The association and relational classes provide links between related objects. This device permits an SMS object to be linked to any number of other objects, such as a collection being linked to an advertisement as well as to multiple subcollections.
Most of the association objects contain only two properties. Both properties reference an SMS object and both properties are indexed (for rapid database searching). The association object forms a two-way link between the two SMS objects.
These classes can be queried, but there is little reason to do so. They contain no information beyond what is already present in the objects that they associate.