Comp Fundamentals Unit 3

7/29/2019 Comp Fundamentals Unit 3

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Department of BCA Session: July 2008 Nov 2008 1/57

BCA103 - Computer Fundamentals

Computer software, or just software is a generalterm used to describe a collection of computerprograms, procedures and documentation that performsome tasks on a computer system.

What is Software?

Hardware is a general term that refers to thephysical artifacts of a technology. It may also meanthe physical components of a computer system, inthe form ofcomputer hardware.

What is Hardware?

A cultural artifact is a human-made object which

gives information about the culture of its creatorand users. The artifact may change over time inwhat it represents, how it appears and how and whyit is used as the culture changes over time.
http://en.wikipedia.org/wiki/Cultural_artifacthttp://en.wikipedia.org/wiki/Technologyhttp://en.wikipedia.org/wiki/Computer_systemhttp://en.wikipedia.org/wiki/Computer_hardwarehttp://en.wiktionary.org/wiki/objecthttp://en.wikipedia.org/wiki/Culturehttp://en.wikipedia.org/wiki/Culturehttp://en.wiktionary.org/wiki/objecthttp://en.wikipedia.org/wiki/Computer_hardwarehttp://en.wikipedia.org/wiki/Computer_systemhttp://en.wikipedia.org/wiki/Technologyhttp://en.wikipedia.org/wiki/Cultural_artifact


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Middleware is the enabling technology ofenterpriseapplication integration. It describes a piece ofsoftware that connects two or more softwareapplications, allowing them to exchange data.

System software is any computer software whichmanages and controls computer hardware so thatapplication software can perform a task

Application software is a subclass of computersoftware that employs the capabilities of a computerdirectly and thoroughly to a task that the user wishesto perform.

What is Application Software?

What is System Software?

What is Middleware?
http://en.wikipedia.org/wiki/Enterprise_application_integrationhttp://en.wikipedia.org/wiki/Enterprise_application_integrationhttp://en.wikipedia.org/wiki/Enterprise_application_integrationhttp://en.wikipedia.org/wiki/Enterprise_application_integration


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System software which is involved in integrating acomputer's various capabilities, but typically does notdirectly apply them in the performance of tasks that

benefit the user.

An electrical bulb is an application software.

Electric power generation plant is a system software.

What is computer programme?

A sequence of instructions written in a language thatcan be understood by the computer is called acomputer programme.

The software development is continuous process,where as hardware is a one time investment.


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Users

Application SoftwareSystem Software

Relationship between hardware to users.

Hardware

Examples of Application Software

Word Processing, Spreadsheets,Database Management Software

Graphics, multimedia, presentation software


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Service or Utility Software

File defragementation, Data compression

Backup software, data recovery software

Antivirus utility, screen savers.

System Software

TranslatorsCompilers, Assemblers, Interpreters

Operating system.

Operating system carries out variety of functions

Scheduling and loading, Resourcemanagement (memory,devices), Handlingerrors, CPU time management, MemoryManagement, communication with users.


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Types of Operating Systems

Batch Processing- is known as serial, sequential, off line or stacked

job processing.

- Reduces the idle time of a computer systembecause transition from one job to another doesnot require operator intervention.

It allows sharing of computer resources amongmany users and programs,

- Does not allows the priority scheduling.

Batch processing has been associated withmainframe computers since the earliest days of

electronic computing in 1950sBatch processing has grown beyond its mainframeorigins, and is now frequently used in UNIXenvironments and Microsoft Windows too.


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Multi-Tasking

Multitasking solves the problem by schedulingwhich task may be the one running at any giventime, and when another waiting task gets a turn.

In the case of a computer with a single CPU, onlyone task is said to be running at any point in time,meaning that the CPU is actively executinginstructions for that task.

The act of reassigning a CPU from one task toanother one is called a context switch.

Even on computers with more than one CPU,multitasking allows many more tasks to be runthan there are CPUs.
http://en.wikipedia.org/wiki/Scheduling_(computing)http://en.wikipedia.org/wiki/Context_switchhttp://en.wikipedia.org/wiki/Context_switchhttp://en.wikipedia.org/wiki/Scheduling_(computing)


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Multi-Processing- Two or more independent processors are linkedtogether in a coordinated system and instructionsfrom different and independent programs can beprocessed at the same instant in time by theprocessors.

- Many complex operations can be performed atthe same time.

