AssocDependencies represent information about which AssocActions depend on or modify which DBObjects. This is how the associativity in the drawing is represented. Dependencies are owned by actions and are attached to the objects as persistent reactors. When the dependent-on object changes, it notifies the dependency via the persistent reactor mechanism. The dependency checks whether the change is relevant, such as when the dependency is on an endpoint of a line but the color of the line changed, or the other endpoint changed, and if yes, it changes its status indicating that it needs to be evaluated, and also changes the status of the owning action indicating that it needs to be evaluated (and the action changes the status of the AssocNetwork that owns it). 

The base AssocDependency class can be used as it but there are also provided a few concrete derived dependency classes that represent particular kinds of dependencies on particular objects or subobjects, such as on subentities (faces, edges, vertices) of geometric entities, on objects that provide a numerical value, etc. For example, the dependency on a subentity of a geometric entity keeps AssocPersSubentId of the subentity and the cached subentity geometry (such as the [x,y,z] of a vertex subentity, the Curve of an edge subentity, etc.). It can then check whether the subentity really changed by obtaining the subentity geometry from the geometric entity and comparing it with the cached geometry. If they are the same, the change notification is ignored. 

A better way to add a custom dependency class is to derive a custom AssocDependencyBody class (see comments at the AssocDependencyBody class) and make objects of this class owned by the parent AssocDependency objects. The relation between AssocDependency and AssocDependencyBody classes is analogous to the relation between AssocAction and AssocActionBody classes, so please read the comments at the AssocAction class for more information. In particular, the dependency body is fully owned by its parent dependency, such as when the parent dependency is erased, it also erases the owned dependency body. 

A more memory efficient way to implement custom dependency behavior is to use objects of the AssocDependency base class and let them delegate to the owning action (see the isDelegatingToOwningAction() property). The AssocActionBody owned by the action owning the dependency then overrides methods like AssocActionBody.IsRelevantDependencyChangeOverride() to implement the custom dependency behavior.

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.AssocDependency
        Autodesk.AutoCAD.DatabaseServices.AssocGeomDependency
        Autodesk.AutoCAD.DatabaseServices.AssocValueDependency

Public Class AssocDependency
Inherits DBObject

public class AssocDependency : DBObject;