Chapter 1.11 Characteristics of Information Systems

Chapter 1.11 Characteristics of Information Systems

1.11 (a)      Passive and Interactive Information Systems

An information system is a system that provides information according to a user’s requests.

Passive information systems.

Passive information systems are systems that will answer queries based on the data that is held within them, but the data is not altered. A simple example would be an electronic encyclopaedia where queries can be used to search for data and much valuable information can be learned, but the user is not allowed to alter the data. Another example would be the student file in a school that can be accessed by members of the teaching staff to find out where a student is at a particular time of day, or to look up their telephone number in order to contact the parents. The database of information is a valuable resource but it is not possible for an ordinary teacher to alter it.

Interactive information systems.

An interactive system is one in which data can be entered for processing, which may alter the contents of the database. An example would be the school secretary updating the attendance record of a pupil in the pupil file. In commerce, a stock control system in a supermarket is an interactive information system because it not only gives information like the price and the description of the goods for the till receipt (passive), but also updates the number in stock immediately (interactive) so that when the next item is sold the number in stock has already been altered.

1.11 (b)      Management Information Systems

A management information system is software that allows the managers within a company to access and analyse data.

The management within a company, or any other organisation, is usually working on two levels. These levels may be different levels of management or may be the same people but with two different tasks. One is the day to day management of the organisation, keeping track of invoices, ensuring that the business has enough stock, arranging for the workers to be paid… The other is the strategic management, making decisions about what items of stock to keep, what new items to stock, what to discontinue…

The first of these management tasks is condition driven. The information system can be used to trigger decisions that have to be made. A certain item is reported to be low in stock by the system, requiring a decision to be made as to whether to reorder and how many to reorder.

The second of these management tasks is to look at the wider picture. To extract information from the system which can inform wider decisions like should an item be stocked, which areas of the business are doing well and which are not, which workers are having to do a lot of overtime which may point to the need to increase staff in that sector.

Such reports are termed Strategic level reports because they inform the executives who need to decide the strategy that the company is to follow.

1.11 (c)      Applications requiring Batch Processing/Rapid Response

Batch processing.

A batch processing system is used when the output does not have to be produced immediately. Other factors are that the application will tend to use a large amount of data, that processing will tend to be of the same type for each set of data and that human intervention is not necessary. In section 2 we saw that the perfect example of batch processing is the payroll system, and nothing has changed because we are in a different section.

Rapid response processing.

Real time processing can be thought of as being used in process control where the results of the process are used to inform the next input. A good example would be the control of a robotic machine on the production line. The other example is in information systems where it becomes necessary to update the file of information before the next enquiry is dealt with. The classic example is the airline (or theatre) booking system. If a customer enquires whether there is a seat available on the flight, and in response to a positive reply decides to buy the ticket, then the number of tickets now available must be updated before the next person makes an enquiry, otherwise the second person may be sold the same seat. Similarly, the mail order company will need to change the number of items in stock before the next query arrives.

1.11 (d)       Expert Systems

An expert system is one which contains as much data as possible about a restricted knowledge area. The data is collected from as many expert sources as possible and stored in the system, in this way it is hoped that the system contains all the knowledge about that topic that there is. 

For this reason, these systems are sometimes called knowledge systems. The use of expert systems relies on the belief that for any given area of knowledge there are rules that always apply to that knowledge and that they can be applied according to a logical ordering. This can apply to scientific principles well, for example if there is a rule that oil is always found between two particular types of rock strata, then if the system identifies the strata it can determine, according to the rules, where to drill for oil. Because it follows scientific principles, oil exploration is a good example of the use of expert systems. It is particularly useful because the data that is collected is logged on computer systems when it is collected so it seems sensible to use this information as input to the expert system because it is already in computer readable form.

Expert systems need four parts in order to produce sensible results:

·        A lot of data. This is all the data that the system has been told about the application area. It is called the knowledge base. Imagine a medical expert system. The knowledge base would be created by collecting all the knowledge about diseases from all the best doctors in their fields.

·        A set of rules that apply to the situation. “If the patient has a headache then they should take two aspirin”. This is called the rule base.

