Re: REL and REV attributes (Was: More comments on HTML 3.0)

Craig Hubley (
Wed, 26 Apr 95 05:18:46 EDT

> Bert Bos <> writes:
> > Paul Burchard <> writes:
> > |Bert Bos <> writes:
> > |> I still don't see why we need both REL and REV. They have
> > |> exactly the same meaning.
> > |(I assume you meant, exactly the _opposite_ meaning.)
> > No, I mean the *same*.
> That's wrong. A non-symmetric relation is *not* equal to its
> reverse relation. And most of these relations are non-symmetric.

Agreed. Most are non-symmetric, and even when symmetric it is not
clear that Parent=Reverse(Child) unless this constraint/rule/axiom
is stated somewhere...

> Using ad hoc word association to describe a precise mathematical
> operation is a bad idea. That's exactly what I don't want to see.

I think authors are often specifying an association not a precise operation.
What if you have descriptions of two people, one the parent of the other ?
Then child/parent has a different semantics altogether, not the expected...
and I don't want to see a constraint language creeping into HTML this way.
But I'm willing to acknowledge the value of AND/OR/NOT/REVERSE relationships.

Meanwhile, bear in mind that 25 years of hypertext research has proven
the value of naming links with simple strings determined by the author,
with NO semantics assumed by the basic (non-application-specific) software.
Building a formal type system on the strings is not necessarily as widely
accepted a practice or skill. In hypertext systems that tried to do this,
like Xerox NoteCards, users usually fell back to 'ad hoc word association'

> Drop REV, but add general relational operators to the syntax
> of REL. E.g., REL="Reverse(Child)" in place of REV="Parent",
> and REL="Join(Glossary,Author)" to refer to the author of the

Are you classifying the link, or what one finds at the other end ? This
seems like the same thing, until one carefully considers this terminology.
I had understood that REL/REV were primarily to define the relationship.

In what sense can Document B be the 'Join(Glossary,Author)' of Document A?
I can see how Document B might be the 'Glossary AND Index' of Document A...
or how Document A might be 'GlossarIED AND IndexED' by Document B...
(whatever precise mathematical language might be used to express that...
as a recovering mathematician I would accept the 'ED' suffix approach...

> document's glossary. (Any standard relational notation we
> should use?)

If you are typing a link,

If we're going to have two attributes, I'd rather see one qualitatively
state the relationship (REL) and another, a quantity/scalar, state the
strength of the relationship (0.9, 1.0, -1 for NOT, 1/x for INVERSE?)
Oops I fell off the mathematical wagon!

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