B.2 Architecture

The DD architecture distinguishes two kinds of graphical information, depending on whether language users have control over it. Graphics that users have control over, such as position of nodes and line routing points, are captured for interchange between tools. Graphics that users do not have control over, such as shape and line styles defined by language standards are not interchanged because they are the same in all diagrams conforming to the language. The DD architecture has two models to enable specification of these two kinds of graphical information, Diagram Interchange (DI) and Diagram Graphics (DG).(both models share common elements from a Diagram Common (DC) model). The DI and DG models are shown in Figure B.1 by bold outlined boxes on the left and right, respectively.

The DD architecture expects language specification to define mappings between interchanged and non-interchanged graphical information, but does not restrict how it is done. This is shown in Figure B.1 by a shaded box labeled “CS Mapping Specification” in the middle section. The DD specification gives examples of mappings in QVT, but does not define or recommend any particular mapping language. The overall architecture resembles typical model-view- controllers, which separate visual rendering from underlying models, and provide a way to keep visuals and models consistent.

The first few steps of using the DD architecture are:

1.An abstract language syntax is defined separately from DD by instantiating MOF (abstract syntaxes are sometimes called “metamodels”). This is shown in Figure B.1 by a shaded box labeled “AS” at the far middle left (the “M” levels in the figure are described in the UML 2 Infrastructure (formal/2009-02-04)).

2.Language users model their applications by instantiating elements of abstract syntax, usually through tooling for the language. This is shown in Figure B.1 by the dashed arrow on the far lower left linked to a box labeled “Model.”

3.Users typically see graphical depictions of their models in tools. This is shown in Figure B.1 by a box on the lower right labeled “Graphics.”