6 Part 6: V-Modell Reference Activities

6.3 Activities

6.3.10 System Design

6.3.10.6 Preparing Database Design

Purpose

The specialist »Data Model in the project specification shall be derived for the »Database Design and represented in the logical data model. Finally the physical data model, which will serve as a template for the database schema, shall be prepared from the logical data model by refining and normalizing this model and by defining integrity constraints.

6.3.10.6.1 Deriving Logical Data Model

To derive the technical »Data Model, the entities of the specialist data models shall be determined. Across the whole system the entities shall be combined in one model. The attributes and their data types shall be defined, and the relationships between the entities shall be determined.

The logical data model shall be checked for consistency with the design of the architecture of the »Software Units. For each entity of the logical data model one mapping onto elements of one of the »Software Architectures shall be defined. Across the different models mapping rules between architectures and the database shall be defined uniformly.

When using object-oriented paradigms with a relational database (which is one of the most frequent combinations), this is also called object-relational mapping. In this case rules shall be provided that describe how to solve common »Database Design problems uniformly. The rules will provide for example guidelines for:

• the mapping of the entities on tables. Is generally a mapping on a scale of 1:1 used or is the structure of the tables independent of the entities?
• the handling of n:m relationships between entities. A common solution will be to use an additional table for relationships.
• the handling of keys. Which attributes will represent the keys? Are there additional technical keys required?
• the mapping of the inheritance of entities. Different options for this will be described in the literature.
• the degree of (de)normalization. To what degree will normalization be performed? To what degree will denormalization be performed (data warehouse)?
• the implementation of the map. This will be done tool-based, for example with the help of a persistence framework.

6.3.10.6.2 Designing Database Structure

For designing the actual database schema the technical »Data Model shall be expanded by technical aspects of the database; for example consistency conditions, views or technical keys have to be introduced. The aim will be to develop a schema from which the schema in the database can be directly generated.