![]() ![]() Most data models also include a set of basic operations for manipulating data in the database. The data model is a collection of concepts or notations for describing data, data relationships, data semantics and data constraints. In the database design phases, data are represented using a certain data model. These two sub-steps are database implementation and operations/user interfaces building steps. During this step, we might have two sub-steps: one called database logical design, which defines a database in a data model of a specific DBMS, and another called database physical design, which defines the internal database storage structure, file organization or indexing techniques. This result is quite easy to understand so it is used as reference to make sure that all the user’s requirements are met. Because these concmepts do not include the implementation details, the result of the data modelling process is a (semi) formal representation of the database structure. In the second step, the data items, the relationships and the constraints are all expressed using the concepts provided by the high-level data model. The constraints on data (e.g., student number has exactly eight digits a subject has four or six units of credit only).The relationships between data items (e.g., students are supervised by lecturers lecturers teach courses).The data contained in the database (e.g., entities: students, lecturers, courses, subjects).This step is sometimes considered to be a high-level and abstract design phase, also referred to as conceptual design. Data modelling is the first step in the process of database design.
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