Re: [topicmaps-comment] referring to a topic from outside a TM

[Lars Marius Garshol <larsga@garshol.priv.no>]

* Thomas Bandholtz
| 
| ontopia.xtm should contain a namespace declaration.
| XTM DTD contains namespaces as fixed attributs -
| xmlns           CDATA     #FIXED 'http://www.topicmaps.org/xtm/1.0/'
| xmlns:xlink     CDATA     #FIXED 'http://www.w3.org/1999/xlink'
| xml:base        CDATA     #IMPLIED
| - but ontopia.xtm does not refer to this at all.

Huh? Here are lines 3-6 of ontopia.xtm:

    <topicMap
        id="ontopia-as"
        xmlns="http://www.topicmaps.org/xtm/1.0/"
        xmlns:xlink="http://www.w3.org/1999/xlink">

This contains namespace declarations for the default namespace, and
the 'xlink' namespace. What more do you want?

| - Secondly, http://www.topicmaps.org/xtm/1.0/ is a valid namespace
| name - but not a valid DTD location.

There's nothing wrong with it as the location of a DTD, but no DTD
happens to reside there. This does not in any way conflict with the
XML Namespace Recommendation. In that recommendation there is no
expectation that anything in particular be at the other end of the
namespace URI.

| BTW - is there a well defined, persistent location?

You can always find the DTD at:
  <URL: http://www.topicmaps.org/xtm/1.0/xtm1.dtd >
 
| Right. When you use XPointer like above you will have to maintain
| the named file and make sure it contains the named ID - what's the
| difference- The file just needs to contain _any_ element with
| whatsoever name that happens to have ID="topicmap" but containing
| "whatever  it chooses to".
| 
| Beeing bound to files is a legacy restriction. Topic Maps (even
| PS-collections) will be very large, so they will be maintained in
| databases, not in Gigabytes of XTM-files.

You are confusing things. There are five kinds of URIs involved in
topic maps:

  - those of subject indicators, also known as subject identifiers,
  - subject addresses,
  - source locators,
  - occurrence locators, and
  - variant locators.

Before you start talking about URIs in relation to topic maps you have
to figure out which kind you are talking about, and what you want to
do with it.

If you want to find the topic (if any) that has a particular URI as
one of its subject identifiers, then you look that up. If you store
the topic map in a relational database you just do a search for that
string in the SUBJECT_IDENTIFIER column. It's no harder than that, and
it's similar with the other kinds of URIs.

The fact that a topic has an HTTP URI does not mean that you cannot
ask a topic map engine based on a relational database: "please find
the topic that has this URI as its source locator".

-- 
Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
ISO SC34/WG3, OASIS GeoLang TC        <URL: http://www.garshol.priv.no >