·        It is no good having a set of rules and a big collection of knowledge if there is nothing that can apply the rules to the knowledge to come up with sensible solutions. The thing that does this called the inference engine. This is what decides whether the patient should be given aspirin. Some people are not allowed aspirin, certainly not if the patient has an ulcer or…, it is the inference engine that checks through everything to find out what will fit all the rules.

·        After a decision has been made, the system must be able to tell the person what the result is. The fourth part of the system, therefore, has to be an HCI.

Example Questions

1.      Explain the difference between a passive information system and an interactive information system, giving an example of each.                                                (4)

2.      A company payroll system uses a personnel file among others.

   a)   Explain the difference between batch processing and rapid response processing. (2)

   b)   Explain how batch processing  and rapid response processing can both be sensibly used in the context of the personnel file being used to calculate the payroll.         (4)

Read More

Chapter 1.10 Designing the User Interface

Chapter 1.10 Designing the User Interface

1.10 (a)      Importance of Good Interface Design

However complex the software, however expensive and powerful the hardware, the system is unusable if there is no intuitively simple to use interface with the human being who is in control of the system or for whom the system is producing results. 

The HCI must be unambiguous, allow the user to input all the data that the user thinks important, and produce the output in an easily understandable form.

The intended user of the interface must be taken into account. The interface design for a pre school playgroup to learn about numbers is going to be very different from the design of an interface for the manager of a chemical plant to keep a check on the reactions around the plant. The interface that this manager would use to study a particular reaction (perhaps tables of figures, or graphs showing the different parameters of the reaction) is very different from the interface the same person would use if they were wanting to see the flow of a chemical around the whole site. This would probably be in the form of a diagrammatic representation of the site. The circumstances under which the interface is to operate are also important. In the last chapter mention was made of the nurse looking after a group of patients. In those circumstances an audible warning that a problem may be occurring is far more sensible than a visual one which may be ignored if the nurse’s attention is drawn away from the screen. Finally, the designer of the interface needs to take account of the purpose for which the interface was designed, namely the transfer of data into the system and the communication of information from the system to the user. If the user is using the computer to play a game then the paramount importance of the interface is that it adds to the enjoyment of the user.

Consideration of the purpose of the interface,

·        who it is for

·        what information needs to be conveyed

·        the circumstances under which the interface must operate

·        the effectiveness of the communication

·        the enjoyment obtained from using it

are all important when the interface is being designed.

1.10 (b)      Peripheral Hardware for a Given Application

This section deals with the needs of the application rather than the peripheral devices themselves. For details of the devices the reader’s attention is drawn to chapter 1.5.

When peripheral devices are chosen a number of factors need to be taken into account.

·        Who are the people that are going to use the application? Specifically, consideration must be given to their age (can they read is an obvious question), their ability with computer systems, their understanding of the software in use (do they need to be given instruction about how to use it or do they know what is expected of them?), any physical disabilities which may make some hardware impossible to use.

·        Is the system automated in any way? If so the peripherals may include sensors and actuators.

·        Under what circumstances will the system be used? If the input and output devices are to be used in the open air then the environment will dictate some restrictions which would not be necessary if the system was being used in a computer room.

·        The software that is being used. The software will dictate the type of input required and the type of output that will be produced, consequently it will also have an influence on the peripherals that are suitable for that input and output.

1.10 (c)      HCI Design Issues

Short term and Long term memory

The information produced by a system can be of such a large volume that it is not possible for all the information to be stored for future use by the user. Some of the information is presented via the user computer interface, perhaps in the form of a scrolling graph. Such data is very transitory in nature because the screen display is being constantly updated. Such data is part of the short term memory. The long term memory is that which stores the data for future reference.

Visual perception

This includes all the information that is presented by the system in such a way that it can be seen with the eyes. This means that the information will be presented on a screen or on a hardcopy produced by a printer. The size of individual pieces of information will be important as will the contrast used and the type of font in the case of text.

