Introduction to Databases by Levone


									COMM1E Lecture One

               Introduction to Databases

                                           Slide 1
COMM1E Lecture One

• Some common uses of databases
• Characteristics of file-based systems
• Problems of file-based systems
• the meaning of the term database
• the major components of a DBMS
• the advantages and disadvantages of a DBMS

                                               Slide 2
COMM1E Lecture One

              Common Uses of Databases

• Try to think why each of these need to use a database:
     –   Supermarkets
     –   Insurance
     –   Credit Cards/Banking
     –   Libraries
     –   Travel Agents
     –   Universities
     –   Engineering

                                                     Slide 3
COMM1E Lecture One

                     File Based Systems


• A collection of application programs that perform
  services to end users.
• Each program defines and manages its own data.

                                                      Slide 4
COMM1E Lecture One

                     File Based Processing

                     Data Entry File handling
                     & Reports Routines
                                File Definition
                                                  Sales Files
                                File handling
                     Data Entry Routines
                     & Reports
                                File Definition
                                                  Lease Files
                                                        Slide 5
COMM1E Lecture One

        Limitations of File Based Systems

•   Separation & Isolation of Data
•   Data Dependence
•   Duplication of Data
•   Incompatible file formats

• How do we resolve these problems?

                                            Slide 6
COMM1E Lecture One

                 The Database Approach

• A shared collection of logically related data
  designed to meet the information requirements
  of an organisation

                                             Slide 7
COMM1E Lecture One

                      Database Processing
                      Data Entry
                      & reports

Sales                Application
                     Programs        DBMS

                     Data Entry             Database
                     & reports
Leases               App. Programs
                                              Slide 8
COMM1E Lecture One

   Database Management System (DBMS)

• A software system that enables users to define, create
  and maintain the database and which provides
  controlled access to the database

                                                      Slide 9
COMM1E Lecture One

                     Facilities of a DBMS
• Allows users to define the database (DDL)
• Allows users to insert, update, delete & retrieve data
• Provides controlled access
    –   a security system
    –   an integrity system
    –   a concurrency control system
    –   a recovery system
    –   a user accessible catalogue

                                                      Slide 10
COMM1E Lecture One

                 Components of a DBMS

•   Hardware
•   Software
•   Data
•   Procedures
•   People

                                        Slide 11
COMM1E Lecture One

•   Minimal data redundancy
•   Consistency of data
•   Integration of data
•   Improved integrity
•   Consistent security
•   Standards
•   Increased productivity

                                  Slide 12
COMM1E Lecture One

 •   Complexity
 •   Additional Hardware Costs
 •   Size
 •   Performance
 •   Experts -Specialised Personnel
 •   Potential organisational Conflict
 •   Higher impact of failure
                                         Slide 13
COMM1E Lecture One

                     Types of DBMS

Early Types of DBMS
     – Hierarchical
     – Network
Current Generation
     – Relational
Advanced Systems
     - Object Based

                                     Slide 14
COMM1E Lecture One

        Hierarchical Model - An Example



                     ORDER ITEM              SHIPMENT

                                                        Slide 15
COMM1E Lecture One

               Network Model - Example

                                   CUSTOMER         ORDER 1

                     ORDER 6

                                                        ORDER 2

                      ORDER 5

                                ORDER 4             ORDER 3

                                                                     ORDER ITEM 3

                                     ORDER ITEM 1     ORDER ITEM 2

                                                                          Slide 16
COMM1E Lecture One

                     Relational Database
• Relational database system devised by Codd in 1970
• An attempt to devise a standard model with a sound
  mathematical basis
     – why does this differ to the previous systems?
• Most successful database model
• Most use the query language SQL
• Examples include:
     – Oracle, Microsoft Access, SQL Server, MySQL

                                                       Slide 17
COMM1E Lecture One

           Relational Database - Example

• BRANCH relation
       branchNo         street           city           postcode
       B005             22 Deer Rd       London         SW1 4EH
       B007             16 Argyll St     Aberdeen       AB2 3SU
       B003             163 Main St      Glasgow        G11 9QX
• STAFF relation
        StaffNo      Name         Position     Salary   branchNo
        SL21         John White   Manager      30000    B005
        SG37         Ann Beech    Assistant    12000    B003
        SG14         David Ford   Supervisor   18000    B003

                                                                   Slide 18
COMM1E Lecture One


What is it?
Structured Query Language
• Used in ORACLE and other DB systems
• Non-procedural - i.e. Specify what you want not how
  to get it
• SQL - (also pronounced SEQUEL)
  directly related to the development of the

                                                  Slide 19
COMM1E Lecture One

                     Example SQL Queries

• select branchNo, city
  from branch;
• select *
  from branch
  where branchNo = ‘B003’;
• select b.branchNo, name
  from branch b, staff s
  where b.branchNo = s.branchNo;
                                           Slide 20
COMM1E Lecture One

                     Object Databases

• Current generation systems have a need to handle
  complex data for complex applications such as
     –   computer aided design
     –   computer aided software engineering
     –   geographic information systems
     –   interactive web sites
• Relational systems are inadequate for these systems
     – Why do you think this is?

                                                     Slide 21
COMM1E Lecture One

                     Object Database Types

• Object-oriented
     – extend a programming language such as Java with
       persistency and a query language
• Object-relational
     – extend a current RDBMS (e.g. Oracle) with object-oriented
• We will revisit Object databases in a later lecture

                                                            Slide 22
COMM1E Lecture One

                     Further Reading

• Introduction
     – Connelly and Begg, chapter one
• Object Oriented databases
     – Connelly and Begg, chapter 24
• Next week: Database Theory
     – Relational Model
     – Set Theory
     – SQL

                                        Slide 23

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