http://schema.org/DataFeed does not currently distinguish between a feed that contains all current items, vs those that don't. The Atom format defines such a notion via a 'complete' element.

This information would be useful for interpreting whether entries missing from the feed should be treated as no longer existing (if it's a complete feed), or simply not part of this partial representation of the feed (if it's not a complete feed).

Proposal

Add a simple subtype of DataFeed called CompleteDataFeed. Definition along these lines:

CompleteDataFeed:
A CompleteDataFeed is a DataFeed whose standard representation includes content for every item currently in the feed.

This is the equivalent of Atom's element as defined by Feed Paging and Archiving (RFC 5005), https://tools.ietf.org/html/rfc5005

For example (and as defined for Atom), when using data from a feed that represents a collection of items that varies over time (e.g. "Top Twenty Records") there is no need to have newer entries mixed in alongside older, obsolete entries. By marking this feed as a CompleteDataFeed, old entries can be safely discarded when the feed is refreshed, since we can assume the feed has provided descriptions for all current items.