The concept of <Control Links> can be applied to a wide range of problems related to representing control over the values of fields and states of SEDRIS objects, as well as representing the behaviour of such control. This overview will begin by discussing <Control Links> in the context of the three original issues that they were originally designed to address. Readers are encouraged to evaluate <Control Links> and consider how they might be used or extended to solve their own problems.

The three original issues were:

1. Transmittals need a mechanism to allow a consuming system to dynamically control objects within a transmittal. The need for this control extends beyond extracting individual <Model> instances for use as "moving models", or objects that are moved through or within the parent transmittal; it includes the need to identify and control the state of objects that are part of the environment that have dynamic behaviour. Examples of these objects include:
   
   
   • moving objects, e.g. wind socks, rotating beacons
   
   
   
   • objects that change appearance dynamically, e.g. with changing radiance
   
   
   
   • destructible objects, e.g. bridges, buildings
   
   
   
   • the thermal energy of an automobile as it starts up
   
   
   
   • tank gun and turret



2. Transmittals shall be able to represent how the behaviour or state of one object affects other objects in the transmittal. Examples of such objects include
   
   
   • the relationship of the rotation of various gears in a gear system
   • the relationship of the tail rotor rotation to the main rotor rotation on a helicopter



3. Transmittals shall be able to represent instances of <Model> instances in which some of the attributes of the <Model> change from instance to instance. This type of <Model> is sometimes referred to as a "smart instance" or "basis set". Examples include:
   
   
   • object clusters, e.g. trees, in which the elevation of each object shall reflect the elevation of the terrain surface below the object
   
   
   
   • generic objects, e.g. houses, that may have different colours in different instances
   
   
   
   • objects (e.g. buildings, bridges) in which the vertices representing polygons that "touch" the terrain are required to conform to the terrain without distorting the remaining vertices, so that the object is "level"