Colour

Colour is an important part of any HCI. The contrasting use of colours can highlight the more important information, or can be used to distinguish one type of information from another. The different levels of contrast between colours are necessary if the individual items of information are to stand out. Black on white provides the highest possible contrast, while dark blue on black is very difficult to decipher.

Layout

The layout of the data on the screen is important. The eye naturally reads from left to right and from top to bottom. This means that more important information should be positioned toward the top and left of the screen. The volume of information on the screen at any one time is also important because there is a limit to the amount that the eye can follow and the brain distinguish in one sweep of the screen content. If the information should be seen in an order, then the correct screen order is from top left to bottom right corners, as the eye naturally reads.

Content

The content of the information presented is important because a user will soon begin to ignore items of information that are constantly being put on the screen despite not being necessary. Similarly, if a method is used to show that a piece of information needs urgent attention, while the operator does not perceive the urgency, then all such highlighted information may be begun to be ignored in the same way.

1.10 (f)       Speed Mismatch

A typical computer system will consist of the processor to do the necessary calculations or other processing, the peripheral devices to allow input, output and storage of data/information, and the human being that is using the computer. 

The processor can carry out its side of the task at great speed while the human being is very slow, both at providing input and making sense of the output. This difference in speed is known as the speed mismatch between the operator and the processor. Peripheral devices work at far greater speeds than the human being, but are considerably slower than the processor, consequently there are also speed mismatches on both types of communication concerning peripherals. If there are enough computer systems this speed mismatch does not matter so much, but if there is a shortage of processing time, then a method needs to be found to keep the slowest parts of the systems isolated from the processor. One way of doing this is to use batch processing (see section 2).

The speed mismatch causes more problems if the decisions of the computer need to be  acted upon immediately. If a computer is being used to control the insertion of the graphite rods into a nuclear reactor it may become important to ignore the human being once the decision has been made and simply to report that an action has been taken after the event. In this way the speed mismatch has been overcome by cutting out the slowest part of the system.

Example Questions

         A company has a workforce of around 2000. Some work in the office using the computer system for administrative tasks, while others use the computer system on the production line for giving details of orders that need to be manufactured.

1.      Describe the factors that would have been important in the design of the software interfaces to be used by the office workers and the shop floor workers.        (6)

2.      Select appropriate peripheral hardware for these two application areas, giving reasons for your choices.                                                       (12)

3.      The office workers often have to key in the details of new members of the workforce. The details of the worker are on a standard form which the new employee fills in. Explain how a form based software interface would be useful to the worker who has to key in the data.                                                           (4)

4.      Explain the types of output that would be expected from the computer on the factory production line, if it is used to control the speed of the production line as well as being used as a tool for the workers.                                         (4)

5.      Explain why speed mismatch would mean that the computer should be in control of the speed of the production line.                                                   (3)

Read More

Chapter 1.9 Handling of Data in Information Systems

Chapter 1.9 Handling of Data in Information Systems

1.9 (a)        Manual and Automatic methods of Data Entry

All computer systems need to have data input to them otherwise they have nothing to process. The methods of collecting the data can be divided into two types: automatic and manual data collection.

Automatic Data Collection

The input devices used here are:

OMR: for multiple choice answer sheet marking

OCR: for scanning of documents that can be modified

MICR: for clearing bank cheques

Sensors: Here data will be captured in analogue form. Hence, there is a need for an Analogue-to Digital Converter to convert the data in digital form before sending to the computer.

1.9 (b)        Methods of Image Capture

Scanner:

Used to convert printed text or graphics into digital form.

Video capture card

A video picture is made up of a series of images which are changed approximately 26 times per second in order to fool the brain into thinking that the images are moving. A video capture card is an interface board which fits into one of the expansion slots in a processor that allows the processor to store the values of the screen pixels for a specific picture. In other words it allows the action to be frozen. A typical example of the use of a video capture card is the market stall that uses a video camera to take an image of a customer and then to select one image to print onto a T shirt.

Digital camera

Works in a similar way to an optical camera but does not store the image on film. Instead, the image is stored electronically enabling the user to download it into a computer and manipulate the image and print out the images if desired.

