TN TRB Computer Science Syllabus - Business Computing #3 Data Models - Entity Relationship Model

Tamil Nadu TRB Computer Instructor GRADE1 Exam Syllabus Business Computing - Data Models - Entity Relationship Model - ERD --------------- Data Models * Structure of the Data base * to describe the data, data relationship, data type ... Data Base * Collection of information that is organized * So, data can be easily stored, managed, updated and retrieved Different types of Data Models * Relational Models * Entity Relational Models (ERD) * Object based Data Models * Semi-Structured Data Models Eg: Shopping cart orders Data (Customers, Order, and Product) Entity Relational Model Visual way to understand the database structure is called Entity Relational Model (ERD). Components of ERD * Entities # An object (Person, place, or thing) to be tracked in DB (Table) # EG: Customer, Order, Product # An entity is a row in DB table * Attributes # Property of an Entities # Column in DB table * Relationship # How the Entities interact with each other # Interaction between Entities is described by a line * Cardinality # Notations in Entities Relationship # Crow foot notations to describe the relationship * One relationship * Many relationship * One and only One relationship * Zero or One relationship * One or Many relationship * Zero or Many relationship Define Mininum and Maximum number of intractions between Entities Eg: Customer & Order Entities Customer * Minimum Order – 0 * Maximum order – Infinate # Zero or Many Order * Minimum customer per order – 1 * Maximum customer per order – 1 # One and only One Order & Product Entites Order * Mininum product per order – 1 * Maximum product per order – Infinate # One or More Product * Minimum order for a product – 0 * Maximum order for a product – Infinate # Zero or More Keys * Primary Key * Foreign Key NOTE: * Each entity repesents table in DB * A Primary key is is an attribute (or field) that uniquly identifies every record in a certain table. * One Primary key per Entity Primary Key * Should be Unique * Never changing * Never null Foreign Key * Same as Primary key located in foreign place * Can be repeated in the table * There can be multiple Foreign keys in one Entity Composit Primary key * Two or more attributes to identify the unique record NOTE: ER Diagram can have Data type of the attribute, that describes more technically.