# Re: Library Standards and URIs

Terry Allen (terry@ora.com)
Tue, 3 Jan 1995 13:09:19 PST

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    Message-Id: <199501032109.NAA21261@rock>

    From: Terry Allen <terry@ora.com>

    Date: Tue, 3 Jan 1995 13:09:19 PST

    In-Reply-To: Larry Masinter <masinter@parc.xerox.com>

    To: Larry Masinter <masinter@parc.xerox.com>, rdaniel@acl.lanl.gov

    Subject: Re: Library Standards and URIs

| We can't eliminate the chaos that already exists in the world of
| meta-data for documents; trying to invent a 'core' set doesn't reduce
| the chaos, in fact, but rather adds to it, by introducing yet another
| *new* attribute set.

Not chaos, but variability. Anyway,

| Naming each attribute *set* rather than each individual attribute will
| reduce the length to be something managable. It might be possible to
| also allow individual attributes to be named even if they don't occur
| in the overall set.
| <urc scheme="urn:iana:here.there.org:foo">
| <author>...</author>
| <title>...</title>
| <author scheme="urn:iana:banana.br:trigram">
| </author>
| </urc>

This example seems to mix one overall scheme (here...) with
a scheme local to an individual element (banana...). Wouldn't
it be better to offer instead only a choice of overall schemes,
on the assumption that the components are defined by the overall
scheme?

If that's to be done in SGML (which I am not advocating), schemes
with different URCs will have different allowable contents. It is
one of SGML's weaknesses that attributes can't affect content
models (you can't say in the DTD that <urc scheme="foo"> shall
contain only those elements allowed by scheme foo). So a better
approach (if SGML is really desired) would be to have one element
for each flavor of URC: urc.foo, urc.here, urc.banana. Then
in the DTD one could require that urc.foo have only the
desired content.

    --
    Terry Allen  (terry@ora.com)   O'Reilly & Associates, Inc.
    Editor, Digital Media Group    103A Morris St.
    			       Sebastopol, Calif., 95472
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