Databases

Databases: are permanent (persistent), Related, Organized and Usually stored for a organisation 

External view - what user sees, designed to be helpful for task

Conceptual view - how data is organised

Physical view - how data is actually stored

Flat file - single table, suitable for simple data requirements

Hierarchical - for when data relate to each other like branches on a tree

Serial file - one after the other, stored adjacently

Sequential - data stored in order of important keys values

Exam corrections

For question 2, it was bus topology because there was one linking cable connecting all the devices.

The device was a 

The functions are to share data between workstations, restrict data use for individual accounts

Internet

Internet: worldwide network of networks, use TCP/IP to control data exchange.

WWW: World Wide Web, is all the public web sites on the internet.

TCP/IP: Transmission Control Protocol - makes sure the correct data is delivered from client to server, detects error.  IP - moves data between networks.

Redundancy:   A backup system if something fails

Digital and analogue internet: was made of phone system so used analogue system, analogues have to be decoded so digital ones are better as they don't need to be decoded.

bandwidth:  speed of data transmission normally in bit rate

Broadband:  high speed data transmission that carries large amount of data at once through a cable.

Networks

LAN:

    Local area network, connected set of computers and other devices, each device is called a node.

    Advantages-

        Allows communication between workers, data sharing, sharing peripherals, upgrade easier,

        distributing processing.

    Disadvantages-

        Expertise needed to set up, strong passwords

    Hardware-

        NIC-network interface card, every node needs one to connect with LAN produce electrical signals

        HUB-a device that connects nodes together, makes them act as one unit, all data packets are                           transmitted

    A router forwards data packages between computer networks

    Switches allow nodes to communicate with each other 

    Wireless access point, means no building work needed, flexible, visitors can access but has a       

    Low performance and security issues.

Peer to peer:   Could be slow because of data collisions and shared processor power.

Client server:   One or more computers are the server and they have software, data and peripheral access that it shares, in control of what they can do, records what is used for, extra security and requires a log in.

Topology: physical layout of network

Star topology: shared link to a server, few data collisions, fast and can have independent sections.

Ring topology: all connected by one cable, fast and no collisions as one way traffic but any problems would affect all of them.

Bus topolgy: one linking cable with nodes coming of it, cheap but lots of data collision, slows down in heavy traffic, any problems affect all.

WAN: wide area network, structure could be telecoms companies

VPN: virtual private network, better security, uses Internet.

Protocols: rules for device communication

   DNS: translates domain names into IP adresses

   TS/SSL: secure communications

   FTP: copy files from another host

   Gopher: early way of searching on internet

   HTTP: for web pages

   IMAP: method for accessing emails

   POP3: another way to access emails

   Telnet: text communications on a network

IP adresses: code that identifies the node

MAC: communicate with physical layer of network

Packets: data is put into packets when it needs to go to another adress

Security

   Access levels: uses log in names to grant privileges

   Passwords: must be something that people couldn't guess and should be changed often

   Encryption

Policies: tell users what is expected from them

Questions

IDLE is useful for programmers because it does stuff like colouring bits of code depending on what it does to help you know if you have written it write so you can identify errors, also it tries to tell you errors when you write it.

Open source software is where the software is available for everyone.

Pros for using it include the fact that it is widely used and therefore tested and most bugs would be fixed, it is specifically modified to fit the purpose.

Cons for using it include possible low quality and no guarantee of support if it goes wrong.

Editors are where you write code, and it can do stuff such as colour bits of code depending on what it does, this make it easier for the person to write code in it.

Disk defragmenters sort out the memory, getting rid of gaps to make it more efficient and gain space, it is needed because when you delete and add files, slight gaps appear.

Firewalls exist to detect viruses and stop them and to stop us accidently going on dangerous websites.

They also stop information being stolen from you.

Off-the-shelf software is software written and sold by companies for a variety of tasks.

it is very cheap because the code is being sold to lots of people.

Software

3 main categories of software are:

Systems software  -  operating systems, device drivers, firmware, servers, utilities, interfaces

Development software  

Applications

Operating system ~ platform, a collecting if programs that control the hardware.

At the heart of the operating system is the kernel, the kernel looks after low level hardware operations.

       Running: what CPU is currently doing

       Runnable: waiting to run after what is running

       Waiting: waiting to join the queue 

GUI: graphical user interface

It uses icons (pictures) to represent resources and actions.

Main examples are Windows, MacOS, UNIX, LINUX

Device drivers tell your CPU to finish what it is doing as soon as possible and deal with peripheral devices.

Utility software deal with simple maintenance tasks

Disk defragmenters gets rid of gaps caused by deleting and adding files to improve access speeds.

Interpreters and compilers: both translate high level code into machine code (source code to object code) but interpreters do it 1 line at a time and execute it. 

Assemblers translate assembly languages (1 line is 1 machine instruction like LMC) into machine code.

Linkers link sub programs together. #look up examples

Off the shelf software

    Advantages-immediately available, well tested, cheap

    Disadvantages-may not meet exact requirements

Custom Written software

    Advantages-specifically written

    Disadvantages-expensive and takes time

Open source software

    Advantages-specifically modified, bugs fixed quickly

    Disadvantages-nobody owns it so no guaranteed support, issues with quality

Testing code

Errors can include syntax errors, where you spell I wrong or forget to declare variables before use.

Another is logical errors, such as division by zero, infinite loops.

To test it, identify suitable test data and an expected outcome.

Test data is valid for extreme end of acceptable inputs.

Test data is out of range and should be rejected.

Test data that is invalid but only just on the limit of being unacceptable.

Erroneous, wrong type of input.