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Re: redefining a namespace prefix and Base IRI definition

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 26 Sep 2005 09:38:49 +0100
Message-ID: <4337B399.5070106@hp.com>
To: Eric Prud'hommeaux <eric@w3.org>
CC: public-rdf-dawg@w3.org



Eric Prud'hommeaux wrote:
> We have two shorthand syntaxes for building URIs: qnames and relative
> URIs. These two are intertwined in rw23:
> [[
> [A]
> SPARQL provides an abbreviation mechanism for IRIs. Prefixes can be
> defined and a QName-like syntax [NAMESPACE] provides shorter
> forms. Prefixes may be used anywhere after they are declared;
> redefining a prefix causes the new definition to be used from that
> point in the query syntax. The base IRI for the resolution of relative
> IRIs may be explicitly declared with the BASE keyword. This
> specification does not define the value of the base IRI for SPARQL
> queries with no BASE directive.
> 
> [B]
> QNames are transformed into IRIs by appending the local name to the
> namespace name. Relative IRIs are combined with base IRIs as per
> Uniform Resource Identifier (URI): Generic Syntax [RFC3986] using only
> the basic algorithm in Section 5.2 . Neither Syntax-Based
> Normalization nor Scheme-Based Normalization (described in sections
> 6.2.2 and 6.2.3 of RFC3986) is performed. Characters additionally
> allowed in IRI references are treated in the same way that unreserved
> characters are treated in URI references, per section 6.5 of
> Internationalized Resource Identifiers (IRIs) [RFC3987].
> ]]
> 
> Paragraph A defines how prefixes and Base IRIs are defined. B shows
> how they are used. This arrangement appears to be a bit confusing. In
> addition, Martin Dürst was confused by how they can be "used" before
> being redefined (a vestige of our former grammar where prefixes
> happened in multiple places in the grammar). The only way you could
> use them, progressively constructing a namespace in multiple passes:
>   PREFIX rq23: <http://www.w3.org/2001/sw/DataAccess/Overview.>
>   PREFIX rw23: rq23:html
> is prohibited by the grammar:
>   [4] PrefixDecl ::= 'PREFIX' QNAME_NS Q_IRI_REF
> 
> We also have comments from Bjorne saying that we don't relate well to
> 3986's text on resolving URIs relative to a base URI. This text is
> intended to address all this, and world hunger to boot:
> 
> [[
> SPARQL provides a two abbreviation mechanisms for IRIs, prefixes and
> relative IRIs.
> 
> The PREFIX keyword binds a prefix to a namespace IRI [NAMESPACE]. A
> prefix binding applies to any QNames in the query with that prefix; a
> prefix may be defined only once. A QName is mapped to an IRI by
> appending the local name to the namespace IRI corresponding to the
> prefix.
> 
> Relative IRIs are combined with base IRIs as per Uniform Resource
> Identifier (URI): Generic Syntax [RFC3986] using only the basic
> algorithm in Section 5.2 .  Neither Syntax-Based Normalization nor
> Scheme-Based Normalization (described in sections 6.2.2 and 6.2.3 of
> RFC3986) is performed.  Characters additionally allowed in IRI
> references are treated in the same way that unreserved characters are
> treated in URI references, per section 6.5 of Internationalized
> Resource Identifiers (IRIs) [RFC3987].
> 
> The BASE keyword defines the Base IRI used to resolve relative IRIs
> per RFC3986 section 5.1.1, "Base URI Embedded in Content".  Section
> 5.1.2, "Base URI from the Encapsulating Entity" defines how the Base
> IRI may come from a an encapsulating document, such as a SOAP envelope
> with an xml:base directive, or a mime multipart document with a
> Content-Location header. The "Retrieval URI" identified in 5.1.3, Base
> "URI from the Retrieval URI", is the URL from which a particular SPARQL
> query was retrieved.
> ]]
> 
> 
> ISSUES:
> 
> - Do we want to alter the grammar to allow progressive declarations?
> I say "no".

+1 to "no"

The cases where it would be useful are rather few because the local part of an 
abbreviated qname can't start with "/" or "#".


Given this, I would also say the prefix IRI is resolved then the qname rules 
of concat(prefix, local part) applied.  (I can't think of case where it makes 
a difference because you can't, say split ".." across the prefix and the local 
part).  The grammar does not imply whether it's

   concat(resolve(prefix), local part)

or

   resolve(concat(prefix, local part))


I think this is fact covered by the text because "URI" in RFC 3986 means the 
whole thing and "absolute URI" as being without the fragment in
"4.3.  Absolute URI" but it might be worth making it clear.


 > The PREFIX keyword binds a prefix to a namespace IRI [NAMESPACE].

The PREFIX keyword binds a prefix to a namespace IRI [NAMESPACE] after 
relative IRI resolution has been applied.

> 
> 
> - What does
> [[
> The use of relative IRI references, including same-document
> references, in namespace declarations is deprecated.
> 
> Note:
> 
> This deprecation of relative URI references was decided on by a W3C
> XML Plenary Ballot [Relative URI deprecation]. It also declares that
> "later specifications such as DOM, XPath, etc. will define no
> interpretation for them".
> ]]
> mean in the namespaces spec [NSPACE]?


There would be an implication on SPARQL that apps shoudl not use relative IRIs 
in PREFIX.

	Andy

> 
> 
> - 3986 talks about SPARQL inside SOAP. SPARQL Protocol should as well.
> 
> 
> - 3986 doesn't mention any recursion for resolving Base URIs for
> encapsulating entities.
> 
> 
> - SPARQL uses "IRI" and 3986 uses "UIR". I tried to quote
> strategically in order to show how the terms applied to each document.
> 
> [NSPACE] http://www.w3.org/TR/xml-names11/#iri-use
Received on Monday, 26 September 2005 08:40:54 GMT

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