RELATIONAL DATABASE MANAGEMENT SYSTEM

Department of Computer Science

St Thomas College Thrissur

• Session 1:• Introduction To DBMS

• Keys

• Functional Dependency

• Candidate Key

• Decomposition

• Normalization• Check The Normal Form

• Convert To Normal Form

• Session 2:• Transaction Processing

• Serializability

• SQL Commands

SESSION 1

DBMS• Collection of programs that enable users to create and maintain

database

• Characteristics (Self describing, sharing of data, insulation of data & program multiple usage and users)

• Advantages (redundancy control, restricted unauthorized users, back up and recovery, multiple users interface , complex relationship representation, integrity control)

• Deductive database capability of defining rules for interfacing new information

• 3 tier architecture (external, conceptual and internal )

• Data independence (logical change conceptual and physical change internal scheme)

• DBMS language DDL and DML

• Design techniques ( top down approach (ER model ) and bottom up (normalization))

• Entity objects of real world

• Simple composite single valued multi valued stored derived null complex attributes

• Keys

• Composite key

• Super key

• Candidate key

• Prime key attribute

• Primary key

• Foreign key

• Constraints

• cardinality ratio (max no of relationship instances in a binary relation

• participation constraint existence of an entity depends on another

• Total

• Partial

• Specialization and generalization

Relational schema

• Table of records

• Cardinality (tuples)

• Degree (attributes)

• Granularity (size of data item)

• Relational constraints

• Domain constraint

• Key constraint

• entity integrity

• Referential

• Semantic integrity

• Select s s salary > 2000

• Project operation (specifies a column from the relation) p name, salary( employee)

• Join operation

• Theta join

• Natural join

• inner join

• Outer join

KEYS

• uniquely identify tuple

• primary key

• Candidate key : unique & irreducibility

• Super key : uniqueness

• Foreign key

FUNCTIONAL DEPENDENCY

X Y Z

1 1 2

2 1 1

3 1 2

4 1 3

1 2 3

1 1 2

X YXYZXZY

XY iff YC XXY XZYZXY, YZ then XZIf XY, XZ then XYZIf YX, ZX union is not possibleIf XYZ then XY and XZSuppose a scheme R(A,B,C) F={AB,BC)then A+ (closure) =A.B.CB+ = BCC+ = C

CANDIDATE KEY

• Find A+

• If all attribute come in A+ then a is candidate key

• Superkeys identify the attributes but is reducible.

• Steps:

1. Find the attributes that are neither on the left and right side

2. Find attributes that are only on the right side

3. Find attributes that are only on the left side

4. Combine the attributes on step 1 and 3

5. Test if the closures of attributes on step 4 are all the attributes if the

closure does not include all the attributes, we should find the relation

exterior.

6. Find the relation exteriors, that is the attributes not included in step 4 and

step 2. 7. Now test the closures of attributes on step 4 + one attribute in

step 6 one at a time.. This will yield candidate keys.

PRIME ATTRIBUTES AND NON PRIME ATTRIBUTES

• Attribute is an attribute of candidate key prime key else non prime attribute

F CLOSURE

• Maximum number of dependencies

• Compute all possible closure combinations.

• 2 to the power (Number of elements) gives the number of dependencies of that group

• Summation of dependencies of each closure gives required result

• Note: for all relations f is considred

MEMBERSHIP

• To check if a dependency defined in a relation write closure of the lhs of the dependency. If the rhs is present in the closure then it’s a member.

DECOMPOSITION

• Splitting of tables.

• Should satisfy

• lossless join ( decompose table when we natural join them we find no spurious tuples its lossless join)

• Dependency preservation( the decomposed tables should satisfy all functional dependencies of parent)

LOSELY AND LOOSELESS DECOMPOSITION

• One row for each relation in the decomposition

• One column for each attribute of the relation

• For each row, we place the value a with the column subscript in any column whose heading represents an attribute in that relation, and the value b with the usual row and column subscript in the column for any attribute not in that relation.

• for each FD X → Y in F

• for all rows in S that have the same symbols in the columns corresponding to the attributes of X, make the symbols for the columns that represent attributes of Y equal by the following rule:

• if any row has an a value, a(j), then set the value of that column in all the other rows equal to a(j)

• if no row has an a value, then pick any one of the b values, say b(i,j), and set all the other rows equal to b(i,j)

•  4. if, after all possible changes have been made to S, a row is made up entirely of a symbols, a(1), a(2), ... , a(n), then the join is lossless. If there is no such row, the join is lossy.

DEPENDENCY PRESERVING

• Closure of FD

• Write decomposition separately

• Write all the possible fd from the closure

• Project all fd to the other

• If all fd are in the decomposition then dependency is preserved

NORMALISATION

• Property of the relation that indicates the degree of redundancy normal form

• Procedure applied on a relation to reduce redundancy normalization

• INF values are atomic

• 2NF INF + no partial dependency( set of non prime key attributes depends on the part of primary key)

• 3NF 2NF + no transitive dependency

• BCNF every determinant is a candidate or superkey

• 4NF BCNF+ No multivalued dependency

• Find the normal form:• Find candidate key

• check the FD • Skip all FD with have a candidate key on LHS.

• Of the remaining check for transitive dependency no means 3NF

• If for no candidate key there exists a relation such that a part of it determines a non prime key attribute it is in 2NF.

• If explicitly specified to be in atomic values, it is in 1NF

• Not normalized.

Notes:

• Only 1 attribute in candidate key no partial dependency

• No non-prime key attribute no transitive dependency +partial dependency + is in atomic value

• Situation where transitive dependency may exsits:

• Subsetnonprime

• Nonprime nonprime

• subset+nonprimenonprime

MINIMAL COVER

END SESSION 1

SESSION 2

TRANSACTION MANAGEMENT

SERIALIZABILITY

RELATIONAL ALGEBRA

SQL COMMANDS