ThingLab ThingLab, released in 1981 by Alan Borning of Xerox PARC, is described as a "constraint-oriented simulation laboratory," and emphasizes the importance of relations between certain objects in the system. Objects are used as organizational tools in this simulation system, and it is the system's job to maintain user-specified constraints on properties of these organizational units. ThingLab also has the inheritance hierarchy characteristic of OOPLs. ThingLab makes a modification on the basis of Smalltalk; namely, it includes constraints and the means to satisfy them. (For more information on constraints, see the paper in references.) ThingLab was influenced heavily by Smalltalk and SketchPad.