Structures are physical components, logical objects, attributes, fields, or arrangements of other structures within a design. Structures typically answer the question of what in a design, and are typically described using nouns and adjectives.
Behaviors are an action, force, process, or control that is exerted on or by a structure with respect to the structure's external environment. In the case that only a portion of a design (a sub-design) is under consideration, other sub-designs constitute a portion of the external environment for the behavior under consideration. Behaviors typically answer the questions of how and when in a design, and are typically described using verbs and adverbs.