Dr. Il-Yeol Song "Developing Sequence Diagrams in UML"
(College of Information Science and Technology, Drexel University):
"...The UML (Unified Modeling Language) claims to be a language rather than a method. The UML provides a set of notations and concepts that are necessary for developing object-oriented software or systems. The UML includes nine inter-related diagrams which are used to model different aspects of the system being modeled. Among the UML diagrams, one of the most difficult and time-consuming diagrams to develop is the object interaction diagram (OID), which is rendered as either a sequence diagram or a collaboration diagram. OIDs model dynamic behavior by showing how system components interact to complete core tasks defined in use case design. While many novice designers put emphasis upon static models, they often fail to emphasize the use of dynamic models, which are very important for properly allocating responsibility among objects. ..."