: About XML to multiple language/multiple outputs From: Matthias Clasen <clasen@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> Date: Thu, 26 Aug 1999 21:49:15 +0200 |
> > > > > One can, perhaps, define both query and element rules on terms of an > > abstract query rule, not present in the language specification. > > > Actually, I believe (without having worked out all the details, of > course), that the existing query rule would be sufficient for this. > We know, for sure, that any other type of rule can be rewritten as a > query rule because the query rule allows node selection via an > arbitrary SDQL expression. The only potential problem is enforcing > the specificity rules that DSSSL requires. > I believe this can be done with the priority expression part of the > query rule by calculating a priority for each rule (thus, the basic > query rule itself would be translated into our "baseline" query rule, > so that we can alter the priority expression result). For instance, > we would automatically just add a large constant on to the result of a > query rule's priority expression, and we would calculate the priority > of an element rule based on the specificity of its gi or qualified-gi > argument. > The problem would, of course, come into play in that the user can > have their priority expression generate an arbitrarily large value, so > we could run into a problem where their value is so large that adding > anything on to it would cause an overflow. Of course, if they're > generating values that large, they're risking overflow, anyway, so > maybe it isn't as much of a concern. But, then, on the same note, > could we really decide what the constant would be that we would add to > query rule priorities, given that it has to insure that even a query > rule with a priority of 0 would outweigh any other rule? Picking an > arbitrary value for this would, essentially, put a cap on how specific > a qualified-gi in an element rule could be. However, such a > qualified-gi as might overflow such a limit is probably not a > practical reality, so, again, I wouldn't worry too much about it. > So, does anyone else think we need to move this discussion to a new > list: dsssl-guts? :) > I think a proper way to transform all rules into query rules without risking overflows would need a slight extension of the priority expression: Allow it to be a pair (or even list) of numbers, sort them lexicographically. Maybe that is the `abstract query rule' Avi was thinking of. -- Matthias Clasen, Tel. 0761/203-5606 Email: clasen@xxxxxxxxxxxxxxxxxxxxxxxxxx Mathematisches Institut, Albert-Ludwigs-Universitaet Freiburg DSSSList info and archive: http://www.mulberrytech.com/dsssl/dssslist
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