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   Re: [xml-dev] Re: Are the data users happy? Why not?

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K. Ari Krupnikov scripsit:

> John, the question is not "can I validate some string against *some
> criterion* because I have a tool that will?". The question is "can I
> validate some string wrt the use I intend to make of it".

No, it's "Can I cheaply and easily reduce the error rate in entered data"?
Full validation is beyond my powers, since I can't make my computer send
snail mail, still less process the replies.

> But how do you know it's *their* post code? Something tells me you are
> interested in the singleton set of *the user's* post code, not the
> larger set of *valid* post codes. Is a valid, but irrelevant, post
> code better for you than no post code at all or a bogus post code?
> 20502 is a valid US ZIP code. Do you want to send mail there that is
> addressed to me?

If you enter that, it's your problem.  But if you mean to type 10003 and
type 1003, I will not accept that (given country=US).

> Whose money you take is up to you. But after you take their money, you
> want to know where they are, don't you (although I'm not sure why)?

Partly because I get a cheaper rate from a credit card processor if the
address I supply matches the one associated with the card.
In addition, users don't get access without a signed contract, and I need
somewhere to tell Sales to send it.

> Presumably, you give your users a drop-down list and not a text field
> to reduce data-entry errors. As the list of enumerations grows longer,
> it becomes a greater potential source of errors than an unconstrained
> string because users can't be bothered to read through its entire
> length.

A valid point.  If more people knew their ISO 3166 country code, I would
allow them to type that and validate it on the fly.

> Validation, wither regexp- or set-based, only catches so many errors,
> while giving you the illusion that your data are somehow
> correct. 

No, while giving me the assurance that my data is not incorrect in easily
checkable ways.  It does not refer to a non-existent country (though it
could refer to the wrong country); it does not refer to an impossible
zip code (though it could refer to an unused or incorrect one).

John Cowan        http://www.ccil.org/~cowan          jcowan@reutershealth.com
Please leave your values        |       Check your assumptions.  In fact,
   at the front desk.           |          check your assumptions at the door.
     --sign in Paris hotel      |            --Cordelia Vorkosigan


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