- CPU can function on complementary units toprovide data and control for one another.

- Is used for major control applications such asrailroad control or airlines management.


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Multi Programming- Is executing two or more different andindependent programs by the same computer.

- Permits more than one job to utilize the CPU timeat any moment using scheduling technique.

- The OS picks up any of the programs asscheduled and starts execution.

Multiprogramming doesn't give any guarantee thata program will run in a timely manner.

- Is optimize the resource utilization of a computersystem and supports multiple users.

Indeed, the very first program may very well run for

hours without needing access to a peripheral


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Multi-ThreadingAs multitasking greatly improved the throughput ofcomputers, programmers started to implementapplications as sets of cooperating processes (e.g.one process gathering input data, one processprocessing input data, one process writing out results

on disk.)

Thus, threads are basically processes that run in

the same memory context.

Threads were born from the idea that the mostefficient way for cooperating processes to exchangedata would be to share their entire memory space

Threads are described as lightweightbecauseswitching between threads does not involvechanging the memory context.
http://en.wikipedia.org/wiki/Thread_(computer_science)http://en.wikipedia.org/wiki/Thread_(computer_science)


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Multi-ThreadingWhile threads are scheduled preemptively, someoperating systems provide a variant to threads,named fibers, that are scheduled cooperatively

Fibers are even more lightweight than threads

The simultaneous use of more than one CPU toexecute a program. Ideally, parallel processingmakes a program run faster because there are more

engines (CPUs) running it.

Parallel processing

separate CPUs can execute different portions withoutinterfering with each other.
http://en.wikipedia.org/wiki/Fiber_(computer_science)http://www.webopedia.com/TERM/P/execute.htmlhttp://www.webopedia.com/TERM/P/program.htmlhttp://www.webopedia.com/TERM/P/run.htmlhttp://www.webopedia.com/TERM/P/run.htmlhttp://www.webopedia.com/TERM/P/program.htmlhttp://www.webopedia.com/TERM/P/execute.htmlhttp://en.wikipedia.org/wiki/Fiber_(computer_science)


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Online processingIt is a system that operates in an interactive modewith quick response time.

On line processing systems perform random andrapid input of transactions and provide immediate

access to the records.

operational deadlines from event to system response

Real time processing

By contrast, a non-real-time system is one for whichthere is no deadline, even if fast response or high

performance is desired or even preferred

The anti-lock brakes on a car are a simple exampleof a real-time computing system
http://en.wikipedia.org/wiki/Anti-lock_brakeshttp://en.wikipedia.org/wiki/Anti-lock_brakeshttp://en.wikipedia.org/wiki/Anti-lock_brakeshttp://en.wikipedia.org/wiki/Anti-lock_brakes


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http://upload.wikimedia.org/wikipedia/commons/9/9d/ABS-Sensor.jpg


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Virus and Anti-virus

VirusA computer virus is a computer program that cancopy itself and infect a computer without permissionor knowledge of the user.

The original virus may modify the copies, or thecopies may modify themselves

A virus can only spread from one computer toanother when its host is taken to the uninfectedcomputer

Viruses are sometimes confused with computerworms and Trojan horses

A computer worm is a self-replicating computerprogram.
http://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_wormhttp://en.wikipedia.org/wiki/Computer_wormhttp://en.wikipedia.org/wiki/Trojan_Horse_(Computing)http://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Trojan_Horse_(Computing)http://en.wikipedia.org/wiki/Computer_wormhttp://en.wikipedia.org/wiki/Computer_wormhttp://en.wikipedia.org/wiki/Computer_program


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VirusWorms almost always cause harm to the network, ifonly by consuming bandwidth, whereas virusesalmost always corrupt or modify files on a targetedcomputer.

Bandwidth (computing): a rate of data transfer, orbit rate, measured in bits per second

a Trojan horse, also known as a trojan, is malwarethat appears to perform a desirable function but infact performs undisclosed malicious functions.Therefore, a computer worm or virus may be aTrojan horse.

In general, a worm does not actually harm either thesystem's hardware or software.
http://en.wikipedia.org/wiki/Malwarehttp://en.wikipedia.org/wiki/Malware


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Residents Virus

Nonresident viruses can be thought of as consistingof a finder module and a replication module. Thefinder module is responsible for finding new files toinfect. For each new executable file the finder moduleencounters, it calls the replication module to infect

that file.

