Subject: Re: [xsl] except (was: Keys with duplicates should be simple) From: Dimitre Novatchev <dnovatchev@xxxxxxxxx> Date: Sun, 2 Feb 2014 21:46:36 -0800 |
I have both graduate-level mathematics education and not extremely-bad English. I have never found any problems with the name of the XPath 2.0 operator "except". The name clearly conveys the semantics -- both to non- mathematicians and to people with mathematics background. Also, it is a notable achievement that the WGs involved in producing the XPath 2.0 and the F &O W3C specifications, found a good *single* word for what mathematicians express using a 2-word phrase. The main thing to remember when using the operators "union", "intersect" and "except" is that they are set operators and cannot be applied on arbitrary sequences -- such that contain one or more atomic items. Of course, it would be unrealistic to expect that the names could also convey the set-based semantics, without becoming much longer and confusing to the non-mathematician. On Sun, Feb 2, 2014 at 1:04 PM, Michael Kay <mike@xxxxxxxxxxxx> wrote: > >> >> So while I agree with you on the whole, I also make an exception for >> 'except'. It just isn't that bad. Indeed, there is an entire >> profession of people (I think they're called 'mathematicians') who >> consider such verbal stunt work to be just a day at the office. >> > > Indeed, I'm a little curious as to why "except" causes problems. I think we chose "except" rather than "difference" because "except" would be more meaningful to non-mathematicians. > > We often get people on XSLT forums who are sufficiently unfamiliar with boolean logic that they use "and" and "or" incorrectly. For example, they will use "and" to mean "union", as in > > select="para and section" > > which is natural enough if you understand English and don't understand maths. I don't think it would have been prudent to design a language in which "and" meant "union". So in general, maths is a better guide to these operators than English. > > But as for "except", it seems very natural to me: > > select="* except para" > > seems to reflect normal English usage, such as "all vehicles except bicycles". (Allowing plurals would make it more readable, but that's asking a bit much...) > > Perhaps you are reading "except" as "that are not", i.e. a negated predicate rather than a set difference). In English this reading would often work, as in "all vehicles that are not bicycles". But in English grammar, what follows "except" is not a predicate that qualifies what precedes it: you cannot say "all vehicles except blue". So I think the XPath usage is aligned with English usage in this instance. > > I'm not sure I followed the thread carefully enough, but I think the usability problem in this case was not in fact the "except" operator, but rather the use of "para" to mean "child::para" rather than "self::para". That's probably an inevitable price you have to pay for conciseness: wherever you allow defaults, they will sometimes be wrong. > > Michael Kay > Saxonica > -- Cheers, Dimitre Novatchev --------------------------------------- Truly great madness cannot be achieved without significant intelligence. --------------------------------------- To invent, you need a good imagination and a pile of junk ------------------------------------- Never fight an inanimate object ------------------------------------- To avoid situations in which you might make mistakes may be the biggest mistake of all ------------------------------------ Quality means doing it right when no one is looking. ------------------------------------- You've achieved success in your field when you don't know whether what you're doing is work or play ------------------------------------- To achieve the impossible dream, try going to sleep. ------------------------------------- Facts do not cease to exist because they are ignored. ------------------------------------- Typing monkeys will write all Shakespeare's works in 200yrs.Will they write all patents, too? :) ------------------------------------- I finally figured out the only reason to be alive is to enjoy it.
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