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Database Concepts
Created by M Nodalo, Port Moresby International School for Year 11 Information Technology (T) - ACT/BSSS, revised 2010
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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)
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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.
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Stages of Processing Data
Input processing Output
data information• Calculating
• Sorting
• Classifying
• Analysing
• Summarising
• reporting
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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
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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)
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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
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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)
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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
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Planning a DatabaseDefine the purpose of the databaseDetermine the type of output reportsList all the data items (determines the fields)
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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
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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
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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
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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
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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
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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
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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
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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
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Field Name Data type Field size/length
Description
Sample database: Student file
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Features of Computerised DatabasesCreate fieldsAdd and alter recordsSearch for specific recordsSort recordsPrint reports
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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
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What is MS Access?An example of a DBMS which was
developed by Microsoft Corporation.
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Database Terms in AccessFields (columns)
Records (rows)
table – refers to a file in Access
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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
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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
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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
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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, =, >, <, <>, >=, <=)
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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
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Relational Database
Relational database links some tables with certain data common with other tables.
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Sources• Chapter 7 – Database Applications & Privacy
Implications, Tomorrow’s Technology and You (8th ed) by G. Beekman & M. Quinn