FORM 2 COMPUTING PROMOTIONAL EXAMINATIONS
THEORY
COMPUTER NETWORKS
A network is a series of computer systems that are linked together so that they are able to share computer power and storage facilities.
A computer network can be divided into a small segment called a Local Area Network (LAN), a networking between computers in a building or an office, Medium Sized Networks (MAN), are communication between two offices in a city, and Wide Area Networks (WAN), is networking between the computers, one is locally placed and the others can be thousands away, in another city or another country.
WAN Connectivity is achieved by a device known as “Router”. The internet is the world’s largest WAN, where millions of computers from all over the globe are connected with each other.
Networking is the practice of linking two or more computers and devices with each other. The connectivity can be wired or wireless. A computer network can be categorized in different ways, depending on the geographical area as mentioned above.
There are two main types of computer networking; client-server and peer-to-peer. In the client server networking, a computer plays a major role known as a server, where the files, data in the form of web pages, documents or spread file sheets, video, database & resources are placed.
All the other computers in the client/server networks are called clients and they get the data from the server.
In the peer-to-peer networks, all the computers play the same role and no computer acts as a centralized server. In the major businesses around the world the client-server network model is in major use.
A network topology defines the structure, design and layout of a network. There are different topologies like bus, ring, star, mesh, hybrid, etc. The star topology is the most commonly used topology. In the star topology, all the computers in the network are connected to a centralized device such as a HUB or a Switch, thus forming a star like structure. If the HUB or Switch fails to work for any reason then all the connectivity and communication between the computers will be halted.
A common communication language is used by the computers and the communication devices are known as protocols. The most commonly used and popular protocol on the internet and in homes and other networks is called TCP/IP. TCP/IP is not a single protocol but it is a suite of several protocols.
A computer network can be a wired or wireless and TCP/IP protocol can work in both types of network.
Network Topology
Physical Topology means the physical design of a network including the devices, location and cable installation.
Logical topology refers to the fact that how data actually transfers in a network as opposed to its design.
Topology can be considered as a virtual shape or structure of a network. This shape actually does not correspond to the actual physical design of the devices on the computer network. The computers on the home network can be arranged in a circle shape but it does not necessarily mean that it presents a ring topology. Computer networks can be categorized in the following categories:
· Bus
· Star
· Ring
· Mesh
Hybrid networks are the complex networks, which can be built of two or more of the above mentioned topologies.
Hybrid networks are the complex networks, which can be built of two or more of the above mentioned topologies.
Bus Topology
Bus topology uses a common backbone to connect all the network devices in a network in a linear shape. A single cable functions as the shared communication medium for all the devices attached with this cable with an interface connector. The device which wants to communicate sends the broadcast message to all the devices attached with the shared cable but only the intended recipient actually accepts and processes that message.
Ethernet bus topologies are easy to install and don’t require much cabling and only a main shared cable is used for network communication. 10Base-2 and 10BaseT are two popular types of Ethernet cables used in the Bus Topology. Also, Bus networks work with very limited devices. Performance issues are likely to occur in the Bus topology if more than 12 – 15 computers are added in a Bus network. Additionally, if the backbone cable fails then the whole network becomes useless and no communication fails among the computers. Unlike in the Star Topology in which if one computer is detached from a network then there is no effect on the other computers in a network.
Ring Topology
In a Ring Network, every computer or device has two adjacent neighbours for communication. In a ring network, all the communication messages travel in the same direction whether clockwise or anti-clockwise. Any damage of the cable of any cable or device can result in the breakdown of the whole network. Ring topology now has become obsolete.
Star Topology
In the computer networking world the most commonly used topology in LAN is the star topology. Star topologies can be implemented in homes, offices or even in a building. All the computers in the star topologies are connected to central devices like a HUB, Switch or Router. The functionality of all these devices is different. Computers in a network are usually connected with the HUB, Switch or Router with the Unshielded Twisted Pair (UTP) or Shielded Twisted Pair Cables.