The virus loads the replication module into memorywhen it is executed and ensures that this module isexecuted each time the operating system is called to

perform a certain operation

Non-residents Virus

In this case, the virus infects every suitable programthat is executed on the computer.


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Most modern antivirus software is now designed tocombat a wide range of threats, including worms,phishing attacks, rootkits, trojan horses and othermalware

Antivirus software are computer programs thatattempt to identify, neutralize or eliminate malicioussoftware

In computing, phishing is the criminallyfraudulentprocess of attempting to acquire sensitive

information such as usernames, passwords and creditcard details, by masquerading as a trustworthy entityin an electronic communication.

Anti-Virus
http://en.wikipedia.org/wiki/Computer_wormhttp://en.wikipedia.org/wiki/Phishinghttp://en.wikipedia.org/wiki/Rootkithttp://en.wikipedia.org/wiki/Trojan_horse_(computing)http://en.wikipedia.org/wiki/Malwarehttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Malicious_softwarehttp://en.wikipedia.org/wiki/Malicious_softwarehttp://en.wikipedia.org/wiki/Computinghttp://en.wikipedia.org/wiki/Criminalhttp://en.wikipedia.org/wiki/Fraudhttp://en.wikipedia.org/wiki/Passwordhttp://en.wikipedia.org/wiki/Passwordhttp://en.wikipedia.org/wiki/Fraudhttp://en.wikipedia.org/wiki/Criminalhttp://en.wikipedia.org/wiki/Computinghttp://en.wikipedia.org/wiki/Malicious_softwarehttp://en.wikipedia.org/wiki/Malicious_softwarehttp://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Malwarehttp://en.wikipedia.org/wiki/Trojan_horse_(computing)http://en.wikipedia.org/wiki/Rootkithttp://en.wikipedia.org/wiki/Phishinghttp://en.wikipedia.org/wiki/Computer_worm


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A rootkit is a program (or combination of severalprograms) designed to take fundamental control (inUnix terms "root" access, in Windows "Administrator"access) of a computer system, without authorizationby the system's owners and legitimate managers

Antivirus software typically uses two differentapproaches to identify virus:

1. examining (scanning) files to look for knownviruses matching definitions in a virus dictionary, and

2. identifying suspicious behavior from any computerprogram which might indicate infection

Anti-Virus
http://en.wikipedia.org/wiki/Computer_programhttp://en.wikipedia.org/wiki/Unixhttp://en.wikipedia.org/wiki/Microsoft_Windowshttp://en.wikipedia.org/wiki/Computer_filehttp://en.wikipedia.org/wiki/Computer_filehttp://en.wikipedia.org/wiki/Microsoft_Windowshttp://en.wikipedia.org/wiki/Unixhttp://en.wikipedia.org/wiki/Computer_program


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The suspicious behavior approach, by contrast,doesn't attempt to identify known viruses, butinstead monitors the behavior of all programs.

If one program tries to write data to an executable

program, for example, the antivirus software can flagthis suspicious behavior, alert a user, and ask what todo.

Unlike the dictionary approach, the suspiciousbehavior approach therefore provides protection

against brand-new viruses that do not yet exist inany virus dictionaries

Anti-Virus
http://en.wikipedia.org/wiki/Zero_day_virushttp://en.wikipedia.org/wiki/Zero_day_virushttp://en.wikipedia.org/wiki/Zero_day_virushttp://en.wikipedia.org/wiki/Zero_day_virus


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Other approachesSome antivirus software use other types ofheuristic analysis.For example, it could try to emulate the beginning of the codeof each new executable that the system invokes beforetransferring control to that executable. If the program seemsto use self-modifying code or otherwise appears as a virus

However, this method could result in a lot of false positives.

Yet another detection method involves using a sandbox. Asandbox emulates the operating system and runs theexecutable in this simulation. After the program hasterminated, software analyzes the sandbox for any changeswhich might indicate a virus.

Also this method may fail as viruses can be nondeterministic so it will be impossible to detect it from one run.

