The ResourceProxy refers to another component metadata instance (e.g. for grouping metadata descriptions into collections) The ResourceProxy refers to a file that is not a metadata instance (e.g. a text document) The ResourceProxy refers to a (SRU/CQL) web service that can be used to query the resource described in this file The ResourceProxy refers to a web page that can be used to query the resource described in this file The ResourceProxy refers to a web page that contains the "original context" of the resource described in this file (e.g. repository web page displaying the metadata).