2
Chapter 2
The Relational Database Model
2
In this chapter, you will learn:
• That the relational database model takes a
logical view of data
• That the relational database model’s basic
components are entities and their attributes, and
relationships among entities
• How entities and their attributes are organized
into tables
• About relational database operators, the data
dictionary, and the system catalog
• How data redundancy is handled in the relational
database model
• Why indexing is important
Hachim Haddouti and Rob & Coronel, Ch2
2
2
Logical View of Data
• Relational Database
– Designer focuses on logical representation rather
than physical
– Use of table advantageous
• Structural and data independence
• Related records stored in independent tables
• Logical simplicity
– Allows for more effective design strategies
Hachim Haddouti and Rob & Coronel, Ch2
3
Logical View of Data (con’t.)
2
• Entities and Attributes
– Entity is a person, place, event, or thing about which
data is collected
– Attributes are characteristics of the entity
• Tables
– Holds related entities or entity set
– Also called relations
– Comprised of rows and columns
Hachim Haddouti and Rob & Coronel, Ch2
4
Table Characteristics
2
• Two-dimensional structure with rows and columns
• Rows (tuples) represent single entity
• Columns represent attributes
• Row/column intersection represents single value
• Tables must have an attribute to uniquely identify each row
Hachim Haddouti and Rob & Coronel, Ch2
5
2
Table Characteristics (con’t.)
• Column values all have same data format
• Each column has range of values called attribute
domain
• Order of the rows and columns is immaterial to the
DBMS
Hachim Haddouti and Rob & Coronel, Ch2
6
Keys
•
•
•
2
One or more attributes that determine other attributes
– Key attribute
– Composite key
Functional dependence ( knowing STU_NUM you can determine
STU_LNAME)
Entity integrity
– Uniqueness
– No ‘null’ value in key ( NULL= 0?)
• Example: AUI ID#, Invoice#, CIN#
Hachim Haddouti and Rob & Coronel, Ch2
7
2
Keys (con’t.)
• Superkey
– Uniquely identifies each entity in a table
• Candidate key
– Minimal superkey
• Primary key
– Candidate key to uniquely identify all other
attributes in a given row
• Secondary key
– Used only for data retrieval
• Foreign key (logical pointer)
– Values must match primary key in another table
Hachim Haddouti and Rob & Coronel, Ch2
8
Keys (con’t.)
Hachim Haddouti and Rob & Coronel, Ch2
2
9
2
Integrity Rules
• Entity integrity
– Ensures all entities are unique
– Each entity has unique primary key (not null)
• Referential integrity
– Foreign key must have null value or match primary key
values (every non-null FK must reference an existing
primary key)
– Makes it impossible to delete row whose primary key
has mandatory matching foreign key values in another
table
– No dangling references ( Links in HTML?)
Hachim Haddouti and Rob & Coronel, Ch2
10
2
Relational Database Operators
• Relational algebra determines
table manipulations
• Basic operators
– SELECT
– PROJECT
– JOIN
• Other operators
–
–
–
–
INTERSECT
UNION
DIFFERENCE
PRODUCT
Hachim Haddouti and Rob & Coronel, Ch2
11
2
Union
Combines all rows
•
•
Set-oriented union, duplicates will
be eliminated
(columns and domains must be
identical), same Attribute
characteristics
Hachim Haddouti and Rob & Coronel, Ch2
12
2
Intersect
Yields rows that appear in both tables
Figure 2.6
Hachim Haddouti and Rob & Coronel, Ch2
13
2
Difference
Yields rows not found in other tables
Figure 2.7
•
Set-oriented difference
columns and domains must be identical, same
Attribute characteristics
•
Hachim Haddouti and Rob & Coronel, Ch2
14
2
Product (Cartesian product)
Yields all possible pairs from two tables
Hachim Haddouti and Rob & Coronel, Ch2
15
2
Select
Yields a subset of rows based on specified criterion
Figure 2.9
Hachim Haddouti and Rob & Coronel, Ch2
16
2
Project
Yields all values for selected attributes
(vertical subset of a table)
