[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: How did "public identifier" get its name...
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@s... [mailto:collin@s...] ...and what does the "public" indicate? Thanks! Collin
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