For each mesh part, a complete constraint set consists of several curves and points, depending on its connection circumstances with other objects. Most of the constraint geometries do not exist in the original model (for example, the intersection between two plates) and must be created.  
In the illustration below, the selfsufficient Proxy_CATPart manages all the missing geometries for constraining and mesh purposes.  
Due to a methodically organized geometrical set, all the required inputs for mesh generation are computed and aggregated under the Proxy_FEM_Geometry.  
2D Mesh Part (Plate) 

Each plate can be constrained by
curves and points. The curve/point constraints can involve the
following: Curve Constraints
Point Constraints  The intersection between a given plate and traces of the beams. 

In the table below, a pattern of plate constraints is illustrated.  
1D Mesh Part (Beam or Pillar) 

Each beam or pillar is constrained by points as a result of intersecting with other traces and/or with other plates.  