MindStudy - MindStudy

Question:

Published on: 26 December, 2024

Write short notes on the following:

Armstrong’s Axioms

Outer join

Answer:

Armstrong’s Axioms:

An inference axiom is a rule that states if a relation satisfies certain Functional Dependencies (FDs) then it must satisfy certain other FDs. These rules are applied repeatedly for a give set of FDs so that all of F+ i.e. closure can be inferred. Let X, Y, Z, W be the arbitrary schema R and XY is denoted by XY.

F1. Reflexivity If Y Í X, then X →Y holds

F2. Augmentation If X → Y then XW → YZ

F3. Transitivity If (X → Y) and (Y → Z) then (X → Z)

Computing F+ using axioms directly is quite complicated. Thus, to simplify the task of computing F+ from F, additional inference rules are derived from Armstrong’s axioms. These rules are:

F4. Union If {(X → Y) (X → Z)} then X → YZ

F5. Decomposition If (X → YZ) then X → Y

F6. Pseudo-transitivity If (X → Y) and (YZ → W) then XZ → W

Outer Join:

Outer Join is based on both matched and unmatched data. Outer Joins subdivide further into,

Left Outer Join
Right Outer Join
Full Outer Join

R1: class R2: class info

ID	Address
1	DELHI
2	MUMBAI
3	CHENNAI
7	NOIDA
8	PANIPAT

ID	NAME
1	abhi
2	adam
3	alex
4	anu
5	ashish

Left Outer Join

The left outer join returns a result table with the matched data of two tables then remaining rows of the left table and null for the right table's column.

ID	NAME	ID	Address
1	abhi	1	DELHI
2	adam	2	MUMBAI
3	alex	3	CHENNAI
4	anu	null	null
5	ashish	null	null

Right Outer Join

The right outer join returns a result table with the matched data of two tables then remaining rows of the right table left table's columns.

ID	NAME	ID	Address
1	abhi	1	DELHI
2	adam	2	MUMBAI
3	alex	3	CHENNAI
null	null	7	NOIDA
null	null	8	PANIPAT

Full Outer Join

The full outer join returns a result table with the matched data of two table then remaining rows of both left table and then the right table.

ID	NAME	ID	Address
1	abhi	1	DELHI
2	adam	2	MUMBAI
3	alex	3	CHENNAI
4	anu	null	null
5	ashish	null	null
null	null	7	NOIDA
null	null	8	PANIPAT

Subjects

C Programming and Practices Software Engineering Compiler Design Design and Analysis of Algorithm Computer Graphics and Multimedia Data Structures & Algorithm

Trending

What do you mean by ‘Ternary Relationship’? Define the concept of aggregation with suitable example.

26 December, 2024

Find out the closure of attribute set (AG), i.e., (AG)+ in R. Set of FD’s are as given: R= {A,B,C,G,H,I}, F= {A → B,A → C,CG → H,B → H}. Is (AG) a super key of R?

26 December, 2024

Design a Generalization- Specialization hierarchy for a motor vehicle sales company. The company sells motor-cycles, passenger cars, vans, buses. Justify your placement of attributes at each level of the hierarchy. Explain why they should not be placed at a higher or lower level.

26 December, 2024

State the steps involved in query processing. Why is the query optimization needed?

23 January, 2022

Write the difference between procedural and non-procedural query language.

26 December, 2024