Data Modelling is the first step in the process of database design. This step is sometimes considered as a high-level and abstract design phase (conceptual design). The aims of this phase is to:
- Describe what data is contained in the database (e.g. entities: students, lecturers, courses, subjects etc.)
- Describe the relationships between data items (e.g. Students are supervised by Lecturers; Lecturers teach Courses )
- Describe the constraints on data (e.g. Student Number has exactly 8 digits; a subject has 4 or 6 unit of credits only)
The data items, the relationships and constraints are all expressed using the concepts provided by the high-level data model. Because these concepts do not include the implementation details, the results of the data modelling process is a (semi) formal representation of the database structure. This result is quite easy to understand so it is used as reference to make sure that all the user’s requirements are met. The third step is Database Design. During this step, we might have two sub-steps called Database Logical Design which define a database in a data model of a specific DBMS and Database Physical Design which define the internal database storage structure, file organization or indexing techniques. The last two steps shown are Database Implementation and Operations/Interfaces Building. These focus on creating an instance of the schema and implementing operations and user interfaces. In the database design phases, data is represented using a certain data model. The Data Model is a collection of conceptual concepts or notations for describing data , data relationships, data semantics and data constraints. Most data models also include a set of basic operations for manipulating data in the database.