Database concepts presentation version 2010 revised

Database Concepts

Created by M Nodalo, Port Moresby International School for Year 11 Information Technology (T) - ACT/BSSS, revised 2010

ObjectiveSo that students will be able – to discuss the basic database concepts and terminologies

– data, information, field, record, key field, computed fields, field length, data types, etc.

To discuss the concept of relational database and flat-file database

To discuss the concept of SQL (structured query language)

Data Vs. InformationData – raw fact or figures Example : Max Freeman 55,000 25

Information – data that have been processed to be meaningful to the user

Example: K55,000 x .25 = K13,750

Max Freeman is a salesman who earned K55,000 sales for this month and therefore, receives 25% commission which is K13,750.

Stages of Processing Data

Input processing Output

data information• Calculating

• Sorting

• Classifying

• Analysing

• Summarising

• reporting

What is a Database?An organised collection of data items that are related to

a particular topic, purpose or activityExamples: a telephone directory, an address book, student class

list

Databases can be stored Manually (in a filing

cabinet with index cards, 3-ring binders, file folders)

Electronically using a computer system (with suitable database software)

Manual databases - concernsData duplication – same data on each fileEffects of data duplication:

More space is taken up by the filesMore work is needed to retrieve the

information

Advantages of Computerised Databases over Paper filesEasier to store large volume of informationEasier to retrieve information quickly /flexiblySpeed of information processingVersatility/flexibility in organising & reorganising

informationEasier to display, print & distribute information in a

variety of waysValidation checks may be made on the data (done

by a computer program)

Disadvantages of Computerised database over paper files

Unable to access data when there’s a computer breakdown

Ease of copying computer files; passwords needed for extra protection

Extra cost & time to train people to use the database

Planning a DatabaseDefine the purpose of the databaseDetermine the type of output reportsList all the data items (determines the fields)

Database StructureTable – a collection of related recordsRecord – a collection of data about a person or thing

made up of one or more fieldsField – a single piece of data or information common

to all records

file

recordName: Venus Jackson

Age: 27

Home Address: Gere-gere Ave., Boroko, NCD

Gender: Female

Job Position: Accounts Clerk

Pay Rate/FN: 750.00

Years in Service: 5

fields

Employee file

Example of a DatabaseTelephone Directory

Telephone Directory

Name Address Phone NumberAldo,Mark East Boroko 323-2932Amani,James Hohola 325-9022Artona,Kathy Port Moresby 323-4325

records

File/table name

Field data

Field name

Two parts of a field:1. Field name – words that represent each field data

or information, e.g.name, address, phone number, etc.

2. Field data – the actual data or information item stored in a field,

e.g. Mary Jones, Boroko, 325-3423

Designing a RecordField namesType of data (text, numeric, date, boolean,

image)Field length or size – the total number of

characters allowed for a particular fieldField description

Field length/sizeShould be designed to cope with the largest

entry possible without reserving unnecessary disk space

Too long field sizes – - will take up more space on the storage media (floppy/hard disk/CDs/flash drives)

- takes longer to process

Types of DataNumeric – contains only numbersCharacter text – numbers, letters &

other symbols can be enteredDate – date is entered as 01/09/04Logical (Boolean) – allows Y/N (yes/no)

or T/F (true/false)Image/Picture

Key FieldA field that may be used to search a fileIt makes a record unique from other records

in the filee.g. student ID number, Book ID number,

employee ID, customer code

Computed fieldContain formulas similar to spreadsheet

formulaThey display values calculated from values in

other numeric fieldsExample: Net Pay may contain formula which

calculates an employee’s net pay using Gross Pay and Tax fields

Field Name Data type Field size/length

Description

Sample database: Student file

Features of Computerised DatabasesCreate fieldsAdd and alter recordsSearch for specific recordsSort recordsPrint reports

What is DBMS?DBMS – Database Management SystemA computer program that allows you to set up a

database on computer. build a database add new data, delete or edit existing data search and extract specific data based on certain criteria

(query) change/alter the structure of the data file sort and reorganise data display data on screen / print reports security of allowing certain people to access files

What is MS Access?An example of a DBMS which was

developed by Microsoft Corporation.

Database Terms in AccessFields (columns)

Records (rows)

table – refers to a file in Access

Database Queries Issues the incompatibility of database languages created difficulty for people using different

applications to access the same database

E.F. Codd (IBM) – proposed the standardized structured English Query Language or what evolved as the SQL

Structured Query Language (SQL)Not a database management systemNot a full-featured programming language like Java or

C+.It is a sublanguage tailored for the database

environmentSQL statements – embedded inside computer programs

such as COBOL, C or other programming languagesSQL statements – understood by MS Acccess, MS SQL

Server, DB2, Oracle, Sybase & other database programs

Structured Query Language (SQL)Combines database concepts of

Tables/filesRecords (rows)Fields (columns) Mathematical concept of set

See example on pages 234-235 (Chapter 7 Database Applications and Privacy Implications, Tomorrow’s Technology and You) – 7.1 The Language of Database Queries

Structured Query Language (SQL)Basic SQL statements – filters the records of a

database to be able to extract only those records that meet specific criteria

SQL statement format:SELECT (specify fields to extract)

FROM (specify source – file name)

WHERE (specify criteria or condition using appropriate comparison operators such as AND, OR, NOT, =, >, <, <>, >=, <=)

Types of Databases• Flat file database – uses only one file at a

timeExample: MS Excel – spreadsheet list

• Relational database – consists of several files in which data can be accessed simultaneouslyExample: MS Access

Relational Database

Relational database links some tables with certain data common with other tables.

Sources• Chapter 7 – Database Applications & Privacy

Implications, Tomorrow’s Technology and You (8th ed) by G. Beekman & M. Quinn