Each of these image capture systems results in an electronic image being stored in the computer system. Image manipulation software can then be used to alter or edit the image in any way that is required. While this allows the user to use their imagination and to tidy up pictures or crop them to miss out unwanted parts of the image, it also allows unscrupulous people to produce pictures with very little foundation in reality. It used to be said that: “The camera never lies”, this is certainly no longer true, witness the film Forrest Gump.

1.9 (c)        Validation and Verification

Verification

Verification means checking the input data with the original data to make sure that there have been no transcription errors. The standard way to do this is to input the data twice to the computer system. The computer then checks the two sets of data (which should be the same) and if there is a difference between the two sets of data the computer knows that one of the inputs is wrong. It won’t know which on is wrong but it can now ask the operator to check that particular input.

Validation

The first thing is to dispel a common misinterpretation of validation. In section 1.6.f checking of data was mentioned. Specifically, the use of parity bits to check data. This is NOT validation. Parity bits and echoing back are techniques that are used to check that data has been transmitted properly within a computer system (e.g. from the disk drive to the processor), validation checks are used to check the input of data to the system in the first place.

Validation is a check on DATA INPUT to the system by comparing the data input with a set of rules that the computer has been told the data must follow. If the data does not match up with the rules then there must be an error. There are many different types of validation check that can be used to check input in different applications.

1. Range check. A mathematics exam is out of 100. A simple validation rule that the computer can apply to any data that is input is that the mark must be between 0 and 100 inclusive. Consequently, a mark of 101 would be rejected by this check as being outside the acceptable range.

2. Character check. A person’s name will consist of letters of the alphabet and sometimes a hyphen or apostrophe. This rule can be applied to input of a person’s name so that dav2d will immediately be rejected as unacceptable.

3. Format check. A particular application is set up to accept a national insurance number. Each person has a unique national insurance number, but they all have the same format of characters, 2 letters followed by 6 digits followed by a single letter. If the computer knows this rule then it knows what the format of a NI number is and would reject ABC12345Z because it is in the wrong format, it breaks the rule.

4. Length check. A NI number has 9 characters, if more or fewer than 9 characters are keyed in then the data cannot be accurate.

5. Existence check. A bar code is read at a supermarket check out till. The code is sent to the main computer which will search for that code on the stock file. As the stock file contains details of all items held in stock, if it is not there then the item cannot exist, which it obviously does, therefore the code must have been wrongly read.

6. Check digit. When the code is read on the item at the supermarket, it consists of numbers. One number is special, it is called the check digit. If the other numbers have some arithmetic done to them using a simple algorithm the answer should be this special digit. When the code is read at the check out till, if the arithmetic does not give the check digit it must have been read wrongly, it is at this point that the beeping sound would normally be heard if everything is alright.

1.9 (d)        Output Formats

When data has been processed by a computer system it is necessary to report the results of the processing. There are a number of different ways that the results can be reported to the user.

Graphs

Graphs show trends very clearly.

Reports

A report is a hard copy printout of the values of variables. This has the advantage of producing the actual figures according to the values specified by the user. However, the figures themselves may need skill to interpret their significance and the value of figures in a vacuum is often hard to justify.

Interactive presentations

The previous forms have relied on the format of the report being decided without the luxury of being able to see what the figures look like in the first place. If the system allows the user to decide the type and range of output required during the run then there is some positive user involvement leading to an interactive presentation where the user can adjust the output to suit their needs.

Sound

Many applications do not lend themselves to a standard, visual, printout. Sound can be used for output from some systems. Obvious examples would be voice synthesis for reporting to blind people and an alarm system to protect property against burglars.

Video

Video is a visually satisfying form of output that takes large amounts of memory to produce because the nature of the medium requires large quantities of pictures to produce the feel of continuous motion. Video is useful for demonstration of techniques where there is little value in pages of instruction if a simple video can illustrate something better.

Images

‘Images’ can refer to any of the forms of output mentioned when they are shown on a monitor screen, as opposed to the hard copy produced from a printer.

