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Re: Is a URI a uri or the entity pointed to by the uri?

  • From: Eliot Kimber <ekimber@contrext.com>
  • To: "xml-dev@lists.xml.org" <xml-dev@lists.xml.org>
  • Date: Mon, 27 Nov 2017 10:33:12 -0600

Re:  Is a URI a uri or the entity pointed to by the uri?

Your question can’t be answered as asked because you didn’t specify the *context* for the answer.

In the case of the XML document, the value of the < attendee> element is the text node http://www.example.com/SallySmith (which we can generalize to the string http://www.example.com/SallySmith as there are no subelements or other nodes in this case).

Per the XSD the value is the URI “http://www.example.com/SallySmith

How any application processing this XML document interprets the string is entirely a function of the rules defined for that application, including whether or not it is expected, allowed, or required to resolve the URI to a resource. Knowing that a string is lexically a URI doesn’t tell you much other than what characters you can expect to find (or rather, that are allowed to occur in a valid instance).

Likewise, the interpretation of that resource is entirely application dependent.

Say there is a resource that the URI http://www.example.com/SallySmith. It is, fundamentally, a sequence of bytes, which, depending on its data type might be interpreted in any number of ways—it could be a text file or an image or an XML document or a data format specific to the application resolving the URI.

What those bytes *represent* is up to the applications that access it.

If we say “this sequence of bytes represents the human Sally Smith” we have to say what “to represent” means. Does it contain Ms. Smith’s DNA signature? Her government identification records? Her phone number? Her current GPS location based on tracking her mobile phone? Her biometric signatures? How is this Sally Smith record distinguished from the millions of other Sally Smiths that must exist in the world or in other fictional domains we might discuss?

Once we get past the simple lexical representation of the data in terms of easy-to-define data types the notion of “representation” becomes very fuzzy.

Context is everything and context ultimately requires some kind of out-of-band communication, such as a pre-established agreement as codified in a standard or embodied in a specific application or simply communicated agent to agent (“I’m talking about characters in the literary universe of the Sally Smith books…”).

 

Cheers,

 

E.

 

--

Eliot Kimber

http://contrext.com

 

 

 

From: "Costello, Roger L." <costello@mitre.org>
Date: Monday, November 27, 2017 at 9:37 AM
To: "xml-dev@l..." <xml-dev@l...>
Subject: Is a URI a uri or the entity pointed to by the uri?

 

Hi Folks,

1. Here is a set:

{The Amazon River, George Washington, 3}

That set uses a name for each of its member, but the set consists of the objects named, not of the names themselves. In the set, the first president of the United States, whose name happens to be ‘George Washington’, is a member of the set. But it is the man who belongs to the set, not his name. Exactly the same set could have been described in the following way

{The Amazon River, the first president of the United States, 3}

by using an alternative description for this individual.

2. A vCard file contains this photo property:

PHOTO: http://www.example.com/pub/photos/JohnQPublic.gif

Per the vCard specification, the value of the photo property is what the URI points to, not the URI itself. So, the value of the photo property is the person John Q. Public.

3. An XML document has this attendee element:

                <attendee>http://www.example.com/SallySmith</attendee>

The XML Schema declares attendee this way:

                <element name=”attendee” type=”xs:anyURI” />

What is the value of <attendee>?

Is it:

  1. A URI
  2. A person named Sally Smith
  3. Something else (what?)

/Roger



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