Chapter 5: Realizing a Metadata Framework 165 Opened Object is opened for whatever reason. Note, use played or edited events if possible. Played Object was opened for rendering but not changed. Metadata change is still possible. Edited Object was opened and changed, other than metadata change. Sent Object was transmitted from the system by whatever means. Received Object was received from outside. Synchronized Object has been synchronized with the server. Note the actor fi eld indicates with what server. 5.6.8 Relationships RELATIONSHIP LEFT TO RIGHT RIGHT TO LEFT Contains The left object contains the right The right object is a object. part of the left object. Replaces The left object replaces the right The right object is object. superseded by the left object. Is version of The left object is a version of the The right object is an right object. older version of the left object. Requires The left object cannot be viewed/ The right object is read/listened, etc., without the required by the left right object object. Uses The left object uses the right The right object is used object. This is like Requires by the left object. relationship but less demanding, i.e., the left object may be enjoyed without the right be enjoyed. References The left object references to the The right object right object, i.e., it provides provides base information that is based on information about the the right object. left object. Summarizes The left object provides a The right object condensed version of the right provides more extensive object. Can be used, e.g., for information than the thumbnails. left object. As mentioned earlier, our relationships are always two-way relation- ships: they can be read either from left-to-right or from right-to-left. Naturally, the meaning of the relationship changes according to its