Animations

Provide a good stimulus for an audience and lead from one slide to another when making a slide based presentation. Animation takes considerably less processing power than other forms of motion, unless the image being animated is complex. Animation is used so often that it can come across as being a boring technique that has just been added for ‘gloss’.

Example Questions

1. a)  State two methods of data entry used by banks in their cheque system.          (2)

    b)  Explain why banks find the use of your two examples suitable for this application.   

2.      A small stall is to be opened, as part of a fairground, where the customer can have their likeness printed on to the front of a sweatshirt. Describe two possible methods of capturing the image to be printed.                                                (4)

3.      A mail order firm receives orders from customers on paper order forms. These are keyed into the computer system by operators. The data that is to be keyed in includes the 5 digit article number, the name of the customer and the date that the order has been received.

   a)   Explain how the data input would be verified.                                     (3)

   b)   Describe three different validation routines that could be performed on the data. (6)

4.      A reaction vessel in a chemical plant is monitored, along with many others, by a computer system using a number of sensors of different types. Describe three different types of output that would be used by such a system, stating why such a use would be necessary. (6)                                                                             

5.      Explain what is meant by the timeliness and relevance of data.           (2)

Read More

Chapter 1.8 Choosing Applications Software

Chapter 1.8 Choosing Applications Software

1.8 (a)        Custom Written and Off-the-Shelf Software.

When the analyst has analyzed the problem and come to a conclusion about how it can be solved, a decision has to be made about the software that should be used.

There are many pieces of software that have already been written and are immediately available to buy. This type of software is called ‘off-the-shelf’ software because you can literally go into a computer shop and pick a copy off the shelf. There are a number of advantages in buying an off-the-shelf package:

·        The software has already been written and so is immediately available rather than having to wait, sometimes a considerable time, for it to be written.

·        The software will be used by many people or organisations, therefore they share the development costs rather than one having to foot the whole bill. This implies that the software will be considerably cheaper.

·        Copies of the software have been in use for some time and will have been in use by a variety of users. This means that any bugs in the software should have been found and rectified, consequently it can be expected to work.

·        If it comes as part of a suite of software it can be relied upon to be compatible with other applications, allowing, for example, the import of data.

·        Because the software will be in general use there are likely to be well established training courses for the staff to be sent on to learn about the software.

A Custom package is one that has been specially written to solve a specific problem. Perhaps there is no freely available piece of software that will satisfy the needs of the company, A piece of custom software should mean that the organisation gets a piece of software that will do all the things that it requires doing, and, equally importantly, does not contain extra routines that will never be used.

1.8 (c)        Generic Applications Software.

Word processing.

Used for applications that have the need to communicate with others using text. Writing letters, mail merging, preparing text documents for use in other software packages, are all typical uses of a word processing package.

Spreadsheets.

 A spreadsheet is particularly useful because it can store different types of data, including numerical data, and that it can perform calculations on the areas (cells) where the numerical data is being stored.

Desktop publishing (DTP).

This type of software is characterised by the ability to produce a page of printed output that has been designed by using advanced layout techniques. The page may well contain text, graphics, tables and many other types of output each one of which may be better produced using a word processor or a drawing package or a spreadsheet. The value of the DTP is that it contains powerful tools for arranging these individual items on the page, the printout of which can be used directly as the starting point for a printing process. Typically DTP software is used for the production of leaflets, posters, proof copies of books and magazines.

Presentation software.

. The software allows for the preparation of a show which typically follows a storyboard of individual screens. The software allows morphing from one screen to another and also allows animation and full use of text and graphics within individual screens. If required, a soundtrack can be added to complement the pictures being shown.

Drawing packages.

This is a package that produces graphics output. Often such output is exported to a DTP for inclusion in some publication, or to a piece of presentation software for inclusion in a display sequence. Another use for such output is to enliven a page on the world wide web. There are many different forms of graphics package split into groups dependent on the way that the graphic is produced. The two most common are bitmap graphics where each pixel is treated separately, and vector graphics where the lines on the drawing are created mathematically. Different software packages create the graphics in different ways for instance Paintbrush creates pictures in bitmap form while Draw uses vectors. The simple way of describing the difference is in sizing the drawing. If a drawing held as a bitmap is increased in size then each of the pixels is increased in size and hence becomes more obvious. If a drawing stored using vector graphics is increased in size the only thing that changes is the mathematical formulae for producing the lines, which will produce a picture of comparable quality whatever the size.

