Re: [Psidev-ms-dev] Relative URIs and RFC-2396

[Matthew C. <mat...@va...>]

You are right Randy, we were forgetting about relative URIs which can 
simply refer to a resource's name with no path at all ("1" is certainly 
a valid resource name). However, I think anyURI is still a bad idea for 
any attribute which is not intended to be able to refer to something in 
a remote location (e.g. not in the current file). The "id" attribute in 
the XML namespace has type "xs:ID" which has semantics more along the 
lines of what I think you want. If I understand the use case correctly, 
it is desirable to be able to link to certain mzML elements from 
external documents with a URI, like:
file://data_source.mzML#s555
This is an example absolute URI reference to a spectrum in a file at 
"data_source.mzML" where the spectrum's id attribute is "s555". It 
wouldn't make sense for the id itself to be a URI, although the 
reference to it can (and should) be.

So:
1) for id attributes which can be referred to externally or internally, 
use the type "xs:ID"
2) for references to external or internal resources by their id 
attribute, use the type "xs:anyURI"

This would have the problem of the Xerxes C parser not validating 
relative URIs correctly, but that seems to be wrong on their part. :/ 
Anyway, users of Xerxes C can turn off the validation feature to work 
around it.

Also, Ref attributes in mzML could use anyURI for consistency reasons 
even though we don't currently know of a use case where such references 
would be made to an external file.

-Matt


Randy Julian wrote:
>
> Per our conversation today, the relevant specification is RFC-2396:
>
> http://www.ietf.org/rfc/rfc2396.txt
>
> Section 5 talks about relative URIs. They do not need to include the 
> protocol and their syntax would include all integers:
>
> The syntax for relative URI takes advantage of the <hier_part> syntax
>    of <absoluteURI> (Section 3) in order to express a reference that is
>    relative to the namespace of another hierarchical URI.
>  
>       relativeURI   = ( net_path | abs_path | rel_path ) [ "?" query ]
>  
>    A relative reference beginning with two slash characters is termed a
>    network-path reference, as defined by <net_path> in Section 3.  Such
>    references are rarely used.
>  
>    A relative reference beginning with a single slash character is
>    termed an absolute-path reference, as defined by <abs_path> in
>    Section 3.
>  
>    A relative reference that does not begin with a scheme name or a
>    slash character is termed a relative-path reference.
>  
>       rel_path      = rel_segment [ abs_path ]
>  
>       rel_segment   = 1*( unreserved | escaped | ";" | "@" | "&" | "=" | "+" | "$" | "," )
>
> That means that you don’t need the net_path part or the abs_path part 
> but can use the rel_path part alone. The rel_path part can have only 
> the rel_segment part which is required to have one or more unreserved 
> characters (includes all the integers) and/or any of the above special 
> characters or escaped characters.
>
> The point of using it in mzML for IDs is that you can be assured of it 
> being a valid relative path when extended by all the other components 
> needed to navigate to a referenced document (protocol, absolute path, 
> etc.).
>
> We can achieve this by convention by saying in the mzML spec doc (and 
> possibly putting the required pattern in the schema), that the string 
> for ID must conform to RFC-2396.
>
> Randy
>
> Randall K Julian, Jr. Ph.D.
> President
> Indigo BioSystems, Inc.
> (317) 536-2736 x101
> (317) 306-5447 mobile
>
> www.indigobio.com <http://www.indigobio.com/>
>
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