As compared to the bus topology, a star network requires more devices & cables to complete a network. The failure of each node or cable in a star network won’t take down the entire network.
However if the central connecting device, such as the HUB, Switch or Router fails due to any reason, then ultimately the whole network can come down or collapse.
A dumb terminal in computing refers to a computer terminal that has limited functionality relative to other types of “smart” or intelligent computer terminals.
Intelligent Terminal: This is a terminal with its own processor that can take some of the processing load away from the main computer.
Gateway: This is a piece of software which translates data from one form of signal to another.
TCP/IP: This stands for Transmission Control Protocol/ Internet Protocol
Distributed System: This is a network system where several smaller machines are connected together, and each of them being used for a different task.
Advantages of network computers
a) For ease of communication between remote sites
b) For increasing speed of communication
c) For enabling access to more information quickly
d) For sharing expensive resources such as colour printers
CHECKING DATA
Reasons for Errors
Computers can produce accurate results (e.g. payslips, bills, invoices, etc.) only if the data put in them is accurate. In many systems an input document may be used and the data on the documents keyed into the computer. In other systems, this document is input directly to the computer, thus avoiding the need for typing which frequently introduces errors. Incorrect data can have serious or not so serious consequences.
Consequences of Errors
1. Customers become angry if they are sent bills that are too large, or companies lose money if bills are too small.
2. Wrong decisions made by man angers, because the decisions are based on wrong information.
3. A company could be prosecuted under the Data Protection Act, 1999, if the incorrect information causes the person concerned some kind of loss. For instance, if someone lost a job because a computer contained wrong information about a criminal record, the unsuccessful application could claim compensation.
HOW ARE ERRORS AVOIDED
Verification
Verification involves checking that what is on the input documents is exactly the same as what is entered into the computer. Notice that this does not mean that it is correct, since the details on the form could not be incorrect as in the example mentioned above.
One method of verification involves two people typing the same data and only if the data is identical it is accepted for further processing. This is often called double entry. The problem with double entry is that two people need to be paid for doing the same job. Also, although it is unlikely, they may both make identical errors so the mistake still goes unnoticed. Another method involves carefully checking what has been typed in against what was on the original document. This is called Proof Reading.
Validation
Validation is the process of detecting any data that is inaccurate, incomplete or unreasonable. Validation if performed by a computer problem. There are many ways that a computer can check to see whether the data is valid. (i.e. allowances).
Validation programs will usually perform some or all of the following types of checks:-
Character type checks Character type checks make sure that the right types of characters have been entered. Such checks detect numbers where characters should have been entered and vice versa.
Range checks Range checks are performed on a number to make sure that they lie within a specific range. If, for instance, a program deals with retirement pensions and all the receptions of the pensions have to be 60 or over, then if a typist enters 18 instead of 81, a range check would detect this. However, only absurd data may be detected, so if the typist enters 69 instead of 96, the range check would not detect this.
Presence check When entering data into a database, the completion of some fields may be optional. For example, a field set up so that a telephone number can be entered in a personal database, may not always have data in it as the person to which the fields refers may not have a telephone.
There are certain fields which must contain data in it and the system will not allow them to remain blank. An example of this would be a National Insurance Number in a payroll system.
Types of Errors
Transcription errors Transcription errors occur due to misreading or mistyping data. This may be caused by bad handwriting or confusing, for instance, the number 5 with the letter S, or 0 with the letter O.
Transposition errors Transposition errors occur when two digits or letters are swapped around. If you are typing in data in a high speed you do not always look at the screen and it is very usual that you will end up typing ‘ot’ instead of ‘to’, or ‘5124’ instead of ‘5214’. It is estimated that 70% of all errors are transposition errors.
HOW DATA IS STORED
Databases
A database is an organized collection of information or data. Putting information into a computer database gives you far more flexibility in organizing, displaying and printing that information.
The Parts of a Database
Files Think of a box of filtering cards, like those sometimes used in libraries. A computer’s equivalent to the complete box is a file. The computer’s file is usually stored on a disk, which may be optical or magnetic.