Hachim Haddouti and Rob & Coronel, Ch2
17
2
Join
Information from two or more tables is combined by equal
AGENT_CODE
Hachim Haddouti and Rob & Coronel, Ch2
18
2
Natural Join Process
• Links tables by selecting rows with common
values in common attribute(s)
• Three-stage process
– Product creates one table
– Select yields appropriate rows
– Project yields single copy of each attribute to
eliminate duplicate columns
Hachim Haddouti and Rob & Coronel, Ch2
19
2
Other Joins
• EquiJOIN
– Links tables based on equality condition that
compares specified columns of tables
– Does not eliminate duplicate columns
– Join criteria must be explicitly defined
• Theta JOIN
– EquiJOIN that compares specified columns of
each table using operator other than equality one
• Outer JOIN
– Matched pairs are retained
– Unmatched values in other tables left null
– Two types: right and left
Hachim Haddouti and Rob & Coronel, Ch2
20
2
Data Dictionary and System Catalog
• Data dictionary
– Provides detailed account of all tables found within
database
– Metadata
– Attribute names and characteristics
• System catalog
–
–
–
–
–
Detailed data dictionary
System-created database
Stores database characteristics and contents
Tables can be queried just like any other tables
Automatically produces database documentation
Hachim Haddouti and Rob & Coronel, Ch2
21
2
Indexes
• Points to location
• Makes retrieval of data faster
Figure 2.31
Hachim Haddouti and Rob & Coronel, Ch2
22
2
Example 1
Identify and describe the components of the database table shown below using correct
terminology.
Hachim Haddouti and Rob & Coronel, Ch2
23
2
Example 1 cont.
  1 entity set: EMPLOYEE.
  5 attributes: EMP_NUM, EMP_LNAME, etc.
  10 entities: the workers Friedman, Olansky, Fontein, and
Cruazona.
  one primary key: the attribute EMP_NUM because it
identifies each row uniquely.
• two foreign keys: the attribute DEPT_CODE, which
probably references a department to which the employee is
assigned and the attribute JOB_CODE which probably
references another table in which you would find the
description of the job and perhaps additional information
pertaining to the job.
Hachim Haddouti and Rob & Coronel, Ch2
24
2
Example1 cont.
•
Cutomer_no is superkey, (Customer_no, Customer_Name) is also
superkey for the entity set CUSTOMER
•
The combination of primary keys of the participating entity sets
forms a super key of a relationship set.
– (customer-id, account-number) is the super key of depositor
 Concept of superkey is not sufficient
PS: depositor (customer-name, account-number)
Hachim Haddouti and Rob & Coronel, Ch2
25
2
Example 2: Banking
branch (branch-name, branch-city, assets)
customer (customer-name, customer-street, customer-only)
account (account-number, branch-name, balance)
loan (loan-number, branch-name, amount)
depositor (customer-name, account-number)
borrower (customer-name, loan-number)
 Stands for PROJECT,  for SELECT, &  for Union &
INTERSECTION
Hachim Haddouti and Rob & Coronel, Ch2
26
2
Example 2 Queries
• Find all loans of over DH1200
amount > 1200 (loan)
Find the loan number for each loan of an amount greater
than DH1200
loan-number (amount > 1200 (loan))
Hachim Haddouti and Rob & Coronel, Ch2
27
2
Example 2 Queries
• Find the names of all customers who have a loan,
an account, or both, from the bank
customer-name (borrower)  customer-name (depositor)
Find the names of all customers who have a loan and an
account at bank.
customer-name (borrower)  customer-name (depositor)
Hachim Haddouti and Rob & Coronel, Ch2
28
2
Example 2 Queries
• Find the names of all customers who have a loan at the
Ifrane branch of an amount greater than DH1200.
customer-name (
amount > 1200
(borrower.loan-number = loan.loan-number(borrower x loan)))
• Find the names of all customers who have a loan at the
branch IFRANE.
customer-name (branch-name=“IFRANE”
(borrower.loan-number = loan.loan-number(borrower x loan)))
Hachim Haddouti and Rob & Coronel, Ch2
29