Enterprise Architecture is a model-based approach to business-oriented IT management. To promote good IT decision making, an enterprise architecture framework needs to explicate what kind of analyses it supports. Since creating enterprise architecture models is expensive and without intrinsic value, it is desirable to only create enterprise architecture models based on metamodels that support well-defined analyses. This paper suggests a metamodel derived specifically with a set of theory-based system quality analyses in mind. The ISO 9126-based theory behind the system quality analysis is introduced in the shape of an extended influence diagram. Finally, an example illustrates that our theory-based metamodel does support system quality analysis.