eTag, modified and accessed attributes in Link Extensions Draft

[Bob Wyman <bob@xxxxxxxx>]

The draft, as currently written, seems to be a bit ambiguous about the source eTags and the meaning of "modified".

My assumption is that an eTag, when used as a link attribute, should not be something generated by the link element creator but should be a mere passing on of an eTag generated by the server that hosts the resource that is linked to. Thus, eTag should be seen as something which, like "hash", simply records and passes on information related to the state of the resource at some specific point in time when it was previously accessed. In this case, you could never have a eTag attribute on a link if the linked-to server did not support eTags. If this assumption is correct, I think it might clarify things if it were stated in the draft.

It seems that "modified" might be slightly different. In some cases, it seems reasonable that modified would be the modified or updated date reported on accessing a web resource. On the other hand, it seems like it would also be reasonable, in cases where the server does not report modified dates yet the author of the link has knowledge of the modification history, that the link author might include a modified date even though it is NOT reported by the server. However, this means that the link author is not simply recording and passing on data offered by the server. This means that the meaning of "modified" would be somewhat ambiguous. Am I reading this right?

I continue to see evidence that formal systems for "Internet citation" or bibliography typically require that a "last accessed" date be included in citations. Thus, I'd like to suggest a new section (as discussed in earlier messages):

X.  The 'accessed' attribute

   The 'accessed' Attribute specifies a date and time when the
   resource identified by the atom:link or atom:content element was 
   accessed. The 'accessed' attribute SHOULD record the most recent date
   and time at which the resource was accessed. The value MUST conform
   to the "date-time" production defined by [RFC3339].  An uppercase 
   "T" character MUST be used to separate date and time, and an
   uppercase "Z" character MUST be present in the absence of a numeric
   time zone offset.  The 'accessed' attribute MAY appear as a child
   of the atom:link and atom:content elements.

     accessed = attribute accessed { xsd:dateTime }

   An example accessed attribute for an enclosed MP3 file:

     <atom:link rel="enclosure"
       href="" href="http://example.org/media/myfile.mp3">http://example.org/media/myfile.mp3"
       accessed="2010-12-12T12:12:12Z" />

bob wyman