This is an empty assembly, no geometry and no constraints (it is how one would start when doing a top down design)
This is an assembly with some geometry (just dumb imported solids from step) inside the parts, still no constraints
This is similar to the one above, but this time it is with fully parametric build geometry, still nowhere no constraints (ppemawm hopefully you are ok I copied a bit from your great work )
All of the above examples are what an assembly is and there are no constraints or what so ever in this (ok maybe inside the sketches ). Of course constraints or other things like kinematics can then be added on top of such assemblies.
Few days ago there was a link to the solidworks online help, here are the first two sentences from the assemblies section http://help.solidworks.com/2016/english ... _topic.htm
Constraints (or mates in solidworks) are explained later...You can build complex assemblies consisting of many components, which can be parts or other assemblies, called subassemblies. For most operations, the behavior of components is the same for both types.
What I want to say is that constraints don't make the assemblies. It is like if I would ask someone to build foundations for a house, instead they would build the walls and then try to convince me that walls are foundations, they are not.Mates create geometric relationships between assembly components...
And part is a container, not a geometry (ex. a solid box by itself is not a part, it is something you put inside a part container).
As I have suggested before, we should IMO first get an proper assembly container in to FreeCAD, then fix the existing part and body and then split asm3 in two workbenches, one that would work on top of assembly and part containers and one that would work directly on geometry inside the part containers (since this is sort of how it is mostly working now). In my view asm3 is currently much more like another implementation of the part container then what an assembly workbench should be.