All query string parameters are used to identify the resource also. RFC 3986 states
"The query component contains non-hierarchical data that, along with data in the path component (Section 3.3), serves to identify a resource within the scope of the URI's scheme and naming authority (if any)."
There is absolutely no difference between path segments and query parameters from the perspective of resource identification.
A good rule of thumb here seems to be to put identity in the path and other things in the query string. For example, to search for items with property foo equal to 12 in the music collection known as bar, the url would be /music/bar?foo=12
There is absolutely no difference between path segments and query parameters from the perspective of resource identification.