Subject: Re: About Constructions rules From: Brandon Ibach <bibach@xxxxxxxxxxxxxx> Date: Thu, 15 Jul 1999 16:08:50 -0500 |
Quoting Avi Kivity <Avi@xxxxxxxxxxxxx>: > On Thursday, July 15, 1999 23:31, Chris Maden [SMTP:crism@xxxxxxxxxxx] > wrote: > [query construction rules] > > > > But of course, you have to check every node against your list of > > queries. With only element construction rules, a very small > > percentage of all nodes (usually) are candidates for a given > > construction rule. Evaluating every node will hose your performance. > > You can compile queries, of course, but with arbitrary possible > > expressions, you'll always have potential ratholes. > > > I don't see why. The standard says: > > [...] > > This means that the rule is called, at most, once per grove per mode. If any > thrashing about is to be done, you have to specify it explicitly. And of > course it can be done lazily. > Yes, the query is executed just once to generate the "target" node list, but Chris is right is saying that *every* node in the grove would have to be tested against it. That's every single character, every attribute assignment, etc. This brings up the problem of calling Jade's bluff on the "each character is a separate node" trick. Still, given that node lists are opaque (meaning that the processor can represent them however it wants to), it should be possible to implement the checks for node membership relatively efficiently. For instance, a smart processor should be able to figure out if a query expression would exclude character nodes entirely, and thus it wouldn't even have to check them. This is, of course, a very simplistic example, but you can see the possibilities. In short, I think Chris has a legitimate concern, but that it can be addressed without extreme difficulty (using methods that are probably already being used elsewhere in Jade). -Brandon :) DSSSList info and archive: http://www.mulberrytech.com/dsssl/dssslist
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