Uniqueness requirement in XDI Addressing Strawman

["Drummond Reed" <drummond.reed@cordance.net>]

XDI TC Members and Observers:

I've uploaded an XDI addressing strawman (see below). This proposes the
rules for addressing elements in XDI documents using XRIs.

I had an action item to outline the issue raised on the call last week RE
the proposed rule that all XRIs for Resources or Links under a parent
Resource or Link must be unique. As Dave McAlpin pointed out on the call,
this is different that XPath, which has no requirement that XPath values be
unique within an XML document. Instead, an XPath query that matches multiple
elements within an XPath document produces a result set that includes all
those elements.

I fully understand the need for this feature in XPath, however XPath was
designed as an addressing syntax for all XML documents, and XDI documents
are a highly constrained subset of those documents. In this highly
constrained subset, I believe the fundamental requirement when it comes to
addressing is the same as the fundamental requirement of Web addressing,
which is that every Web resource is addressable using at least one unique
URI.

If this same concept is applied to XDI, then it follows that every XDI
Resource (or Link) must be uniquely addressable using at least one unique
XRI. (Note that allowing more than one unique URI/XRI is allowed in both Web
and Dataweb architecture.) This is the justification for the proposed XDI
addressing rules.

Another way to look at it is that XDI is really a distributed database (or
directory, depending on your POV) represented in XML. A fundamental
principle of database or directory design is that indexing values must be
unique in every namespace. XRIs are the indexing values of the XDI
distributed database/directory (and Resources or Links are the namespaces),
so this is the source of the uniqueness requirement.

Please do post any other points of view, as XDI addressing is intimately
linked to the XDI metaschema design - neither is really complete until both
are done and they are fully integrated.

=Drummond 

-----Original Message-----
From: drummond.reed@cordance.net [mailto:drummond.reed@cordance.net] 
Sent: Tuesday, May 18, 2004 3:31 PM
To: xdi@lists.oasis-open.org
Subject: [xdi] Groups - xdi-addressing-strawman-v1.doc uploaded

The document xdi-addressing-strawman-v1.doc has been submitted by Drummond
Reed (drummond.reed@cordance.net) to the OASIS XRI Data Interchange (XDI) TC
document repository.

Document Description:
Preliminary XDI Addressing strawman explaining the proposed rules for
addressing nodes in XDI documents using XRIs.

Download Document:  
http://www.oasis-open.org/apps/org/workgroup/xdi/download.php/6816/xdi-addre
ssing-strawman-v1.doc

View Document Details:
http://www.oasis-open.org/apps/org/workgroup/xdi/document.php?document_id=68
16


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