Model-Driven Engineering - Model-Driven and Software Product Line Engineering - page 63

mechanism. The Environmental Control feature groups
the features Air Conditioning and Automatic Windows
and also has cardinality [0..1] , which implicitly means
that Room elements can have either automatic windows, air
conditioning, or none of them as lock environmental control
mechanism.
Figure 3.4. Smart-Homes' facilities feature model
3.2.1. The 4-level metamodeling framework
Sincemetamodelsarealsomodels,theyneedtobewrittenin
another language, which is described by its meta-metamodel.
This recursive definition normally ends at that level, since
meta-metamodels conform to themselves [BÉZ 05, OMG 06B].
The OMG has introduced the Meta Object Facility (MOF),
a 4-level metamodeling framework that removes ambiguities
from the term meta [OMG 06B]. MOF can be seen as a
DSML for defining metamodels; in other words, a standard for
writing metamodels. The OMG framework is based on a four-
layer metadata architecture used to describe the relationships
between data and descriptions of them. These layers are
Information , Model , Metamodel , and Metametamodel . The
Information layer comprises the data to be described. The
Model layer contains metadata that describes the data in
the information layer. The Metamodel layer is composed