[DAS2] Why use URIs for feature IDs?

[Andrew Dalke]

Gregg
> As I understand it a fragment identifier approach would mean
> URI = (URL of doc feature XML is embedded in) + "#" + value of 
> feature's
> ID attribute.

As I understand it the part after the '#' is a query language
which is document type specific and used by the client.  DAS does not
define how that query language is used, so it has no meaning in the
DAS world.

http://www.ietf.org/rfc/rfc2396.txt

4. URI References

    The term "URI-reference" is used here to denote the common usage of a
    resource identifier.  A URI reference may be absolute or relative,
    and may have additional information attached in the form of a
    fragment identifier.  However, "the URI" that results from such a
    reference includes only the absolute URI after the fragment
    identifier (if any) is removed and after any relative URI is resolved
    to its absolute form.  Although it is possible to limit the
    discussion of URI syntax and semantics to that of the absolute
    result, most usage of URI is within general URI references, and it is
    impossible to obtain the URI from such a reference without also
    parsing the fragment and resolving the relative form.
  ....
4.1. Fragment Identifier

    When a URI reference is used to perform a retrieval action on the
    identified resource, the optional fragment identifier, separated from
    the URI by a crosshatch ("#") character, consists of additional
    reference information to be interpreted by the user agent after the
    retrieval action has been successfully completed.  As such, it is not
    part of a URI, but is often used in conjunction with a URI.

       fragment      = *uric

    The semantics of a fragment identifier is a property of the data
    resulting from a retrieval action, regardless of the type of URI used
    in the reference.  Therefore, the format and interpretation of
    fragment identifiers is dependent on the media type [RFC2046] of the
    retrieval result.  The character restrictions described in Section 2

    for URI also apply to the fragment in a URI-reference.  Individual
    media types may define additional restrictions or structure within
    the fragment for specifying different types of "partial views" that
    can be identified within that media type.

    A fragment identifier is only meaningful when a URI reference is
    intended for retrieval and the result of that retrieval is a document
    for which the identified fragment is consistently defined.



					Andrew
					dalke at dalkescientific.com