MDA Distilled: Principles of Model-Driven Architecture

The Four-Layer Architecture

The three layers of Figure 4-2, which comprise objects, models, and metamodels, are universal, and the OMG has standardized a terminology to ease communication about them, as shown in Figure 4-4.

• M0 contains the data of the application (for example, the instances populating an object-oriented system at runtime, or rows in relational database tables). (This is the top row in Figure 4-2.)

• M1 contains the application: the classes of an object-oriented system, or the table definitions of a relational database. This is the level at which application modeling takes place (the type or model level). (This is the second row in Figure 4-2.)

• M2 contains the metadata that captures the modeling language: UML elements such as Class, ...