The simplest relationship is a collection, in which objects in a set share a common aspect. The results of a query or a multiple selection of objects are examples of a collection. The significance of a collection is that it enables operations to be applied to a set of objects.
A constraint is a stronger relationship between a set of objects in that changing an object in the set affects some other object in the set. The way a text box streams text, the way a drawing application layers its objects, and even the way a word-processing application organizes a document into pages are all examples of constraints.
When a relationship between objects becomes so significant that the aggregation can be identified as an object itself with its own set of properties and operations, the relationship is called a composite. A range of cells, a paragraph, and a grouped set of drawing objects are examples of composites.
Another common kind of relationship found in the interface is containment. A container is an object that is the place where other objects exist, such as text in a document or documents in a folder. A container often influences the behavior of its content. It may add or suppress certain properties or operations of an object placed in it. In addition, a container controls access to its content as well as what kind of object it will accept as its content. This may affect the results when transferring objects from one container to another.
All these aspects contribute to an object's type, a descriptive way of distinguishing or classifying objects. Objects of a common type have similar traits and behaviors.