DBMS
Relation Schema and Relation Instance
A relation schema is the fixed definition of a relation; a relation instance is the set of tuples in it right now. A relational database schema is the...
#DBMS
Database management system concepts.
58 notes tagged
DBMS
Relations, Tuples, Attributes and Domains
The relational model has exactly four structural terms. A relation is a set of tuples, a tuple is one fact, an attribute is a named column and a domai...
DBMS
ER Design Project: E-commerce System
An e-commerce database covering customers, products, carts, orders and payments, including why an order line must copy the price it was sold at rather...
DBMS
ER Design Project: Library System
A library database that separates a title from a physical copy, models issue and return correctly, and shows why the obvious single book table quietly...
DBMS
ER Design Project: Banking System
A banking database with a generalisation hierarchy for account types, a many to many customer to account relationship, and a transaction model that ne...
DBMS
ER Design Project: Hospital Database
A hospital database designed end to end, including a weak entity for prescription lines, a ternary relationship for treatment, and the privacy decisio...
DBMS
ER Design Project: College Database
A complete college database designed from a written requirement: entities, attributes, relationships, cardinality, participation, the ER diagram and t...
DBMS
Converting an ER Diagram into Relational Tables
Seven rules turn any ER diagram into a relational schema: entities become tables, one to many puts a foreign key on the many side, many to many become...
DBMS
Extended ER: Generalisation, Specialisation and Aggregation
The extended ER model adds inheritance to ER. Specialisation splits an entity into subclasses, generalisation combines subclasses into a superclass, a...
DBMS
Drawing and Reading ER Diagrams
A complete guide to ER notation and a repeatable eight step method for turning a written requirement into a correct, readable ER diagram.
DBMS
Strong and Weak Entities
A weak entity has no key of its own and can only be identified through an owner entity. It is drawn with a double rectangle, joined by an identifying...
DBMS
Cardinality and Participation Constraints
Cardinality says how many entities on one side may relate to entities on the other; participation says whether every entity must take part. Together t...