Parametrics
The SysML Parametric Diagram (PD) is used to represent the usage of constraint blocks as constraint properties. Syntactically the PD is actually is similar to IBD. In a PD, constraint properties are connected to each other through the parameters defined by their constraint block. In turn they connect to other properties in the context of their owning block. These other properties must be directly bound to parameters of the constraint properties because they can only play a “feeding role” to the constraints parameters in a PD.
An example of a PD is shown in Figure
both the sensor and windshield parts compute an operational range that is compared by the property named compare. These values are also fed to the
part representing the configuration file (bottom of the figure). If the sensor and the windshield are compatible, the flag IsCalibrated (exposed as a port) is set to true. The verification of the calibration requirement is hence reduced to testing the value of this port. The system is therefore resilient to changes in windshield and sensor characteristics.
The usage of the constraint blocks WindshieldIREffectiveRange and SensorEffectiveRange can be seen in the diagrams of Figure
An attractive aspect of constraint blocks is that they provide a reusable mechanism to define types of constraints. Hence the same constraint can be used several times in the model. It is important to note that a constraint does not specify which variable is an input or an output. Values are assigned by the
context and a numerical solver will provide results for the variables of the system.7
7See the work by Peak et al. on constraints for more details: Peak RS, Friedenthal S, Moore A, Burkhart R, Waterbury SC, Bajaj M, Kim I, Experiences Using SysML Parametrics to Represent Constrained Objectbased Analysis Templates. 2005. 7th
