Constraints say what characteristics a dimension-driven cell must have, but not necessarily how to arrive at a design with those characteristics. How to compute geometry in the light of constraints is the task of "solving."

Most constraint relationships apply to the design's essential layout or general structure. The design's details are located and shaped by its structure. For example, if a dimension-driven cell is generally symmetrical, it has constraints that relate elements to a center line in some way.

The following types of constraints can be created:

• Location — A constraint that fixes the location of a point in the design plane.
• Geometric — A constraint that controls the position or orientation of two or more elements relative to each other.
• Dimensional — A constraint that is a controlled by dimension.
• Algebraic — An equation that expresses a relationship among variables.

When a constraint is added, modified, or deleted, the model is resolved — an attempt is made to reconstruct the design so that the new or modified constraint, as well as all existing constraints, are satisfied.

• If a solution is found, the affected elements are updated and redisplayed. The solution may affect elements that are not obviously or locally related to the new constraint.
• If no solution is possible, the message "Not Solved" and graphical cues as to where the trouble is are displayed. The design's geometry is not updated, but the constraint is accepted anyway. If MicroStation reports "Not Solved" even though the new constraint is not redundant and you are sure that a solution is in fact possible, it may help to re-arrange the geometry of the model to look more like the solution you want and then re-solve.

Adding a new constraint removes ambiguity from the design. (Deleting a constraint has the opposite effect.)

A constraint can apply only to a construction. An element is converted to the equivalent construction when a constraint is applied to it.