DBMS
Lossless Decomposition and Dependency Preservation
A decomposition is lossless when joining the pieces reproduces the original exactly, and dependency preserving when every dependency can still be chec...
#Advanced
Advanced level material.
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DBMS
4NF, 5NF, Multivalued and Join Dependencies
Fourth normal form removes independent multivalued facts stored in one relation. Fifth normal form removes join dependencies, where a relation can be...
DBMS
BCNF and BCNF Decomposition
BCNF requires every determinant to be a super key. It is stricter than 3NF, removes the last key based redundancy, and sometimes cannot be reached wit...
DBMS
Equivalence of FD Sets and Minimal Cover
Two dependency sets are equivalent when each implies the other. A minimal cover is the smallest equivalent set, computed in three steps, and it is wha...
DBMS
Armstrong Axioms and Inference Rules
Three primary axioms - reflexivity, augmentation and transitivity - are sound and complete, meaning they derive every dependency that follows and none...
DBMS
Building Relational Algebra Expressions
How to turn an English question into an algebra expression, read an expression tree, and apply the equivalence rules an optimiser uses to make the sam...
DBMS
The Division Operator
Division answers questions containing the word every. It is the hardest operator to recognise and the easiest to verify, and it can always be rewritte...
DBMS
Outer Joins, Semi Join and Anti Join
Inner joins discard unmatched tuples. Outer joins keep them and pad with nulls. Semi join keeps only the left tuples that matched, and anti join keeps...
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
Object Oriented and Object Relational Models
The object oriented model stores objects with identity, state and behaviour. The object relational model adds those ideas to a relational core, which...
Java
Modern Java: A Version Feature Guide
What changed in each release since Java 8, which old habits it replaces, and what to reach for in new code today.
Java
Immutability and Defensive Copying in Java
An immutable object cannot change after construction, which removes whole categories of bug at the cost of a little copying.