Many paradigms for system analysis and design have been proposed over the years. Early approaches have advocated the functional approach. Common methodologies that support this approach are SSA and SSD (DeMarco, 1978; Yourdon & Constantine, 1979). SSA is based on the use of data flow diagrams (DFDs), which define the functions of the system, the data stores within the system, the external entities, and the data flows among these components. Early SSA and similar methodologies emphasized the functional aspects of system analysis, neglecting somehow the structural aspects, namely the data model. This was remedied by enhancing those methodologies with a conceptual data model, usually the entity-relationship (ER) model (Chen, 1976), that is used to create a diagram of the data model, which is later mapped to a relational database schema.