The physical data model is the most granular level of entity-relationship diagrams, and represents the process of adding information to the database. Physical ER models show all table structures, including column name, column data type, column constraints, primary key, foreign key, and relationships between tables.
As shown below, tables are another way of representing entities. The key parts of Entity-relationship Tables are:
Fields
Fields represent the portion of a table that establish the attributes of the entity. Attributes are typically thought of as columns in the database that the ERD models.
In the image above, InterestRate and LoanAmount are both attributes of the entity that are contained as fields.
Keys
Keys are one way to categorize attributes. ER diagrams help users to model their databases by using various tables that ensure that the database is organized, efficient, and fast. Keys are used to link various tables in a database to each other in the most efficient way possible.
Primary Keys
Primary keys are an attribute or combination of attributes that uniquely identifies one and only one instance of an entity.
Foreign Keys
Foreign keys are created any time an attribute relates to another entity in a one-to-one or one-to-many relationship.
Each car can only be financed by one bank, therefore the primary key BankId from the Bank table is used as the foreign key FinancedBy in the Car table. This BankID is able to be used as the foreign key for multiple cars.
Types
Types refer to the type of data in the corresponding field in a table. Types can also refer to entity types, which describe the composition of an entity; e.g., a book's entity types are author, title, and published date.
