What should a shop's products news feed contain?

Question

I'm thinking about integrating some sort of (Atom) news feed into a shopping system, but I'm not sure how to go about it, except that I want the URIs to be the same for each representation (HTML, Atom). Let me explain through an example:

Let's say you have some arbitrary product listing page (red shoes for women). What would make the most sense to have as a news feed for that kind of URI?

Should the feed always contain all the matching products and only update the date on each feed entry if something (like price or availability) has changed? Would I have to update the entry's unique ID, too? Or should the feed only contain actual changes to the data, like "Product X now costs Y.YY"?

This also matters because the first way, I wouldn't have to store/persist feed entries, and that sounds good to me. But in the end it matters to me more what the best use for end users would be.

Answer 1

updated (which is required) must contain the date/time of the last significant modification (e.g., price change, added/removed features, etc., but not for corrections of spelling mistakes, or some unimportant change of a description).

published (which is optional) contains the date since when the product is added to the shop.

You must not change the id when you update a product (an entry needs to have the same id "across all time and space", i.e., if you have a product which is contained in several different feeds, always use the same id for it.)

Or should the feed only contain actual changes to the data, like "Product X now costs Y.YY"?

Unusual, but possible, of course (in this case, you’d need to use a new id for each entry!). I’d expect such a feed for a single product, not for category entries resp. search results. But if you think this is useful to your visitors, why not add both feeds?

<link rel="alternate" 
      type="application/atom+xml" 
      href="red-shoes-for-women_products.xml" 
      title="All products in the 'Red shoes (women)' category" />

<link rel="alternate" 
      type="application/atom+xml" 
      href="red-shoes-for-women_changes.xml" 
      title="All changes to products in the 'Red shoes (women)' category" />

(Note that the first feed in the head element should be the more important (resp. default) one.)