1.8 (d)  Applications for which Common Packages are not appropriate

Common applications packages are those that have been designed to satisfy particular needs that are common to a number of different applications. There are many other examples where computers are necessary but where the use is so specialised that the software will need to be written (or at least tailored) for that particular use. Uses that would require such specialist software are legion, but would include many uses of control software. Robots used on production lines tend to be one-off machines, designed for that particular purpose, consequently, the software that would drive them would, similarly, be one-off. A stock control system in a warehouse would have standard modules, but would have other sections which would be for that warehousing system alone. The important consideration is how different from the standard design is the system for which we want the software, the further away from the standard, the more difficult it is to use standard software, and the more likelihood there is that the system will require software written specially for it.

Example Questions.

1.      Discuss the reasons that a solicitors’ practice would have for choosing off-the –shelf software rather than custom written software if it was decided to change the word processor currently being used because it was perceived to be out of date. (4)

  

2.      In the same scenario, State two reasons why custom made software might be more appropriate than off-the-shelf software.  (2)

                                       

3.      Describe how CAD/CAM can be used to produce prototype designs in a manufacturing process.                                                                (4)

4.      A firm produces widgets for sale to the brewing industry.

         A brewing company may come to the firm with a proposal for a widget to fit a particular container which will need to be produced by the firm which will then ship the finished product in batches and invoice the brewing company. Sometimes the sales team will be sent to try to persuade the brewing firm of the advantages of the company’s widgets.

         Explain how the company can use commonly available software in the running of its business.                                                                                   (6)

Read More

Chapter 1.7 Systems Development Life Cycle

Chapter 1.7 Systems Development Life Cycle.

1.7 (a)        System Lifecycle as an Iterative Process

When considering the systems development life cycle it is important to think of the different stages as a continually developing process rather than each stage being an end in itself.

When one of the stages is completed the following stages may mean that the previous ones may need to be considered again. If the problem definition agreed with the end user later proves to be impossible to implement then the problem will have to be redefined. If the required input proves to be not feasible then it may be necessary to alter the expected output. If, during the training of the staff, one of the input operators proves to be colour blind then the input screens may need to be altered in order to not have any clashes between red and green.

This reliance of each stage being on the following stages as well as the previous ones means that the process is said to be iterative.

1.7 (b)        Problem Definition

It is important from the outset to ensure that when a computer system is being designed all those that are involved are agreed about the aims of the system.

There will normally be a person, or a company or organisation that decides that a task would benefit from computerisation. This belief normally arises because there is a problem which cannot be solved by  previously used methods or similar problems seem to have been solved by computerisation elsewhere. Unfortunately, the owner of the problem probably understands the problem itself quite well, but does not understand the consequences of using computers to try to solve the problem, or, indeed, whether such a solution is even possible. For this reason it is necessary for the organisation to employ a specialist who does understand computers and computerised solutions to problems. This is the systems analyst. Unfortunately, it is probable that the systems analyst is not expert in the area of the problem.

The system analyst’s job is to solve the problem by planning and overseeing the introduction of computer technologies. The owner of the problem will be happy if the analyst can introduce a computer solution. The problem arises when the analyst, who doesn’t know very much about the business, solves the problem that they think needs solving, while the owner of the problem expects a very different problem to be solved.

The definition of the problem is the most important part of the analysis because if it is not done correctly the wrong problem may be solved.

1.7 (c)        A Feasibility Study.

When the organisation and the systems analyst have agreed the definition of the problem, a decision must be made about the value of continuing to develop the computerised solution. The organisation may be convinced that there is a problem to be solved, and that its solution will be worth the effort and the expense. However, the systems analyst is being paid to look at the problem, and its solution, from another point of view. The analyst is an expert in computer systems and what is possible with computer systems. This analyst must consider the problem from the point of view of the computerised part of the solution and make a report to the organisation saying whether the solution is possible and sensible. This report is called the feasibility study because it says whether the solution is feasible.

