Robert Sayre wrote:
> Temporal order of what? They are all the same entry, so what is it
> you are temporally ordering?
We are discussing the temporal ordering of multiple non-identical
*instances* of a single Atom entry. It is common in the realm of software
engineering to deal with this concept of "instances." Things are often
considered to be simultaneously "different" and "the same". (I am who I am
today -- as I was when I was a child, nonetheless, I am very different today
than I was when I was a child. The instance of me today differs from the
instance of me that you might have come across many years ago.) But, perhaps
this concept is too abstract for some readers...
> Why is this a new problem that only arises when we allow multiple
> IDs in the same feed?
I have been pointing out these issues since long before the issue of
"multiple IDs" (multiple instances) recently regained attention. The issue
exists even without duplicate id support but is particularly critical once
we support multiple instances of an entry in a single feed document.
In the absence of "duplicate id" support, a reader can infer the
temporal order of entries by simply noticing the order in which the entry
instances were read from a feed document. (If duplicate ids are prohibited,
then if you have read two entry instances which share a common atom:id, they
must have been read from different instances of feeds and at different
times. Thus, you can infer in some cases that the temporal ordering of the
entry instances approximates the temporal ordering of the read operations
which retrieved the entry instances. )
However, if you permit multiple instances of an entry in a single
feed document then it is possible that you will read multiple entries whose
temporal order cannot be inferred. (Note: Order of appearance in a feed does
not imply any inter-entry order and thus cannot be used to infer or discover
the temporal ordering of entries.)
Thus, this issue *is* related to the "multiple ID" issue in that the
problem is exacerbated by permitting multiple instances of a single entry in
a single feed document. Whether or not it is relevant in other contexts is
largely irrelevant since it appears that addressing the issue in one context
will resolve it in other contexts as well.
bob wyman
