From: Jos de Bruijn <debruijn@inf.unibz.it>

Date: Tue, 12 May 2009 11:08:14 +0200

Message-ID: <4A093C7E.6040307@inf.unibz.it>

To: Axel Polleres <axel.polleres@deri.org>

CC: RIF <public-rif-wg@w3.org>

Date: Tue, 12 May 2009 11:08:14 +0200

Message-ID: <4A093C7E.6040307@inf.unibz.it>

To: Axel Polleres <axel.polleres@deri.org>

CC: RIF <public-rif-wg@w3.org>

I believe this works. Basically, you define the functions only for those cases you are sure that F&O defines them. I think I like this solution better than what I proposed below. As for the xs:decimal casting function: you could follow the same logic and include in the domain of the function only those values such that the result of casting to xs:decimal requires only 16 decimals. Analogous for the other casting functions coming from F&O. Best, Jos Axel Polleres wrote: > Please check, wheter the following reformulation of the Section 3.5 of DTB > http://www.w3.org/2005/rules/wiki/DTB#Numeric_Functions > > works for resolving the issue on numeric functions. > > Axel (apologies for late edits) > > Jos de Bruijn wrote: >> XPath functions and operators essentially says that each implementation >> can decide for itself which length for decimals it supports. For >> example, implementation A could support decimals of length 16, while >> implementation B supports decimals of length 20. In addition, each >> implementation can use its own rounding algorithm for representing >> numbers that need larger decimals. For example, implementation A could >> truncate numbers, while implementation B rounds them. >> >> this poses problems for us when defining things like casting functions >> and arithmetic operations. >> for example, according to XPath casting a string >> "0.1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111" >> >> to a decimal results either in an error or a decimal of some length >> (given by the implementation) that is obtained from the number >> corresponding to the string by some arbitrary rounding algorithm. >> >> It is not possible for us to define this kind of behavior in DTB, >> because functions are defined as functions: you have some input values >> that define an output value. >> In addition, it is really bad for interchange, since some >> implementations do something, while other implementations do something >> else, and you get no warning. >> So, for casting, I propose to define the xs:decimal casting function >> such that the result of casting a string to a decimal is simply the >> number with the input string as lexical representation, and so we have >> no exception behavior. >> >> We might define conformance such that implementations only need to >> support decimals of a particular length. >> >> >> The problem with numeric functions are similar. With addition, >> subtraction, and multiplication we run into the same problem. Again, I >> propose to define the functions such that the output values are simply >> the decimals which are the result of the arithmetic operations and not >> from some implementation-dependent modification. >> With division it gets a bit more complicated. For example, there is no >> decimal that can represent the result of dividing 1 by 3, because there >> are no infinite-length decimals. If we had owl:real we could still >> properly defined the division function, although there is no syntactical >> representation for the result. I have two possible solutions for you: >> (1) We reintroduce owl:real and use it for the definition of >> numeric-divide (I think we need it only there). >> (2) We define the domain of numeric-divide such that only pairs of >> numbers a,b (if they are decimals) are included if a/b can be >> represented using a decimal. This means that if 1,3 are the arguments, >> the value of the function is not specified by DTB and is left up to the >> implementation. >> >> I think these are crucial issues and we need to have at least an idea of >> where we want to go before DTB can go to last call. Otherwise, it will >> not be possible to make any RIF implementations. >> >> >> Best, Jos > > -- +43 1 58801 18470 debruijn@inf.unibz.it Jos de Bruijn, http://www.debruijn.net/ ---------------------------------------------- Many would be cowards if they had courage enough. - Thomas FullerReceived on Tuesday, 12 May 2009 09:09:07 UTC

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