[entity-resolution-comment] Re: uri vs. system confusion

[John Cowan <cowan@mercury.ccil.org>]

Mark Johnson scripsit:

> In working to develop a robust xml catalog system for Debian that's
> consistent with the OASIS XML Catalogs spec, I find that I'm still a
> bit confused about the distinction between the uri-based elements and
> the system-based elements.

In a word, the system-based elements are used only when an XML parser is
processing ENTITY and NOTATION declarations in the DTD.  The URI-based
elements are used for all other lookups.

> A. The <rewriteURI> example given in 4.3 implies that not only is the
>    prefix rewritten, but also that the intended document/entity is also
>    included in the 'rewritePrefix' attribute. Put another way, the
>    _complete_ URI is rewritten, and not just the prefix.

In that case, it so happens that the prefix is the same as the complete URI.
Any leading part of a URI can count as the prefix: you could rewrite
just "f" to "ht" in order to change all ftp: URIs to http: URIs, e.g.
Or as in this case you can rewrite the whole URI to a whole new URI.

> B. Given Paul Grosso's response (below) to a similar inquiry, another
>    implied usage is IMO that SYSTEM Ids get remapped _only_ via a
>    <rewriteSystem> element, and never via the <rewriteURI>
>    element. (This despite the fact that all system identifiers are
>    URIs.)
> 
>    Is this the intended usage? 

Yes.

>     [T]o remap the URI that
>     identifies a file within the current DocBook XSL stylesheet, I'd
>     want to use <rewriteSystem .../> to point to the local filesystem
>     like so:
> 
> <rewriteSystem 
>   systemIdStartString="http://docbook.sourceforge.net/release/xsl/current/";
>   rewritePrefix="file:///usr/share/sgml/docbook/stylesheet/xsl/nwalsh/"/>
> 
>     rather than using <rewriteURI.../>. But the text of the paragraph
>     implies that <rewriteURI.../> should be used. 

rewriteURI is the right thing, as follows from the principle above.

>     Does the reason for using <rewriteURI.../> have something to do with the
>     fact that the stylesheet URI does NOT appear in the XML document, and is
>     therefore not restricted by the ExternalID as SystemLiteral constraint
>     as per the XML spec? Again any clarification here would be greatly
>     appreciated...

Just so.

-- 
Do what you will,                       John Cowan
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