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The University of Akron
Dept of Business Technology
Computer Information Systems
2440: 180
Database Concepts
Instructor: Enoch E. Damson
The Relational Model: Concepts
The Relational Model
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E. F. Codd of IBM originated the relational model
approach in the 1970s
Has been the predominant method for data storage
The central data description construct is a table
(called “relation” by Dr. Codd)
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Advantages of the Relational Model
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Logical and physical characteristics of a
database are separated
Model is simple and easy to understand
Powerful operators to enable complex
operations to be executed with simple
commands
Design of Database is simple
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Relational Databases
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Collection of relations (tables or entities)
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Records (rows or tuples) contain data about entities
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Attributes (columns or fields) contain data about
properties of the entities
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Relationships are common columns in two or more
tables
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Order of rows and columns is unimportant
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Repeating groups are not permitted
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Entries with repeating groups are unnormalized
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Relation
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Two dimensional table in which:
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Entries are single-valued
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Each column (field or attribute) has a distinct name
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All values in a column represent the same attribute
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Order of columns is immaterial
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Each row (record or tuple) is distinct
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Order of rows is immaterial
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Schema
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Database structure representation
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Description of a database (in terms of a data model)
Relational model schema for a relation specifies:
Name of the relation
 Name of each field (attribute or column)
 Type of each field
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Schema Representation
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Write the name of the table followed by a list of all
columns (and column types) within parentheses
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E.g., Students (sid: char, name: char, login: char, age: integer,
gpa: numeric)
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Underline unique key (primary key)
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Each table should appear on its own line
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Use the notation, tablename.columnname, with
duplicate column names within a database
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Using this combination qualifies column names
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View (Subschema)
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Subset of a schema
Benefits of views include:
 Making databases simpler
 Securing information
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Other Relational Model
Terminologies…
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Normalization – disallowing repeated groups in a table
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Query – an approach that helps obtain information from a database
Data Definition Languages (DDLs) - approaches to data definition
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E.g. Structured Query Language (SQL)
Data Manipulation Languages (DMLs) - approaches to data manipulation
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Normalized relation – has no repeating groups
Unnormalized relation – allows repeated groups
E.g. Query-by-Example (QBE), Relational Algebra, SQL and Relational Calculus
Structured Query Language (SQL) – the language that defines and manipulates
relational databases
Entity-Relationship Diagram (ERD) - diagram that visually represents
database structure
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Other Relational Model
Terminologies
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Integrity Constraint – rules applied to a
DBMS to perform specific functions on a
database
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There are several types of key constraints:
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Primary key
Composite key
Candidate keys
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Surrogate key (synthetic key)
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Foreign key
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Types of Key Constraints
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Primary key – the column (or collection of columns) that
uniquely identifies a given row in a table
Composite key – a primary key with two or more fields
Candidate keys – other unique keys in a table that are capable
(or candidates) of being used as the primary key
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Surrogate key (synthetic key) – system-generated primary
key usually hidden from users
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Foreign key – the field in one relation required to match the
primary key of another relation to specify relationships between
the relations and to ensure referential integrity constraints
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