Introduction to Database Systems - Database Systems - Lecture Slides, Slides of Database Management Systems (DBMS)

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Introduction to Database

Systems

Why Study Databases?

• Databases are useful
  • Many computing applications deal with large amounts of information
  • Database systems give a set of tools for storing, searching and managing this information - Databases in CS - Databases are a ‘core topic’ in computer science - Basic concepts and skills with database systems are part of the skill set you will be assumed to have as a CS graduate

Databases

• Web indexes
• Library catalogues
• Medical records
• Bank accounts
• Stock control
• Personnel systems
• Product catalogues
• Telephone

directories

• Train timetables
• Airline bookings
• Credit card details
• Student records
• Customer histories
• Stock market prices
• Discussion boards
• and so on…

Database Systems

• A database system

consists of

• Data (the database)
• Software
• Hardware
• Users
• We focus mainly on

the software

• Database systems

allow users to

• Store
• Update
• Retrieve
• Organise
• Protect

their data.

Database Management

Systems

• A database is a

collection of

information

• A database

management system

(DBMS) is the

software than

controls that

information

• Examples:
  • Oracle
  • DB2 (IBM)
  • MS SQL Server
  • MS Access
  • Ingres
  • PostgreSQL
  • MySQL

What the DBMS does

• Provides users with
  • Data definition language (DDL)
  • Data manipulation language (DML)
  • Data control language (DCL)
• Often these are all

the same language

• DBMS provides
  • Persistence
  • Concurrency
  • Integrity
  • Security
  • Data independence
• Data Dictionary
  • Describes the database itself

File Based Systems

• File based systems
  • Data is stored in files
  • Each file has a specific format
  • Programs that use these files depend on knowledge about that format - Problems: - No standards - Data duplication - Data dependence - No way to generate ad hoc queries - No provision for security, recovery, concurrency, etc.

Relational Systems

• Problems with early

databases

• Navigating the records requires complex programs
• There is minimal data independence
• No theoretical foundations - Then, in 1970,

E. F. Codd wrote “A

Relational Model of

Data for Large

Shared Databanks”

and introduced the

relational model

ANSI/SPARC Architecture

• ANSI - American

National Standards

Institute

• SPARC - Standards

Planning and

Requirements

Committee

• 1975 - proposed a

framework for DBs

• A three-level

architecture

• Internal level: For systems designers
• Conceptual level: For database designers and administrators
• External level: For database users

Internal Level

• Deals with physical

storage of data

• Structure of records on disk - files, pages, blocks
• Indexes and ordering of records
• Used by database system programmers - Internal Schema RECORD EMP LENGTH= HEADER: BYTE(5) OFFSET= NAME: BYTE(25) OFFSET= SALARY: FULLWORD OFFSET= DEPT: BYTE(10) OFFSET=

External Level

• Provides a view of

the database tailored

to a user

• Parts of the data may be hidden
• Data is presented in a useful form
• Used by end users and application programmers - External Schemas Payroll: String Name double Salary

**Personnel: char Name char Department

Mappings

• Mappings translate

information from one

level to the next

• External/Conceptual
• Conceptual/Internal
• These mappings

provide data

independence

• Physical data

independence

• Changes to internal level shouldn’t affect conceptual level
• Logical data

independence

• Conceptual level changes shouldn’t affect external levels