Records Within the library card box are the individual cards, each of which contains information about one book. In a computer database, the cards are known as records and most databases will display one record on the screen at a time, just as if you were browsing through the cards in a card box.
Fields On each card will be a number of different items if information: a library card might list the title, author, publisher, and ISBN (a unique number for a particular book). Each item of information on the computer records is known as a field, and it consists of two parts: the field name and the field data. The field names are the words, ‘Title’, ‘Author’ or ‘Publisher’. They are the same on each record and indicate what field data represents.
Record design Modern databases gives you freedom to design your own records. They give you an empty screen on which you can add the field names, fields and other background text such as the title.
Some databases require you to create a different type of field for different information. You usually have to specify the type of data to go into the field. This can be:
1. Numeric which means it contains only numbers. Make sure that a number does not have any starting zeros or dashes (e.g. A telephone number 0181-888-3456)
2. Character text, which means that numbers, letters and other symbols, can be entered.
3. Date, which means that the date is entered like this: 09/10/96
4. Logical, which allows Y/N (for Yes/No) or T/F (for True/False)
Key Fields
A key field is a field that may be used to search a file. It is always useful to the one field which is unique to a particular record.
Manual filing systems
The main problems arise in the information situation:
1. We may need to obtain information that is held on several files. Suppose we wanted to find out the name of system analysts, with fewer than 16 years experience and who earn over £20 000 per year. We would need to use all three files, which are held by three different departments.
2. Also, because data is not shared, a change in information, such as a change in surname because Jane got married, would cause three files to need updating.
3. If two people need to look at information at the same time then it is important to photocopy the information, which is time consuming and wasteful.
4. If a file is put back in the wrong place, finding it again can be a challenging task.
Computerized Databases
Advantages
The main advantages of a computerized database are as follows:
1. It is usually necessary to store the information only once, since most database softwares allow you to access information from files.
2. Files can be linked together, which means that if you update one of the files, the other files that depend on the same information will also be updated automatically.
3. If you can fine that record structure needs changing after you have put a great deal of data into a database, this is easily done. To do this manually would be impossible.
4. Access to the information is rapid and there is likelihood of the data becoming lost.
5. Validation check means there will be fewer errors in the data.
Disadvantages
The main disadvantages of a computerized database are as follows:
1. If a computer breaks down, you are not able to access the details.
2. It is easy to copy files, so sensitive data needs to be protected.
3. Training is needed to use the system and this takes time and money.
Practical
Filtering
Filtering is a quick and easy way to find and work with a subset of data in a range. A filtered range displays only the rows that meet the criteria.
*Criteria: Conditions you specify to limit which records are included in the result set of a query or filter you specify for a column.
Unlike sorting, filtering does not rearrange a range. Filtering temporarily hides rows you do not want displayed. When Excel filters rows, you can edit, format, chart and print your range subset without rearranging or moving it.
You can apply filters to only one range on a worksheet at a time.
To filter,
Click on a cell in the range you want to filter, and then under “Data” in the menu bar, select filter, then Auto-Filter.
Filter for the smallest number
Click the arrow in the column that contains the numbers, and click (Top 10...). In the box on the left, click Top, or Bottom. In the box in the middle, enter a number. In the box on the right, click Items.
Filter a range for rows that contain specific text
Click the arrow in the column that contains the numbers, then click (Custom). In the box on the left, click equals, or does not equal, contains, or does not contain. In the box on the right, enter the text you want.
If you need to find text values that share some characters but not others, use a wildcard character.
The following wildcard characters can be used as comparison criteria:
Use to find
“?” to find any single character. Example, sm?th finds “Smyth” and “Smith”
“*” to find any number of characters. Example, *east finds “Northeast” and “Southeast”
To add another criteria, click And or Or, and repeat the previous step.
Filter for blank or nonblank cells
Click the arrow in the column that contains the numbers, then click (Blanks) or (NonBlanks). Note: The Blanks and NonBlanks options are available only if the column you want to filter contains blank cells.
