5 Part 5: V-Modell Reference Work Products

5.3 Products

5.3.10 System Design

5.3.10.6 Database Design

Responsible: Software Architect (when using process module Software Development)

Purpose

Data-centered software systems, e.g. information systems, need a persistent memory for data maintenance. Normally, one or more databases are used for this purpose. In this case, the system design must include an additional »Database Design. The database design supports the »Software Architect when he derives the technical »Data Model from the requirements and designs a physical database scheme.

The database design is based on the system entities to be saved in a persistent manner. The entities (relational data model) or classes (object-oriented data model) in their entirety represent the functional data model of the system. For the database design, all entities or classes of the system will be identified and summarized in the logical data model. Technical and physical data models are refinements and concretizations of the functional data model on the way to the database scheme. The Software Architect is responsible for the database design.

Is generated by

Overall System Specification (see product dependency 4.26)

Overall System Specification (see product dependency 4.25)

5.3.10.6.1 Logical Data Model

The logical »Data Model describes the entities or classes of the business model in their context. The relevant characteristics (attributes) and the interrelations of the entities or classes will be identified and described.

The logical data model can be presented as entity relationship diagram, class diagram or table. It is the basis for the design of the physical data model.

5.3.10.6.2 Physical Data Model

The physical »Data Model describes the concrete »Database Design. It is derived from the logical data model and will be used as specification for the database scheme in the database.

The physical data model allocates concrete data types to the attributes of the entities or classes. Primary and external keys will be specified, and relations will be defined. The model defines consistency conditions for changing the data. In case of relational databases, entities and attributes will be allocated to concrete tables and fields within the scheme.

Normaly, physical data models are designed by means of entity relationship diagrams or class diagrams. If suitable tools are used, the database scheme can be generated directly from the diagram.