[
Lists Home |
Date Index |
Thread Index
]
Per the SGML Handbook (Goldfarb, Clarendon Press Oxford, 1990):
pg 180:
"a public identifier is ... a unique non-system specific identifier
that can be converted to an actual storage identifier only by a table
lookup. The universe in which a public identifier is unique depends
upon whether it is a formal public identifier and upon its owner
identifier.
4.239 public identifier: a minimum literal that identifies public
text"
pg 378: "A public identifier is a name that is intended to be
meaningful across systems and different user environments. Typically
it will be a name that has a registered owner associated with it,
so that public identifiers will be guaranteed unique and no two
entities will have the same public identifier. This uniqueness can
only be achieved when the public identifiers are "formal public
identifiers" which is an optional feature that can be specified
in the SGML Declaration."
The next round of quibbling will be over whether or not a non-URI
identifier is of value, whether or not non-resolvable identifiers
are of value, and how to blame SGML. I'll save you some trouble:
1. No identifier is actually independent of a system of some
kind because an identifier without a system of identification
is just a syntax; in other words, the only provable property
is the spelling and structure, same as XML.
2. All a public identifier gets you is an identifier that is
mapped to the local storage system identifier (the system
identifier), but note, it is a mapping from one system of
identification to another.
3. URIs get around that by definition, though they in fact,
are the same thing. This is at the heart of the most non-resolvable
permathread on the web: is identity independent of identification
or what do the names of resources name. Note this thread nevers
impacts actual web operations; just their formal definitions in
systems that define these incompatibly (non-isomorphic operations:
systems are defined as data plus operations; an XML application
language is just syntax plus documentation without an accompanying
object model for implementation.)
But the nut of it is system independence: if you want your
names to be independent of the URI system (say the web), then
you need a means (a system) to map and a means (a system)
of registration to enable uniqueness. Think ISBN or VINs.
Yes, there are implementations that map PUBLIC identifiers to
web identifiers. For them that needs 'em, use 'em. OTW, not.
If you are using the web as your mass storage device, you
don't need public identifiers for much if anything although
they are still used in DOCTYPE declarations.
len
From: collin@seu.edu.cn [mailto:collin@seu.edu.cn]
...and what does the "public" indicate?
Thanks!
Collin
|
