Monday, March 9, 2015

Is it valid or allowed, can check if something is valid but sometime inacurrate
You can check if it is not correct.
This ensure data is correctly inputted and spots human errors.
Ensures data entered complies with allowable data
many different types of validation include:

Range checks
format check
type character checks presence checks
Length checks
Lookup existence.

Is it the same?

Hesitance check
It is a number that is derived from the other contents of the number

Backing up and archivivng
full compies every file fully]
Incremental Backup
Only copies files that are changed in the last backup

not the same as backup

storing old/unused data

Taking it from server mainframe

Transferring onto storage medium

Unlikely to be used again but still available.

Syntax error

  • Missing extra brackets
  • Using variables
  • Brackets not used properly
  • The statement in the code does not follow the rules of the language.
  • Usually detected by the translator, as the statement cannot be understood.
  • Programs will not be compiled
Logic Error
  • The syntax of the code is correct
  • the code does not do what it should
  • Will usually run normally but with some unexpected result
  • Usually tested while being tested
  • Incorrect mathematical formulae
  • Misplaced brackets
  • Instruction written and therefore executed in the wrong order
Run time error
  • The syntax is correct
  • the logic of the program is correct
  • extreme circumstances cause crash
  • program attempts impossible operation
  • causes program to crash at run time
  • usually detected while testing
  • Division by zero
  • attempt to access non existent file
  • attempt to reference array elements before they are initialised 
Test Data
Data which syhold genarate an error message 

OSI Model

A set of rules that govern how something works.
Within a computer science:
  • A communication protocol is a system of digital rules for data exchange within or between computers
  • When data is exchanged through a computer network, the rules system is called a network protocol 
Logical Protocol (SMTP) - It is how emails are sent

  • HTTPS - Browsing through the net 

  • TSP

  • Bluetooth
  • Wifi
Lowest layer is logical and the highest is physical.

Physical layer = Describes electrical and physical specifications for devices: Cable, connectors, hubs.

Data link layer = Provides connections between hosts on the same network: Ethernet 

Network layer =  Provides connection between hosts on different networks :IPv4 and IPv6. Routing of packets.

Transport = Provides transport of data: TCP and UDP. End to end connections.

Session =  establishing a connection. Controls the dialogs between computers (handshake). Also controls duplexing termination and restarts. 

Presentation = compressing the data.  Provides a context for communication between layers 
ASCII Characters, Encryption and decryption. Compression.

Application = HTTPS, where we find network application eg mail, browser 
  • All
  • People
  • Studying
  • This 
  • Needs
  • Drastic
  • Psychotherapy

It hands communication between computers across networks.

Global and Local Variables


  • The scope of a declaration is the block of code where the identifier is valid for use

  • A global declaration is made outside the bodies of all function and outside the main program. it is normally grouped with the other global declarations and places at the beginning of the the program file.
  • Local declaration is one that is made inside the body of a function. locally declared variables cannot be accessed outside of the function they were declared in
  • It is possible to declare the same identifier name is different parts of the program.

Local Variables

  • We have used thus have been local variables
  • A Local variable is a variable which is either a variable declared within the function.
  • As you may have encountered in your programming if we declare variables in function then we can only use them within that function. This is a direct result of placing our declaration statements inside functions.

Global variable

  • A global variable def is a variable which is accessible in multiple scopes
  • It is important to note that global variables are only accessible after they have been declared.
  • Undisciplined use of global variables may lead to confusion and debugging difficulties.
  • Instead of using global variable in function, try passing local variables  by reference.