1. A non-transitory computer-readable medium storing computer-executable instructions, the medium holding: one or more instructions for receiving a graphical model, wherein the graphical model comprises a plurality of entities and connectivity information between the entities, wherein the entities comprise properties, behavioral descriptions, and optionally behavioral constraints; one or more instructions for receiving a symbolic expression for the graphical model, wherein the symbolic expression represents a property of a first entity in the graphical model; one or more instructions for identifying a second entity comprising the property represented by the symbolic expression, wherein identifying is based on at least one of the connectivity information, a behavioral description, or a behavioral constraint; one or more instructions for propagating the symbolic expression to the second entity; one or more instructions for expressing the second entity in terms of the propagated symbolic expression; one or more instructions for identifying an under-specified constraint between the symbolic expression and a second symbolic expression, when the symbolic expression and the second symbolic expression do not inherently conflict but the second entity of the graphical model is unable to be expressed in terms of the symbolic expression or the second symbolic expression; and one or more instructions for generating a constraint between the symbolic expression and the second symbolic expression when the under-specified constraint exists, wherein the generated constraint is consistent with the graphical model.