In the SINE platform, the user could specify the values of some parameters or some attributes of a parameter of the design. For example, the user would specify the value of the stem radius in the wine glass design.
In the new model of SiFAs, the user requirements can be any arbitrary set of constraints involving the design parameters. Then, a critic or a group of critics need to check for those constraints and detect a conflict when one of the constraints is not satisfied. See section 6.2 for a detailed explanation of conflict detection.
This approach has the disadvantage that one particular SiFA-based design system cannot be used to create multiple designs each of which satisfy a different set of user requirements. In order to have additional user requirements, the critics in the system need to be modified. A solution to this problem is automatic generation of critics. Since all critics checking for different user requirements are identical except for the constraint they check, it is possible to create them automatically. This is discussed further in section 10.5 as a future research direction.