In an associative dimension, the lines, arrowheads, and text are drawn as a single object. As a result, you can update a dimension as you change the size of the object with which the dimension is associated.
The DIMASO system variable controls associative dimensioning and is on by default. If DIMASO is off, the dimension line or leader, extension lines, arrowheads, and dimension text are drawn as separate objects. You can create nonassociative dimensions if you need to alter the dimension in other ways. In general, however, associative dimensions are easier to maintain.