Strengthen definitions for $orderby, $top and $skip

Total or partial order?

OData-Protocol, section 11.2.6.2 speaks of "the order" in which items are returned. Must this be a total order, or only a partial order? A partial order would not allow paging with $top and $skip. But not all services may be able to produce a total order.

This should be clarified.

Further implications of partial ordering

OData-Protocol, section 11.2.6.3 seems to allow n arbitrary items to be returned:

a non-negative integer n that limits the number of items returned from a collection.

The next sentence sounds as if a number was returned:

The service returns the number of available items up to but not greater than the specified value n.

OData-Protocol, section 11.2.6.4 is clearer:

excludes the first n items of the queried collection from the result. The service returns items starting at position n+1.

Both definitions assume that "the first n items" always exist. But in general the result set is neither totally ordered (in which case "the first n" would be well-defined) nor totally unordered (in which case n arbitrary items could be returned or skipped). After an $orderby, the result set may be only partially ordered.

The definitions of $top and $skip should make clearer what freedom to choose n items the server has.