1. The Relational Database Model
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
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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
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4. Logical View of Data (con’t.)
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
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5. Table Characteristics
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
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6. 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
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Keys
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#
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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
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Keys (con’t.)
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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?)
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11. Relational Database Operators
Relational algebra determines
table manipulations
Basic operators
SELECT
PROJECT
JOIN
Other operators
INTERSECT
UNION
DIFFERENCE
PRODUCT
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Union
Combines all rows
Set-oriented union, duplicates will be eliminated
(columns and domains must be identical), same Attribute characteristics
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Intersect
Yields rows that appear in both tables
Figure 2.6
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Difference
Yields rows not found in other tables
Figure 2.7
Set-oriented difference
columns and domains must be identical, same Attribute characteristics
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15. Product (Cartesian product)
Yields all possible pairs from two tables
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Select
Yields a subset of rows based on specified criterion
Figure 2.9
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Project
Yields all values for selected attributes
(vertical subset of a table)
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Join
Information from two or more tables is combined by equal AGENT_CODE
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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
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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
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21. Data Dictionary and System Catalog
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
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Indexes
Points to location
Makes retrieval of data faster
Figure 2.31
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Example 1
Identify and describe the components of the database table shown below using correct terminology.
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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.
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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)
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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
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27. Example 2 Queries amount > 1200 (loan)
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))
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28. 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)
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29. 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)))
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