Some virus scanners can also warn a user if a file is likely tocontain a virus based on the file type.
http://en.wikipedia.org/wiki/Heuristic_(computer_science)http://en.wikipedia.org/wiki/Self-modifying_codehttp://en.wikipedia.org/wiki/Sandbox_(computer_security)http://en.wikipedia.org/wiki/Nondeterministic_algorithmhttp://en.wikipedia.org/wiki/File_typehttp://en.wikipedia.org/wiki/File_typehttp://en.wikipedia.org/wiki/Nondeterministic_algorithmhttp://en.wikipedia.org/wiki/Sandbox_(computer_security)http://en.wikipedia.org/wiki/Self-modifying_codehttp://en.wikipedia.org/wiki/Self-modifying_codehttp://en.wikipedia.org/wiki/Self-modifying_codehttp://en.wikipedia.org/wiki/Heuristic_(computer_science)


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Computers SecurityThe computers security starts with a good virusscanner and never ends.

Typical approaches to improving computer securitycan include the following:1. Physically limit access to computers to only those

who will not compromise security.2. Hardware mechanisms that impose rules oncomputer programs, thus avoiding depending oncomputer programs for computer security.3. Operating system mechanisms that impose ruleson programs to avoid trusting computer programs.

A firewall is a device or set of devices configured topermit, deny, encrypt, decrypt, or proxy all computertraffic between different security domains based upona set of rules and other criteria.


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Machine and high level languages

Programming languages are said to be lower orhigher, depending on whether they are closer to thelanguage the computer itself uses or to the languagethat people use.

Here we will consider five levels (or generations) oflanguages:

1. Machine languages/1st generations2. Assembly languages / 2nd generations3. Procedural languages / 3rd generations4. Problem-oriented / 4th generations5. Natural languages / 5th generations

The closer the level is to human speech, the more it is

described as a user friendly language.


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Machine languagesComputers are working two-state system, that is,on/off or yes/no.

In the early days of computers, with machines as theENIAC, which used vacuum tubes, one could actuallysee the tubes lit up or unlit (dark), corresponding to

the 1/0 binary stat the switch was either on or off.

In addition, in those early days there was no suchthing as software. There was only hardware withelectrical on/off switches.

Whenever a program was to be run, all the switches

had to be set sometimes as many as 6,000 switchesfor a single program.Then next program the switches had to be reset, aprocess that might take weeks.


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Machine languagesAdvantage: execution is very fast and efficientbecause the computer can accept the machine codeas it is.

Disadvantage:1. there is no standard machine language2. The language are machine dependent.

Also called symbolic language or abbreviated ormnemonic code.Code are easily memorized replacing 0s and 1s of

machine language.

Assembly languages

Actually, assembly language do not replace machinelanguages.


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The assembly languages code is very similar in formto machine language.

In fact, the first assembly languages had a one-to-one correspondence. That is, 20 assembly statementswould be translated into 20 machine statements.

Assembly languages

Advantage:1. standardized and easier to use than machinelanguage.2. Easier to debug because programs locate andidentify syntax errors.3. Operate very efficiently but not as efficient as themachine language.

Disadvantage:1. Still complex to code.2. Again machine dependent.3. Usually very long.


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Assisted programmers by reducing further thenumber of computer operation details they had tospecify, so that concentrate more on the logic neededto solve the problem.

High level languages

The term "high-level language" does not imply that thelanguage is always superior to low-level programminglanguages - in fact, in terms of the depth of knowledge ofhow computers work required to productively program in agiven language, the inverse may be true.

high-level languages make complex programmingsimpler, while low-level languages tend to producemore efficient code

For this reason, code which needs to run particularlyquickly and efficiently may be written in a lower-levellanguage, even if a higher-level language would makethe coding easier.
http://en.wikipedia.org/wiki/Low-level_programming_languagehttp://en.wikipedia.org/wiki/Low-level_programming_languagehttp://en.wikipedia.org/wiki/Low-level_programming_languagehttp://en.wikipedia.org/wiki/Low-level_programming_languagehttp://en.wikipedia.org/wiki/Low-level_programming_languagehttp://en.wikipedia.org/wiki/Low-level_programming_language


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Procedural-oriented languageProblem-oriented language (BASIC, Pascal)Natural language

Types of High level languages

In a procedural-based programming language, aprogrammer writes out instructions that are followed

by a computer from start to finish.Example: c, c++, Basic, COBOL

Non procedural also called "declarative language,"users concentrate on defining the input and outputrather than the program steps required in aprocedural language such as C++, COBOL.

Query languages, report writers, interactive databaseprograms, spreadsheets and application generatorsare examples of non-procedural languages.


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MS DOS and Window OS

MSDOS is a single user operating system andtherefore all the resources are available to this user.