Filter for numbers greater than or less than another number
Click the arrow in the column that contains the numbers, and click (Custom).
In the top box on the left, click “is greater than”, “is less than”, or “equal to”. In the box on the right, enter a number.
To add another criteria, click And or Or, and repeat the previous step.
Filter for a number equal or not equal to another number
Click the arrow in the column that contains the numbers, and click (Custom).
In the top box on the left, click “equals or “does not equal”. In the box on the right, enter a number.
To add another criteria, click And or Or, and repeat the previous step.
Filter for the beginning or end of a string
Click the arrow in the column that contains the numbers, then click (Custom). In the box on the left, click begins with, or does not begin with, contains, or does not end with. In the box on the right, enter the text you want.
If you need to find text values that share some characters but not others, use a wildcard character.
The following wildcard characters can be used as comparison criteria:
Use to find
“?” to find any single character. Example, sm?th finds “Smyth” and “Smith”
“*” to find any number of characters. Example, *east finds “Northeast” and “Southeast”
To add another criteria, click And or Or, and repeat the previous step.
Comments
A comment is a note that you attach to a cell, separate from all other cell contents. Comments are useful as reminders to yourself, such as noting how a complex formula works, or to provide feedback to other users.
Viewing Comments
Microsoft Excel provides several ways to view comments. Cells with comments have indicator triangles in the upper-right corners. If you rest the pointer over a cell that has an indicator, its comment appears. You can also display comments continuously- either individual comments or all the comments on the worksheet. The Reviewing toolbar steps you through each comment in a workbook in sequence. You can also print out the comments, either in place on the worksheet or as a list at the end of the printout.
User names in comments
Comments are identified by user name, so that you can tell who entered each comment in a shared workbook or a workbook being routed to several users for review. When you merge changes from several workbooks, the comments are also combined so all comment text for a cell appears in sequence. They also make data entry easier and the program more user-friendly.
STEPS
1. Select the cell for the header
2. Select INSERT from the menu bar
3. Select COMMENT
4. Type your comment
Range Name
Naming a range in a worksheet enables one to represent a set of numeric data in a specified range with one variable. This variable can be used to perform any related data analysis.
STEPS
1. Highlight the range
2. Select INSERT from the menu bar
3. Select NAME
4. Select DEFINE
5. Type the name
Charts
A chart or graph is a type of information in graphic or a graphic organizer that represents tabular numeric data and/or functions. Charts are often used to make it easier to understand large quantities of data and the relationship between different parts of the data. Charts can usually be read more quickly than the raw data that they come from. They are used in a wide variety of fields, and can be created by hand (often on graph paper) or by a computer using a charting application
Certain types of charts are more useful for presenting a given data set than others. For example, data that presents percentages in different groups (such as “satisfied, not satisfied, and unsure”) are often displayed in a pie chart, but are more easily understood when presented in a horizontal bar chart. On the other hand, data that represents numbers that change over a period of time (such as “annual revenue 1990 to 2000”) might be best shown as a line chart.
Types of charts
1. A scatterplot uses Cartesian coordinates to show the relation of two or more quantative variables
2. A histogram typically shows the quantity of points that fall within carious numeric ranges (or bins)
3. A bar graph uses bars to show frequencies or values for different categories
4. A pie chart shows percentage values as a slice of pie
5. A line chart is a two-dimensional scatterplot of ordered observations.
Validation
LIST validation is used when a set of data repeats itself. It is used to make data entry faster and also reduces the chance of making mistakes
Validation using list
1. Highlight the range
2. Select DATA from the menu
3. Select validation
4. Select LIST from settings
5. In the source textbox, type the data separated by commas
Validation using whole number
This is used when entering whole numbers within a range
1. Highlight the range
2. Select DATA from the menu bar
3. Select validation
4. Select WHOLE NUMBER from settings
5. Enter minimum and maximum values
6. Enter input and error messages
