DBMS
Denormalisation and When to Use It
Denormalisation deliberately reintroduces redundancy to make reads faster. It is a considered trade, valid only with evidence, and it always transfers...
#DBMS Design
Designing a schema from requirements.
14 notes tagged
DBMS
Complete Worked Normalisation: Unnormalised to BCNF
One realistic table taken all the way from unnormalised form through 1NF, 2NF, 3NF and BCNF, with every dependency, key and decomposition shown at eac...
DBMS
Why Normalisation Exists: Anomalies and Redundancy
Redundancy causes three anomalies: you cannot insert a fact without an unrelated one, an update must change many rows, and a delete destroys informati...
DBMS
Functional Dependencies Explained
A functional dependency says that whenever two tuples agree on X they must also agree on Y. It is a rule about every possible instance, not an observa...
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
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
Entities, Entity Sets and Entity Types
An entity is a distinguishable thing the database stores facts about, an entity type is its definition, and an entity set is the collection of entitie...