MS DOS

DOS contains three files:1. IO.SYS,2. MSDOS.SYS

3. Command.com

1. IO.SYSa) It verifies the input output devices and drivers.b) loads the file MSDOS.SYS from the hard disk

into memory.

2. MSDOS.SYSit is also called DOS Kernel.it is a link between BIOS and users applicationprograms.


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MS DOSMSDOS has four important functions as:1. Process Control2. Memory management3. Application Program Interface (API)4. File Management System (FMS)

Process Control:Does the management of the program that is being

executedLoads program into the memory and initiates

execution of loaded program.

It also recovers the system files when programexecution is terminated in between.


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Memory ManagementAllocates the memory to different application

programs.It also does file allocation according to memory

demand.

Application Program Interface:Works like an intelligent agent so that every program

is allotted to the various hardware devices.

File management system:Is the largest portion of the MSDOS.SYS.

It can read, write display and print the files.It can rename, copy and remove the files.


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Command.comHas two portions as:

a) Resident portion. b) Transient portion.

Resident portion:

Contains internal commands in it.System can only be interrupted by using Ctrl+C incase of any execution error for job termination.

It displays the error message likeBad command or file nameAbort, Retry, Ignore?

It contains code required to reload the transientportion (external command) of command.com.


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MS DOS and Window OSTransient portion:It is the temporary portion of command.com.Any application program has shortage of memory

space, then transient portion is erased andmemory space is made available to applicationprogram.

When an application program is not in use orterminated, then it reload the erased portion.It displays dos prompt like A:/>, B:/>.

Booting:Can be defined loading of set of programs from the

ROM into RAM so that it creates an environment

for the execution of commands or furtherprocessing.

The loadable files are IO.SYS, MSDOS.SYS,Command.com


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MS DOS and Window OSWhile Booting:ROM startup routines set up addresses of ROM-BIOS

routines Interrupt Vector Table (IVT) at the lowend of memory.

RAM testROM startup routines check for standard and non-

standard equipment attached to computer.ROM startup routines reads from BIOS.For example,First attempt of booting from A:/> then C:/>

Types of Booting:Cold Booting: when we switched on. Slow in process.Hot Booting: when we press Reset button. Faster

than cold booting because it will not restartcomputer instead reload the files.


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MS DOS and Window OSInternal CommandsCLS DATE TIME VOLUME TIME VERCOPYCON TYPE REN DEL MD CDRD PATH COPY PROMPT

DIR DIR/P DIR/W DIR/S DIR with wildcard(*,?)

External Commands:EDIT to edit existing file.ATTRIB to change the attributes of files

example. +R read only, -R remove read only+H to hide -H to remove hide attribute

BACKUP create a copy to destination pathRESTORE copy the files in original pathCHKDSK DISKCOPY DELTREEFORMAT FDISK MOVE PRINT UNDELETE


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Database Management Systems

Information is the backbone of any organization.

What is information?Information is nothing but refined data, data that

have been put into a meaningful and usefulcontext and communicated to a recipient who

used it to make decisions.

Quality of InformationAccuracy:- means that information is free from mistakes and

errors

- Means that information is free from bias.- Manipulated information is worse than no

information.


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Quality of InformationTimeliness:- Means that getting the information to the

recipients within the needed time frame.- Breaking news

Relevancy:- Means the use of a piece of information for a

particular person.- Subjective matter.

What is Database?

A database consists ofdata, relationships, constraintsand schema.

- Data are binary computer representations ofstored logical entities.


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- Relationships represent a correspondence betweenthe various data elements.- Constraints are predicates that define the correct

database states where the scheme describes theorganization of data and relationships within thedatabase

- The schema defines the various views of thedatabase for database management systemcomponents use and for applications security.

Database- A collection of data designed to be used by

different people is called database.- The data are stored in such a fashion that they areindependent of the programs of people using thedata.


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Database Management SystemsWhy integrated database

- Data redundancyeach department has its own private files resultingstorage space is wasted. Hence the redundancycan be controlled.

- Data inconsistencyif a database is updated and not reflected in otherdepartment becomes data inconsistency.

- Integritymeans that the data in the database is accurate.

- Conflicting requirementsknowing the overall requirements as opposed to

the individual requirement, the database can bestructured to provide an overall service that isbest for the organization


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Database Management SystemsCharacteristics of data in a database

- Shareddata in a database are shared among differentusers and applications.

