1. A method to be executed on a computing device for creating and modifying a diagram structure through implicit shape relationships, the method comprising: determining, by a structure engine of a diagramming application that is being executed on a processor of the computing device, a logic structure of shapes on a diagram canvas, wherein the logic structure of the shapes are based on one or more of a first position of the shapes, interrelations of the shapes, and attributes of the shapes; determining, by the structure engine, the implicit shape relationships between the shapes and a subset of the shapes in response to receiving a first action based on the logic structure of the shapes, wherein the first action includes one or more of a mouse-based action and a command based action through selection of a command in a menu associated with the shapes; determining, by the structure engine, effects of the first action on the subset of the shapes; allocating, by a diagram structure application programming interface (API) of the diagramming application, the subset of the shapes to a group; applying, by the diagram structure API, the effects of the first action based on special behaviors associated with the first action and shape attributes through a user interface of the diagramming application to the subset of the shapes and the group; displaying, by the diagram structure API, the group on the diagram canvas through the user interface of the diagramming application; and determining, by the structure engine, the implicit shape relationships between the shapes and the subset of the shapes in response to receiving a second action associated with the logic structure of the group.