RE: How are approxMatch matching rules declared?

["Steven Legg" <steven.legg@adacel.com.au>]

Hallvard,

Hallvard B Furuseth wrote:
> [Models] 4.1.2 (Attribute Types) has no
>     ["APPROX" SP oid]
> part which can be used to declare the matching rule which
> approxMatch filters on the attribute should use.

That's because there are practically no matching rules defined
which describe approximate matching semantics. For the most
part, if such a field were defined there would be nothing with
which to populate it. The semantics of an approximate match
filter item have always been left to the discretion of the
server implementations.

> Should that be
> fixed?  Or must an implementation which wants to use implement
> approxMatch define a syntax like
>     ["X-APPROX" SP oid]		; approxMatch matching rule
> or do something like defining an implicit approx matching rule for
> each syntax which supports approxMatch filters?

In principle, every attribute type with an equality matching rule
supports approximate matching though in practice it might not differ
from the equality match.

> Should [Models] say something about this?

More likely the protocol draft since that is where the search operation
is described.

Regards,
Steven