- From: Jeen Broekstra <jeen.broekstra@gmail.com>
- Date: Wed, 30 Mar 2011 08:43:31 +1300
- To: Axel Polleres <axel.polleres@deri.org>
- CC: public-rdf-dawg-comments@w3.org
On 29/03/2011 22:09, Axel Polleres wrote: > thanks for your thorough and helpful feedback. > > This addresses your comment on NOT EXISTS vs. MINUS [1] which you > later refined in [2]. Your other comments on aggregates in [2] will > be answered in a separate mail. > > Essentially, it seems your concern boils down to the following > paragraph of your mail: > >> This leaves us with two scenarios: >> >> 1. the two patterns share a variable, in this case the MINUS can >> be replaced with a NOT EXISTS; 2. the two patterns do not share a >> variable, in this case the MINUS can be ignored. >> >> All in all it seems to me that MINUS as currently defined does not >> add additional expressivity to the language and is only a syntactic >> variant. > > Let me first emphasize that the reason we have two negation forms is > because it reflects two ways of thinking about negation. it's not > expressivity in the technical sense, it's more about how people > think about it and this has eventually evolved into two proposals in > the group which have different syntax. Fair enough. Note that I am not objecting to having something that is "merely" a syntactic variant. My comment was more motivated by confusion about whether or not this was the intent. Thanks for clarifying. > Next, find an example where MINUS and NOT EXISTS are actually > different, despite variables are shared. The differences in this > example are based on NOT EXISTS relying on the variable substitution > that happens during filter function evaluation: [snip good example] > Hope this helps for clarification. We'd appreciate if you could > indicate whether this response adequately addresses your comment. It does. Thanks for taking the time and for providing not one but two good counter-examples. I may have to run my implementations through a few extra testcases to see if I've got it right :) Best regards, Jeen
Received on Tuesday, 29 March 2011 19:44:10 UTC