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"If the system identifier is a URN in the publicid namespace, it is converted into a public identifier by "unwrapping" the URN. In this = case, one of the following must apply: 1. No public identifier was provided. Resolution continues as if the = public identifier constructed by unwrapping the URN was supplied as the = original public identifier and no system identifier was provided. 2. The normalized public identifier provided is lexically identical to = the public identifier constructed by unwrapping the URN. Resolution = continues as if the system identifier had not been supplied. 3. The normalized public identifier provided is different from the = public identifier constructed by unwrapping the URN. This is an error. = Applications may recover from this error by discarding the system identifier and proceeding with the original public identifier." So the following DOCTYPE declaration should amount to not specifying a system identifier: <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" "urn:publicid:-:OASIS:DTD+DocBook+XML+V4.1.2:EN"> BTW, early drafts of the XML Catalog spec suggested that XML Catalog resolvers should be expected to look after a default catalog, located = as a relative URI to the document being processed [2]. This was removed = because, as Daniel Veillard states it [3], "... having to make an URI reference lookup based on the resource one want to fetch to guess if there is a catalog associated is not scalable, not secure and not something I ever = want to implement. At least I can trust /etc/xml/catalog and load it once = for the full lifetime of my application."=20 My conclusion: If you must rely on resolving entities via canonical = URLs over the internet, you are in for all kinds of trouble. Better take the trouble to set up local entity resolution. [1] http://www.oasis-open.org/committees/entity/specs/cs-entity-xml-catalogs= -1.0 .html#s.ext.input [2] https://lists.dulug.duke.edu/pipermail/lsb-xml-sgml/2002-August/000265.h= tml [3] https://lists.dulug.duke.edu/pipermail/lsb-xml-sgml/2002-August/000266.h= tml kind regards --=20 \|/ <@ @> Peter Ring +-oOO-(_)-OOo--------------------------- | Address Pal=E6gade 4 | P.O.Box 9026 | DK-1022 K=F8benhavn K | Phone +45 3396 0153 | Fax +45 3396 0101 | EMail pri@magnus.dk | WWW www.magnus.dk -----Original Message----- From: Oliver Fischer [mailto:plexus@snafu.de] Sent: 6. maj 2003 21:26 To: Jirka Kosek Cc: Peter Ring; docbook@lists.oasis-open.org Subject: Re: [docbook] URN for Simplified DocBook and DocBook XML Jirka Kosek wrote: > Using URN is a very good practise in many places (e.g. namespace=20 > identifiers) but not in system identifiers. System identifier must be = > always resolvable, and this can't be guaranteed with URN. According to the standard is a URN also a valid URI - IMHO. Or did I=20 misinterpret the docs I read? A SystemLiteral is URI and both URL=20 and URN are URIs. So why not use a URN als SystemLiteral? I could use catalog files to resolve the URN. Or not? MfG --=20 Oliver Fischer --[ Oliver Fischer ]-[ plexus@snafu.de ]--------------------------- Technologie des letzten Jahrtausends? Das Internet! http://www.xshare.com
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