- Persistencethe data can live beyond the scope of the processthat created it.

- Validity: data should be correct with respect to thereal world.

- Security: data should be protected fromunauthorized access.

- Independent

the three levels in the schema (internal,conceptual and external) should be independent ofeach other so that the changes in the schema atone level should not affect the other levels.


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Database Management SystemsDatabase Management System

- A database management system (DBMS) is asoftware that provides services for accessing adatabase, while maintaining all the requiredfeature of the data.

Transaction processing

- Is a sequence is database operations thatrepresents a logical unit of work. It access adatabase and transforms it from one state toanother.

- It may be update, delete, modify etc.,

Concurrency management

- Is the database management activity ofcoordinating the actions of database manipulationprocess that operate concurrently, access shareddata and can potentially interfere with each other.


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Database Management SystemsRecovery

- Recovery mechanisms of a DBMS make sure thatthe database is returned to a consistent stateafter a transaction fails or aborts.

- Recovery is very much related to concurrency inthe sense that the more the concurrency, themore is the chance of an aborted transaction canaffecting many other transactions.

security- The level of access for each user and the

operations that each user can perform on the datawill be monitored and controlled by the DBMS

depending on the access privileges of the users.Language interface- Provides the definition and manipulation of the

data in the database. Ex DDL, DML


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Types of Database Management SystemsHierarchical Model

- Oldest database models (1950).- The hierarchical model assumes that a tree

structure is the most frequently occurringrelationship.

- This mislead restrictive view of relationships.

Network Model- Replaces the hierarchical tree with a graph thus

allowing more general connections among thenodes.

- A strict hierarchical arrangement is not possiblewhen an employee works for two departments,

then the tree will become graph.- In hierarchical model we have to place a data

simultaneously in two location in the list. Innetwork we can connect.


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Types of Database Management SystemsRelational Model

- The relational model uses tables to organize thedata elements. Each table corresponds to anapplication entity, and each row represents aninstance of that entity.

- For example , book database is an entity,- a book detail is an instance.

Object-oriented Model- OOM represents an entity as a class.- A class represents both object attributes as well

as the behavior of the entity.- For example, a book class will have not only the

book attributes (ISBN, Tile, Price) but alsoprocedure that imitate actions expected(updateprice()) of a book.


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Levels of database servicesPhysical Level

- At the lowest level, certain physical componentsorganize and store the raw data.

- In addition to hardware, these components includecontrol structures that track the location andformat of the stored data elements.

- Example: Buffer

- The physical layer typically has parameters thatcan be tuned for optimal performance under theaccess pattern of an applications.

- However in case of relation, object-orienteddatabase models, the tuning task is usually left tothe DBMS.


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Levels of database servicesConceptual Level

- Is isolating the data storage details to the physicallevel of DBMS, provides a convenientenvironment.

- The application objects exist at this level.Ex., Tables, views, triggers

- If the underlying hardware and OS changes, theconsequences limited to the interface between thephysical and conceptual layer.

- For example, OS is changed from UNIX to window,a new version of DBMS might be necessary.


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Levels of database servicesExternal Level

- Outer most layer- Different type of external views can use the same

conceptual view to satisfy the differing needs ofthe different users.

- The decoupling of the external and conceptuallevel is called logical data independence.

Database Design- A data base about a person may be consists of- Photograph, fingerprint, retina images- Name, age, sex, height, weight, address- Telephone number, blood, caste, religion, etc.,

Now the question is how much information about anentity should be collected.


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Database DesignData Normalization

- Normalization is the process of building databasestructures to store data.

- Data normalization is a corner stone of a relationaltheory.

- The different steps involved in data normalizationare called the normal forms.

- Each normal form builds upon the last version.

Keys- A key uniquely identifies a row in a table.Intelligent Keys- An intelligent key is based upon data values such

as a date, price, name.Non-Intelligent Keys- Is completely arbitrary, having no function or

meaning other than identification or a row.


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Database DesignIntelligent Keys

- Is problematic because the key value must bechanged to reflect changing data values.

- For example, price is changed, all related tablesmust be updated every time the key is updated.

Primary Keys- Is column in the table whose purpose is to

uniquely identify records from the same table.

