- From: Dan Connolly <connolly@w3.org>
- Date: Thu, 15 Jul 2004 15:00:09 -0500
- To: Jim Hendler <hendler@cs.umd.edu>
- Cc: public-rdf-dawg@w3.org
On Thu, 2004-07-15 at 13:14, Jim Hendler wrote: > At 7:54 -0700 7/15/04, Dan Connolly wrote: > >While thinking about xquery-based designs, I realized I have been > >assuming the following requirement. What do other folks think? > > > >3.X Limited complexity > > > >Less expressive languages are easier to implement, deploy, secure, > >and optimize (cf the Principle of Least Poser in an essay on design > >principles for the Web[1]). Since a large and interesting class of > >applications can be addressed with query languages that are less > >expressive than programming languages, this design should not > >involve a turning-complete query evaluator. The halting problem must > >not be expressible in this query language design. > > > >[1] http://www.w3.org/DesignIssues/Principles > > Dan - while I agree with the goal of this, I'm not sure the wording > is correct - that is, I don't think what you're after has to do w/the > ability to express the halting problem, and I suspect that given that > RDF graphs, being actually "pseudo graphs" (since they can have > multiple links between same nodes) and allowing cycles, it is > possible to express queries even in simple languages that could have > halting issues - remember that decidability is in the problem, not in > the language used to express it hmm... I meant to say "without using optional extensions" or something, but maybe that doesn't cut it either... > (I can give you trivial problems that > are undecidable, for example stacking one block on another when each > block has a separate controller) -- I think if we simply drop the > last sentence it is closer to what you actually want to say (Turing > completeness is in the language, decidability/halting is in the > problem) so "yes" to: > > 3.X Limited complexity > > Less expressive languages are easier to implement, deploy, secure, > and optimize (cf the Principle of Least Poser in an essay on design > principles for the Web[1]). Since a large and interesting class of > applications can be addressed with query languages that are less > expressive than programming languages, this design should not involve > a turning-complete query evaluator. Well, that's only should-strong. A design like javascript or XSLT would pass it, if there's some justification for going turing-complete. hmm.. "... must not involved a turing-complete query evaluator"? > -JH > p.s. Sorry, going on 20 years as a Professor of Computer Science has > made me overly literal on these things. -- Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 15 July 2004 16:00:20 UTC