Comparison of Dynamic System Modeling Methods A. Terry Bahill* and Ferenc Szidarovszky Systems and Industrial Engineering, University of Arizona, Tucson, AZ 85721-0020 COMPARISON OF DYNAMIC SYSTEM MODELING METHODS Received 24 January 2008; Revised 26 March 2008; Accepted 26 June 2008, after one or more revisions Published online 3 October 2008 in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/sys.20118 ABSTRACT This paper compares state-equation models to state-machine models. It compares continu- ous system models to discrete system models. The examples were designed to be at the same level of abstraction. This paper models these systems with the following methods: the state-space approach of Linear Systems Theory, set-theoretic notation, block diagrams, use cases, UML diagrams and SysML diagrams. This is the first paper to use all of these modeling methods on the same examples. © 2008 Wiley Periodicals Inc. Syst Eng 12: 183–200, 2009 Key words: model-based systems engineering; UML; SysML; linear systems theory 1. INTRODUCTION System design can be requirements based, function based, or model based. Model-based system engineer- ing and design has an advantage of executable models that improve efficiency and rigor. One of the earliest developments of this technique was Wymore’s [1993] book entitled Model-Based System Engineering, al- though the phrase Model-Based System Design was in the title and topics of Rosenblit’s [1985] Ph.D. disser- tation. Model-based systems engineering depends on having and using well-structured models that are appro- priate for the given problem domain. There are two types of systems: static and dynamic. In a static system, the outputs depend only on the present values of the inputs, whereas in a dynamic system the outputs depend on the present and past values of the inputs [Botta, Bahill, and Bahill, 2006]. In computer design, these two basic types of systems are called combinational and sequential. Combinational systems do not require memory devices; hence they are called memoryless. Sequential systems require mem- ory to capture the state behavior. In combinatorial sys- tems, the output depends only on the present inputs, whereas in sequential systems the output depends on the sequence of previous inputs. In mechanical engi- neering, these two types of systems are called static and dynamic. Static systems are described with algebraic equations and the outputs depend only on the present values of the inputs, whereas dynamic systems are described with differential or difference equations and the system behavior depends on the history of the inputs. This paper only considers dynamic systems. Regular Paper *Author to whom all correspondence should be addressed (e-mail: terry@sie.arizona.edu; szidar@sie.arizona.edu). Systems Engineering Vol 12, No. 3, 2009 © 2008 Wiley Periodicals, Inc. 183