1. A computer implemented method for integrating multiple engineering design systems in a computer aided design (CAD) system, comprising: (a) displaying, on a display device of the CAD system, a design generator configured, via an application programming interface (API), to accept input from a designer that results in the creation of an engineering design wherein the engineering design comprises two or more different worksheets, wherein each worksheet: (i) represents a different aspect of the engineering design; (ii) comprises one or more local design objects, wherein each local design object: (1) represents a functional aspect of a component; and (2) is independent from a physical representation of the component; (iii) comprises one or more relation objects, wherein each relation object models constraints of one or more properties of the one or more design objects; (b) organizing the one or more local design objects and one or more relation objects in an Functional Layout Document (FLD); (c) storing the FLD in a data center comprising a shared database within the CAD system, wherein the shared database is shared by the two or more worksheets; and (d) using the FLD, via user input and the display device, to design an engineering design.