Introduction to Databases

Case Example: File based Processing

• Real Estate Agent’s office

• Property for sale or rent

• Potential Buyer/renter

• Staff/employees

Queries

• 3-bed room apts for sales?

• Flats within 3 miles of the city?

• Average price of house?

• Average rent for 2 BR flat?

• Total annual salary for staff?

Reports

• Expected monthly turnover of renters?

• This month’s turnover compare to the last month?

Files in Sales Dept

Selling and renting of properties• Property_for_rent (Pno, Street, Area, City,

Pcode, Type, Rooms, Rent, Ono)• Owner (Ono, Fname, Lname, Address,

Tel_no, Pref_Type, Max_rent)

Potential renters

Renter (Rno, Fname, Lname, Address, Tel_No, Pref_Type, Max_rent)

Files in Contract Dept• Lease(Lno, Pno, Rent, Payment, Deposit, paid,

Start, Finish, Duration)

• Property_for_rent (Pno, Street, Area, City, Pcode, Rent)

• Renter (Rno, Fname, Lname, Address, Tel_No)

• Data entry

• File maintenance

• Reports generation

Another example

Payroll Dept

Staff_salary(Staff No, First Name, Last Name, Address, Date_of_Birth, Salary, National Insurance Number, Branch Number)

Personnel Dept:

Staff(Staff No, First Name, Last Name, Address, Telephone Number, Position, Date_of_Birth, Salary, National Insurance Number, Branch Number)

File Based Processing

Sales

Contracts

Data entry and reports

Data entry and reports

File handling routines

File handling routines

File definition

File definition

Sales application programs

Contracts application programs

Limitations of File-Based Processing

• Separation and Isolation of data

• Duplication of data

• Data dependence

• Incompatibility of files

• Fixed queries/ proliferation of application programs

Database

• “A shared collection of logically related data (and a description of this data) designed to meet the information needs of an organization.”

Entity Relationship Diagram

Staff

Property_for_Rent

Branch

Owner

Viewing

Renter

Takes

Requests

Has

Owns

OverseesIsAllocated

Parts of ER diagram

• Six entities (the rectangles): Branch, Staff, Property_for_Rent, Owner, Renter and Viewing.

• Six relationships (the diamonds): IsAllocated, Has, Overseas, Owns, Requests, and Takes

DBMS• “ A software system that enables users to

define, create and maintain the database and provides controlled access to this database.”

• Data definition Language (DDL): data types, structures and constraints on the data.

• Data Manipulation Language (DML): insert, update, delete, and retrieve data

• Query Language: general enquiry facility

• Two types of DML:– Procedural: manipulates the database record by record.– Non-Procedural: operates on a set of records.

• Most common is Structured Query Language (SQL)

• Controlled Access to the database:– security system– integrity system– Concurrency controlled, shared access– recovery control system– user accessible catalog

Database Processing

Sales

Contracts

Data entry and reports

Data entry and reports

DBMS

Database

Sales application programs

Contracts application programs

Property, Owner, Renter and Lease

details + File Definitions

Components of DBMS environment

Hardware Software Procedures People

Data

BridgeMachine Human

Hardware

• Some DBMS run only on particular hardware and operating systems

• Minimum amount of main memory and disk space to run

• Client -Server architecture:– Central computer runs the backend of the

DBMS– Other computers run the frontend

Dream Home hardware configuration

Database server Eastern OfficeWestern Office

Southern Office

Northern Office

Database

Software• The DBMS software

• Application programs: C, COBOL, Fortran, Ada etc.

• Using a fourth level language such as SQL

• Fourth generation tools:– rapid development of applications– non-procedural query languages– report generators– form generators– graphic generators– application generators

• Fourth generation tools can improve productivity.

Data• The structure of the database is called the schema.• Tables: Property_for_Rent, Owner, Renter and Lease• Attributes• System Catalog contains:

– Names, types, and sizes of data items

– Integrity constraints on data

– Names of authorized users who have access to the data

– What indexes and storage structures are being used- Tree structures.

Procedures:• Log on to the DBMS

• Use particular DBMS facility or application program

• Start and stop the DBMS

• Make backup copies of the database

• Handle hardware and software failures

• Change the structure of the table, reorganize the data across multiple disks, improve performance, or archive data to secondary storage.

PEOPLE:

• DB engineers, DB designers, DB developers/ programmers

Data and database administrators

• Data Administrator (DA)– management of data (database planning, development,

maintenance of standards, policies, procedures and conceptual and logical database design).

• Database Administrators:– Physical database design and implementation, security

and integrity control, maintanence of the operational system and ensuring satisfactory performance for the applications and users.

Database designers

• Logical database designers:– Entities, attributes, relationships, constraints

Business rules

• Physical database designers:– Decides how it is to be physically realized.

Application Programmers

• Retrieving, inserting, updating and deleting

• Programs – Third Generation Language (3GL)– Fourth Generation Language (4GL)

• End Users:– Inexperienced Users– Sophisticated users

The Paradigm Shift• The structure of the database is determined using the database

design.• Paradigm shift: think of the data first and the application later.• Poorly designed database --> errors• Well designed database --> correct information• A complete methodology for database design.

– Entity- Relationship diagram– Guidelines to help identify the entities, attributes and relationships

Advantages of Databases• Control of data redundancy• Data consistency• More information from the same amount of data• Sharing the data• Improve data integrity and improve security• Enforce standards• Economies of scale• Balance the conflicting requirements• Improve data accessibility and responsiveness• Increase productivity• Improve maintenance through data interdependencies (pgm-data independence)• Increase concurrency• Improve backend recovery services

Disadvantages of Databases

• Complexity

• Size

• Cost of DBMS

• Additional hardware costs

• Cost of conversion

• Performance

• High impact of a failure