Making an inference involves using what you know to make a guess about what you don’t know or reading between the lines. Readers who make inferences use the clues in the text along with their own experiences to help them figure out what is not directly said, making the text personal and memorable.

The Addition rule is one the common inference rule, and it states that If P is true, then P∨Q will be true.

Inference Rule (IR): The Armstrong’s axioms are the basic inference rule. Armstrong’s axioms are used to conclude functional dependencies on a relational database. The inference rule is a type of assertion. Using the inference rule, we can derive additional functional dependency from the initial set.

Inference Rules

• The Armstrong’s axioms are the most basic inference rules.
• Let X, Y and Z be three sets of attributes in the same relation R.
• The Armstrong’s axioms are: Reflexivity rule: if Y ⊆ X then X → Y. Augmentation rule: if X → Y then XZ → YZ. Transitivity rule: if X → Y and Y → Z then X → Z.

Armstrong axioms are a complete set of inference rules or axioms, introduced and developed by William W. Armstrong in 1974. The inference rules are sound which is used to test logical inferences of functional dependencies.

Functional dependency in DBMS, as the name suggests is a relationship between attributes of a table dependent on each other. Introduced by E. F. Codd, it helps in preventing data redundancy and gets to know about bad designs.

A functional dependency (FD) is a relationship between two attributes, typically between the PK and other non-key attributes within a table. For any relation R, attribute Y is functionally dependent on attribute X (usually the PK), if for every valid instance of X, that value of X uniquely determines the value of Y.

For example: Suppose we have a student table with attributes: Stu_Id, Stu_Name, Stu_Age. This is known as functional dependency and can be written as Stu_Id->Stu_Name or in words we can say Stu_Name is functionally dependent on Stu_Id.

Summary. Functional Dependency is when one attribute determines another attribute in a DBMS system. Axiom, Decomposition, Dependent, Determinant, Union are key terms for functional dependency. Four types of functional dependency are 1) Multivalued 2) Trivial 3) Non-trivial 4) Transitive.

There are 4 types of dependencies in project management viz. Mandatory, Discretionary, External, & Internal.

A set of Functional Dependencies for a data model can be documented in a Functional Dependency Diagram (also known as a Determinancy Diagram). In a Functional Dependency Diagram each attribute is shown in a rectangle with an arrow indicating the direction of the dependency.

Given a relation R, a set of attributes X in R is said to functionally determine another set of attributes Y, also in R, (written X → Y) if, and only if, each X value is associated with precisely one Y value; R is then said to satisfy the functional dependency X → Y.