**From:** Asmus Freytag (*asmusf@ix.netcom.com*)

**Date:** Fri Sep 10 2010 - 19:00:21 CDT

**Previous message:**Michael D. Adams: "A simpler definition of the Bidi Algorithm"**In reply to:**Michael D. Adams: "A simpler definition of the Bidi Algorithm"**Next in thread:**Khaled Hosny: "Re: A simpler definition of the Bidi Algorithm"**Reply:**Khaled Hosny: "Re: A simpler definition of the Bidi Algorithm"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

The first discussions that lead to the current formulation of the bidi

algorithm easily go back 20 years by now. There's some value in not

re-stating a specification - even if a new formulation could be found to

be 100% equivalent. That value lies in the fact that any reader can

tell, by simple inspection, that the specification hasn't changed, and

that implementations that claim conformance to earlier versions of the

specification are indeed still conformant to later versions.

This point is particularly important for the bidi algorithm, because of

it's mandatory nature and the fact that it gets re-issued with a new

version number every time that the underlying Unicode standard gets a

new version (because of new characters added, etc).

That does not preclude other, equivalent formulations of the algorithm,

whether in text books or, perhaps, as technical Note. But the burden is

on the creators of these other formulations to show that their

supposedly easier or more didactic presentation is indeed equivalent.

Having said that, there are already two other formulations of the

algorithm that are proven to be equivalent to each other (and have not

proven to deviate from the written algorithm). I'm referring of course

to the C++ (http://www.unicode.org/Public/PROGRAMS/BidiReferenceCpp/)

and Java reference implementations.

A./

PS: Personally, I don't find the presentation in terms of the regular

expressions any more intuitive than the original.

**Next message:**Khaled Hosny: "Re: A simpler definition of the Bidi Algorithm"**Previous message:**Michael D. Adams: "A simpler definition of the Bidi Algorithm"**In reply to:**Michael D. Adams: "A simpler definition of the Bidi Algorithm"**Next in thread:**Khaled Hosny: "Re: A simpler definition of the Bidi Algorithm"**Reply:**Khaled Hosny: "Re: A simpler definition of the Bidi Algorithm"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]**Mail actions:**[ respond to this message ] [ mail a new topic ]

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