Modelling Constraints as Blocks

Engineering Analysis requires the Engineer to perform a variety of functions that include the construction of performance and reliability models, trade-off analysis, alternatives analysis and trade studies. These analyses often require the use of mathematical expressions and equations that are used to constrain the elements of an analysis. SysML provides a language mechanism in the form of a ConstraintBlock that is used to model the equations graphically. This is a powerful mechanism that allows the expression to be articulated along with its parameters and their types. The modeled equations can then be reused in a number of different contexts, allowing an Engineer to define the formula for Newton's second law of motion {F=m*a} or Carnot's definition, resulting in a fundamental theorem of thermodynamics {p= W/t =(mg)h/t}. One of the powerful results of modeling these equations graphically is that they can be related to other model elements such a stakeholder's Requirements, mission goals and lower level elements such as Blocks and implementation artifacts.

Enterprise Architect allows these ConstraintBlocks to be modeled and then reused as Constraint Properties on Parametric diagrams. The Constraint definitions can be grouped into libraries, and not only used in the current initiative but reused across multiple projects and initiatives. In a later topic we will see how the constraints can be built up into a network of equations and used on Parametric diagrams to evaluate alternatives, and to conduct trade-off and alternative analysis. The tool's precision and technical excellence will ensure that equations defined in this way can be created, maintained and used with rigor.