A long time ago in an IETF working group not so far away, there was a big discussion over whether an Atom feed is really just an Atom entry that contains other entries. At the time, I wrote a long email on the subject, but kept putting off sending it, so it's been languishing in my out box since last November. I can't bring myself to delete it, but it would be silly to send it to the group now. So I'll post it here instead:

EXECUTIVE SUMMARY: I don't think that an entry is a feed, nor that a feed is an entry. I think that a feed is context in which content appears. That context may in some cases be an entry, but usually it's not.

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First of all, it's not about the feeds, and it's not about the entries, it's about the content. (An alternative view appears below). We start with some content to publish. We attach metadata about the content to assist in processing it. We also attach metadata about the context in which the content was published. Here's the stuff that we want to publish:

<content>
   <context>
      <title></title>
      <link ... />
      ...
   </context>
   <title></title>
   <link ... />
   ...
   This is what it's all about.
</content>

Markup DESCRIBES the element in which it appears. Content IS the element in which it appears. Since we don't like mixed content, we arrange it a little differently:

<content>
   <context>
      <title></title>
      <link ... />
      ...
   </context>
   <title></title>
   <link ... />
   ...
   <the-content>This is what it's all about.</the-content>
</content>

When we publish multiple pieces of content sharing the same context in the same document, we rearrange to avoid duplication:

<package>
   <context>
      <title></title>
      <link ... />
      ...
   </context>
   <content>
      <title></title>
      <link ... />
      ...
      <the-content>This is what it's all about.</the-content>
   </content>
   <content>
      <title></title>
      <link ... />
      ...
      <the-content>This is what it's all about.</the-content>
   </content>
</package>

But is that an accurate description of how a feed comes into being? Or is it like this: first, we decide we're going to publish an information stream. We don't yet have any content for it, but we can describe the information stream (I'll call it <context>, because I think that is a useful description of its nature):

<context>
   <title></title>
   <link ... />
   ...
</context>

Now, within the context of that stream, we publish some content (with it's metadata):

<context>
   <title></title>
   <link ... />
   ...
   <content>
      <title></title>
      <link ... />
      ...
      <the-content>Is it all about this, or the stream?</the-content>
   </content>
</context>

Purely for organization reasons, we decide to toss the stream's metadata into a bin:

<context>
   <bin>
      <title></title>
      <link ... />
      ...
   </bin>
   <content>
      <title></title>
      <link ... />
      ...
      <the-content>Is it all about this, or the stream?</the-content>
   </content>
</context>

Which came first, the content or the context? Sometimes the first piece of content comes first and leads to the creation of the context, and then the rest of the entries appear in that context. In other cases, the context is created first, followed by all of the content. In yet other cases, the context is created, and then each piece of content arises independently, and for convenience, is published within the context. Finally, sometimes content is taken from one context and redistributed within another--information about its original context is still of interest.

A conclusion: A feed either IS the context of an entry, or is a container for entries which share a context. In the latter case, it's not too much of a stretch to think of it as actually BEING the context--it is a surrogate for the context. So, a feed is a context.

Question: Could that context be thought of as being an entry? If the feed is a comment feed talking about an entry, then it seems it could (though later you'll see that I don't think so). But what if it's not a comment feed? I think that an entry must have content--content is an entry's reason for existing, even if the content is only pointed to by the XML representation of the entry. I don't think that a feed inherently has content itself--it is the context in which things that do have content appear, but it is not the content. In a comment feed, I think the content of the entry being commented about is more like metadata describing the context than actual content. So I do not think that a feed is an entry.

Question: Could an entry being though of as being a feed? I don't think so. The feed is the context. A single-entry feed may only be the context for one piece of information, in which case, they come very close together, but I don't think that the content is its context.