On 3/5/2012 8:52 PM, Paul Tyson wrote:
> But beyond formal definitions, the "meaning" of URIs (like the "meaning"
> of words) is established through deliberate and consistent use by
> members of the community that agrees to use them. There are no
> "accidental" URIs--every one is placed by some person for some
> particular purpose. (01)
Yes. But please note the conditions. Even when the developers
follow the W3C recommendations in every detail, they cannot escape
the fundamental principles of logic. Following is a copy of the
conditions, which are typical of the kinds of systems that people
need to make interoperable: (02)
> Base vocabulary V: A collection of terms defined precisely at a level
> of detail sufficient for interpreting messages that use those terms
> in a general context C.
> System A: A computational system that imports vocabulary V and uses
> the definitions designated by the URIs. But it uses the terms in
> a context C' that adds further information that is consistent with C.
> That info may be implicit in declarative or procedural statements.
> System B: Another computational system that imports and uses terms
> in V. B was developed independently of A. It may use terms in V
> in a context C'' that is consistent with the general context C,
> but possibly inconsistent with the context C' of System A.
> Problem: During operations, Systems A and B send messages from
> one to the other that use only the vocabulary defined in V.
> But the "same" message, which is consistent with the general
> context C, may have inconsistent implications in the more
> specialized contexts C' and C''. (03)
This example uses the URIs and definitions in *exactly* the way
the W3C recommends. But if systems A and B use those common terms
in contexts with independently developed detail, the "same" message
can have inconsistent implications in the two systems. (04)
> If the purpose fails or goes amiss, someone must
> take corrective action. The price of effective communication--with or
> without URIs--is eternal vigilance, not rigid definitions. URIs lower
> the price of effective communication because of the ease with which
> their use can be monitored and corrected. (05)
Everybody agrees that globally unique IDs are useful. But they are not
magic. People in every technical field have recognized the need for
standardized identifiers with precise definitions for over a century.
They have discovered the problems I mentioned above in their fields.
If you can't solve local problems with locally unique identifiers,
you won't solve them with globally unique IDs. (06)
If you don't see the problem, please study the above example and think
about it. URIs, by themselves, cannot solve that problem. Much more
is needed, and it involves version control and other constraints
and/or conventions. (07)
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