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

Date: Mon, 11 May 2009 20:47:37 +0100

Message-ID: <4A0880D9.7040503@deri.org>

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

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

Date: Mon, 11 May 2009 20:47:37 +0100

Message-ID: <4A0880D9.7040503@deri.org>

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

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

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 -- Dr. Axel Polleres Digital Enterprise Research Institute, National University of Ireland, Galway email: axel.polleres@deri.org url: http://www.polleres.net/Received on Monday, 11 May 2009 19:48:19 GMT

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