Re: Hashing, and Ted's concerns about wastefulness

At 15:16 02/02/99 -0800, Bill Newman wrote:
>Ted wrote (quoting Graham)
>
>> Yes, but we need to specify exactly how that is represented.  Remember
>> that most hashes on files care about every bit of whitespace and every
>> control character; if we don't specify the representation very well,
>> we will end up with conflicting hashes on equivalent feature expressions.
>
>How bad a problem is this? Is it is worth trying to assign the same
>hash values to differently-represented-but-ultimately-equivalent
>feature sets? It is a feature, but it adds complexity to the
>specification and to each implementation.

Good question.

I don't have a clear answer, but I *suspect* that
"differently-represented-but-ultimately-equivalent feature sets" won't be a
big issue.  I have an unsubstantiated view that automatically recognizing
the same feature set from different authors will not be a big requirement.

>Do you anticipate a pattern of usage where this feature would 
>significantly increase efficiency?

Personally, no.

Also, even if we did not require the hash to be computed over a fully
canonicalized value, a combination of whitespace normalization and
presentation conventions might still match a good number of separately
authored cases.

One thing I do strongly believe:  this matter does not impact correct
functioning of the system (to the extent that appropriate dereferencing
mechanisms exist);  rather, it reates to possible efficiency of operation.

#g

------------
Graham Klyne
([email protected])