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Data Modeling phases



Following are main phases for  the data modeling 


1.Conceptual Modeling 

A conceptual data model identifies the highest-level relationships between the different entities. Features of conceptual data model include:
  • Includes the important entities and the relationships among them.
  • No attribute is specified.
  • No primary key is specified.

2.Logical Modeling 

A logical data model describes the data in as much detail as possible, without regard to how they will be physical implemented in the database. Features of a logical data model include:
  • Includes all entities and relationships among them.
  • All attributes for each entity are specified.
  • The primary key for each entity is specified.
  • Foreign keys (keys identifying the relationship between different entities) are specified.
  • Normalization occurs at this level.
The steps for designing the logical data model are as follows:
  1. Specify primary keys for all entities.
  2. Find the relationships between different entities.
  3. Find all attributes for each entity.
  4. Resolve many-to-many relationships.
  5. Normalization.
3.Physical Modeling 

Physical data model represents how the model will be built in the database. A physical database model shows all table structures, including column name, column data type, column constraints, primary key, foreign key, and relationships between tables. Features of a physical data model include:
  • Specification all tables and columns.
  • Foreign keys are used to identify relationships between tables.
  • Denormalization may occur based on user requirements.
  • Physical considerations may cause the physical data model to be quite different from the logical data model.
  • Physical data model will be different for different RDBMS. For example, data type for a column may be different between MySQL and SQL Server.
The steps for physical data model design are as follows:
  1. Convert entities into tables.
  2. Convert relationships into foreign keys.
  3. Convert attributes into columns.
  4. Modify the physical data model based on physical constraints / requirements.