Foreign Keys- A foreign key is a column in a table that uniquely

identifies the records from a different table.or

- The foreign key identifies a column or a set ofcolumns in one (referencing) table that refers to acolumn or set of columns in another (referenced)table


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Relationship

One-to-one- 1 to 1 relationships are rare, because data

elements related in this way are normally placedin the same table

One-to-many- When one data item can be linked to 0, 1 or many

other data items, you are dealing with a one-to-many relationship

- The same applies to the relationship that existsbetween a woman and her children. A woman can

have 0, 1 or many children and each child has onewoman as its mother.


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Relationship

Many-to-many- The many-to-many relationship is a relationship

where multiple rows from table A can correspond tomultiple rows in table B.

- An example of such a relationship is a school whereteachers teach students. In most schools each

teacher can teach multiple students and eachstudent can be taught by multiple teachers.- This relationships are problematic.- Normally this relationship expresses using

intersectiontables.- An intersection table contains two or more foreign

keys, relating the primary key values of two ormore tables to each other.

- The role of an intersection table is to convert manyto many into one-to-many.


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Normalization

- The guidelines for proper relational database designare laid out in the relational model. They aregrouped into 5 groups called "normalforms".

- The first normal form represents the lowest form ofdatabase normalization, the fifth represents thehighest form of database normalization.

- These normal forms are guidelines for gooddatabase design.- You are not obliged to adhere to all fivenormal

forms when designing a database.

- Nevertheless, you are advised to normalize you

database to some extent, because normalizationhas some significantadvantages in terms of theefficiency and maintainability of your database.


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Normalization

Whynormalization- Complex queries can be done using simple SQL

commands.

- Data Integrity.data integrity means that the data values in the

database are correct and consistent.

- Avoids data redundant

- Scalability.Scalability is the ability to meet with future growth

demands


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Normalization

The first normal form (1NF)A database table is a representation of an "entity" in

the system you are building.Examples of entities are order, customer, contact

moment, product, etc.Each row in the database table represents one

occurrence of an entity. For example in a customertable each row will contain information about 1customer.

Each table has a primary key, consisting of thesmallest possible number of fields.

Atomicity: each field contains one value. An adres forexample, would ideally be stored in three separatefields: number, street, city.


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Normalization

The second normal form (2NF)The second normal deals with data redundancy. The

rules comprised in the second normal form are asfollows.

The database fullfills all the requirements of thefirst normal form

All non-primary-key fields in a table must be fullydependent on the entire primary key of the table

The third normal form (3NF) Already meet the requirements of both 1NF and

2NF

Remove columns that are not fully dependent uponthe primary key.
http://databases.about.com/od/specificproducts/l/aa1nf.htmhttp://databases.about.com/od/specificproducts/a/2nf.htmhttp://databases.about.com/library/glossary/bldef-column.htmhttp://databases.about.com/library/glossary/bldef-primarykey.htmhttp://databases.about.com/library/glossary/bldef-primarykey.htmhttp://databases.about.com/library/glossary/bldef-column.htmhttp://databases.about.com/od/specificproducts/a/2nf.htmhttp://databases.about.com/od/specificproducts/l/aa1nf.htm


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Normalization

For example, we will normalize following fields:Order NumberCustomer NumberUnit PriceQuantityTotal

Remember, our first requirement is that the table mustsatisfy the requirements of1NF and 2NF.Are there any duplicative columns?No.Do we have a primary key?Yes, the order number. Therefore, we satisfy the

requirements of 1NF.Are there any subsets of data that apply to multiple

rows? No, so we also satisfy the requirements of2NF.


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Normalization

Now, are all of the columns fully dependent upon theprimary key? The customer number varies with theorder number and it doesn't appear to depend uponany of the other fields.

What about the unit price? This field could be

dependent upon the customer number in a situationwhere we charged each customer a set price.

However, looking at the data above, it appears wesometimes charge the same customer differentprices. Therefore, the unit price is fully dependent

upon the order number.

The quantity of items also varies from order to order,so we're OK there.


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What about the total? It looks like we might be in

trouble here. The total can be derived bymultiplying the unit price by the quantity, thereforeit is not fully dependent upon the primary key. Wemust remove it from the table to comply with thethird normal form.

Perhaps we use the following attributes:

Order number

Customer number

Unit price

Quantity

Now our table is in 3NF. But you might ask, whatabout total? This is a derived field and it is best notto store it in the database at all. We can computeit.

Documents

Comp Fundamentals Unit 3