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Database Management System
Lecture 4
The Relational Database Model-
Introduction, Relational Database Concepts
Introduction
• In this lesson, an introduction to the relational database model is provided.
• Description of the main building blocks of a relational database and its definition.
Learning Outcomes
• Understand how a relation (table) is the main organization unit of a database.
• Understand the main building blocks of a relational database and its definition
Terminology
• Domain A set of values that define the value range for an attribute.
• Attribute The basic unit in a relation (table) definition. Each attribute has a domain associated with it.
Terminology (Cont.)
• Relation Schema (Table Schema) Defines the structure of a relation (table) which consists of a set of attributes and an association between each attribute and its domain
• Relational Database Schema A collection of relation (table) schemas
Terminology (Cont.)
• Tuple (record/row) A list of values with each value being an element in a domain or NULL. A tuple represent a record or row in a table (relation).
• Relation (Table) An instance of a relation schema which is composed of a set of tuples
Terminology (Cont.)
• Database A collection of relations (tables).
Introduction to the Relational Database Model
• As discussed in the previous lecture, the relational database model is the most widely used data model in DBMSs.
• It was developed by E. F. Codd at IBM in 1970.
Introduction to the Relational Database Model (Cont.)
• The relational database model is based on organizing data with the basic organization unit being a relation that is represented as a table.
Relational Database Concepts
Domain: • is a set of values that define the value range
for an attribute.
• A domain can be considered as a data type. Examples of domains include integer, float, string, date, etc.
Relational Database Concepts (Cont.)
• Relation Schema (Table Schema): defines the structure of a relation (table) which consists of a set of attributes and an association between each attribute and its domain (specifying the possible values of an attribute).
• Relational Database Schema: that is a collection of relation (table) schemas.
Relational Database Concepts (Cont.)
Attribute: • is the basic unit in a relation (table) definition.
• Each attribute has a domain associated with it. It can be considered as a column in relational database table.
Relational Database Concepts (Cont.)
• Tuple (Record/row): • that is a list of values with each value being an
element in a domain or NULL.
• A tuple represent a record or row in a table (relation).
Relational Database Concepts (Cont.)
Relation (Table):• is one instance of a relation schema which is
composed of a set of tuples.
Relational Database:• is a collection of relations (tables).
• Figure 5.1 illustrates the definition of Library database.
• A database schema is defined which consists of two relation (table) schemas: Books and Members.
• As shown in the books table schema in Figure 5.1, the schema defines the structure of the table specifying the attributes of the table (book_Id, title, author, publisher and publication_date).
• Each attribute is associated with a domain in the schema, e.g. attribute title has domain text which specifies that values of attribute title are of type text.
• Figure 5.2 illustrates the library database instance.
• It can be seen that the library database consists of two relations (tables): books and members.
• The books table is an instance of the books table schema shown in Figure 5.1.
• The books table consists of tuples (records/rows).
• Each tuple is composed of values for the attributes defined in the table schema.
• Each value in a table tuple is part of the domain associated with the corresponding attribute in the table schema.
• For example, value ‘A Tale of Two Cities’ in the 1st tuple of the book table is a value of attribute title with domain text as defined in the table schema (shown in Figure 5.1).
Summary
• An Introduction to the Relational Database Model
• The main relational database concepts.
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