data structures and algorithm-mapping relational

8/13/2019 DATA STRUCTURES AND ALGORITHM-MAPPING RELATIONAL

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BITSPilaniHyderabad Campus

Dr.R.GururajCS&IS Dept.

Database Design & Applications

(SS ZG 518)


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BITS Pilani, Hyderabad Campus

E(E)R to Relational Mapping(Ch. 7)

Content

1. Mapping Regular Entity types

2. Mapping Weak Entity types

3. Mapping 1:1 Relationships

4. Mapping 1:N Relationships

5. Mapping N:M Relationships

6. Mapping Multivalued and Complex attributes

7. Mapping ternary relationships

8. Mapping Class Hierarchies

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1. Mapping of Regular Entity Types.

For each regular (strong) entity type E in the ER schema,create a relation R that includes all the simple attributes ofE.

Choose one of the key attributes of E as the primary keyfor R.

If the chosen key of E is composite, the set of simpleattributes that form it will together form the primary keyof R.

Mapping entity types



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3. Mapping of Binary 1:1 Relation Types

For each binary 1:1 relationship type R in the ERschema, identify the relations S and T that correspond tothe entity types participating in R.

There are three possible approaches:1. Foreign Key approach:Choose one of the relations-say S-and include a

foreign key in S that refers to the primary key of T. It is better to choosean entity type with total participation in R in the role of S.

2. Merged relation option:An alternate mapping of a 1:1 relationshiptype is possible by merging the two entity types and the relationshipinto a single relation. This may be appropriate when bothparticipations are total.

3. Cross-referenceor relationship relation option:The third alternativeis to set up a third relation R for the purpose of cross-referencing theprimary keys of the two relations S and T representing the entity types.

Mapping Relationship types



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5. Mapping of Binary M:N Relationship Types.

For each regular binary M:N relationship type R, create a newrelationS to represent R.

Include as foreign key attributes in S the primary keys of therelations that represent the participating entity types; theircombination will form the primary keyof S.

Also include any simple attributes of the M:N relationshiptype (or simple components of composite attributes) asattributes of S.




6. Mapping of Multivalued attributes.

For each multivalued attribute A, create a new relation R.

This relation R will include an attribute corresponding to A,plus the primary key attribute K-as a foreign key in R-of therelation that represents the entity type of relationship typethat has A as an attribute.

The primary key of R is the combination of A and K. If themultivalued attribute is composite, we include its simplecomponents.

Mapping Multivaluedattributes




7. Mapping of N-ary Relationship Types.

For each n-ary relationship type R, where n>2, create a newrelationship S to represent R.

Include as foreign key attributes in S the primary keys of therelations that represent the participating entity types.

Also include any simple attributes of the n-ary relationship type(or simple components of composite attributes) as attributes ofS.

Example:The relationship type SUPPY in the ER on the next

slide. This can be mapped to the relation SUPPLY shown in the relational

schema, whose primary key is the combination of the three foreignkeys {SNAME, PARTNO, PROJNAME}

Mapping n-ary relationships




EMPLOYEE

SUPERVISION

Bdate

Ssn

Name

FName

Mint LName

Sex

Address

Salary

Works_for

DEPARTMENT

Name

Number

Location

MANAGES

Start Date

Number ofEmployee

WORKS_ON

CONTROLS

PROJECTDEPENDENTS_OF

Name

Number

Location

Hours

DEPENDENT

Name Sex BdateRelationship

Dependent

(1, 1)

(1, N)

Project

Controlled

project(1, 1)

(0, N)Controlling

department

(4, N)

department

(1, 1)

(0, N)

(0, 1)

Employee

(1, 1)

(0, 1)

Manager

Employee

SupervisorSupervisor

(0, N)

ER-Diagram for CompanyDatabase




ER-Relational mapping forCompany Database




Mapping ternary relationship




8. Options for Mapping Specialization or Generalization.

Option 8A: Multiple relations-Superclass andsubclasses

Option 8B: Multiple relations-Subclass relations only

Option 8C: Single relation with one type attribute

Option 8D: Single relation with multiple typeattributes

Mapping Class hierarchies




Option 8A: Multiple

relations-Superclass

and subclasses




Option 8B: Multiple

relations-Subclass

relations only




Option 8C: Single

relation with

one type attribute

Ssn Fname Minit Lname Birthdatae Address jobtype Typing speed Tgrade EngType

EMPLOYEE



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Exercise problem



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Summary

We have learnt the rules and guidelines for

mapping ER to Relational model.

Rules for mapping Entity typesRules for mapping Relationships

Rules for mapping Class hierarchies

data structures and algorithm-mapping relational

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