AssocDimDependencyBodyBase ties together the following objects that define a dimensional constraint: 

AssocVariable Keeps dimensional constraint name and expression. Assoc2dConstraintGroup Keeps AcExplicitConstraint. Entity (such as Dimension) Graphical representation of the dimensional constraint. 

AssocDimDependencyBodyBase class represents a dependency of an ExplicitConstraint owned by an Assoc2dConstraintGroup, on an Entity that is the graphical representation of the dimensional constraint. AssocDimDependencyBodyBase is an abstract base class, there are concrete derived classes (such as AssocDimDependencyBody) that deal with concrete entity types (such as Dimension) that are used as graphical representations of dimensional constraints. 

The AssocDimDependencyBodyBase does all the work of managing the graphical entity, receiving notifications about entity text changes, updating the entity text and entity positioning, keeping the entity text in sync with the AssocVariable, and keeping it in sync with the corresponding ExplicitConstraint in Assoc2dConstraintGroup. 

There always is a corresponding AssocVariable that keeps the name, expression and value of the dimensional constraint and is also referenced by the ExplicitConstraint via AssocValueDependency. The AssocDimDependencyBodyBase obtains the corresponding AssocVariable by going up to the Assoc2dConstraintGroup that owns the AssocDimDependencyBody, finds the ExplicitConstraint that references this dependency, obtains the AssocValueDependency and obtains the object it depends on, which is the corresponding AssocVariable.

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.AssocDependencyBody
        Autodesk.AutoCAD.DatabaseServices.AssocDimDependencyBodyBase
            Autodesk.AutoCAD.DatabaseServices.AssocDimDependencyBody

Public abstract Class AssocDimDependencyBodyBase
Inherits AssocDependencyBody

public abstract class AssocDimDependencyBodyBase : AssocDependencyBody;