The feasibility study will consider the problem, and the proposed solution, from a number of points of view.

·         Is the solution technically possible? A car firm may decide that if robots are used on the production line to assemble the different parts of engines then quality of work may improve. However, if it is not possible to manufacture a robot arm of the correct dimensions to fit into the small areas under a car bonnet, it doesn’t matter how big an improvement there would be in the quality of the finished product, it would simply not be feasible

.

·         Is the solution economic to produce? Perhaps the robots exist that can be programmed  to assemble this engine and the benefits will be worthwhile. However, if the cost of the robots and the program to control them is so great that it puts the car manufacturer out of business, the introduction of the robots is not feasible.

·         Is the solution economic to run? It has been decided that there are tremendous benefits in producing a robot production line and the robots are very cheap to buy, but they have so many electric motors, and they are so slow at assembling the engines that it is cheaper to employ people to do the job.

·         What is the effect on the human beings involved? If the car plant is the only major employer in the region, and the introduction will put much of the workforce out of work, then the employer may decide that the human cost is too great, certainly the Government would.

·         Is the workforce skilled enough? It will be necessary to employ highly skilled technicians to look after the robots. If there are no workers with the necessary skills then the computerisation is not feasible.

·         What effect will there be on the customer? If the customer is likely to be impressed with the introduction of the new systems then it may be worth the expense, however, if the customer will notice no difference, what is the point?

·         Will the introduction of the new systems be economically beneficial? Put bluntly, will the introduction of robots increase the profits made by the firm?

If the feasibility study shows a positive result which is accepted by the company, the next stage will be for the analyst to collect as much information about the process as possible.

1.7 (d)        Information Requirements of a System and Fact Finding

There are three accepted methods of finding out people’s views:

1. By interview. Interviews are particularly important because they allow the interviewee to talk at length, and also to leave a prepared script. However, they are very time consuming and consequently restricting in the number of people whose views can be sought.

2. By using questionnaires. Questionnaires make it possible to find out the views of a large number of people very quickly, but because the questions are pre-determined the person who is supplying the answers may find difficulty in putting their point of view across.

3. A compromise is to hold a group meeting. This allows a number of people to discuss points and make their views known and yet cuts down on the amount of time spent in interviews getting the same answers over and over again. The problem with meetings is that one or two people tend to dominate, not allowing all the members of the group to give their opinions.

1.7 (e)        Requirements Specifications

The planning of any system design must start by deciding what the requirements are of the system. A system may need to store data for future reference or processing. However, simply being aware that the system may need to store data is not enough.

·         Decisions need to be made about the types of data to be held as this will dictate the form that the data will be stored in and the amount of storage space required for each set of information.

·         Calculations as to the number of sets of data that are going to be held have to be made because the volume of storage will make some storage devices more sensible than others. Also, the volume of storage can affect the structures that will be used to store the data.

·         Decisions need to be made about the relative importance of the different ways of accessing the data. Is it going to be necessary to access individual items of data or will all the data be accessed at the same time?

·         Will the data be changed regularly or is it fairly static?

1.7 (f)         Data structures, Input/Output, Processing

Input Design

All systems require input. The way that the data is input to the system depends on a number of factors.

·         The data that is required. Is it graphical/textual/physical in nature? Is the data already in existence or does it need to be collected first?

·         The hardware that is available. Is the data to be entered via a keyboard by an operator, or is there an automatic way to enter the data?

·         The experience of the operator.

·         The design of the user interface.

Output Design.

The results that are produced by the system must be presented in a way that is appropriate for the application. If the system is designed to produce bank statements for customers, then it would not be sensible to have an audio output. Similarly, a burglar alarm system would not serve the purpose for which it had been designed if the output is a message on a computer screen saying that someone has broken in as there is probably no-one in the house to read it, which is why the alarm was needed in the first place.

The decision about the type of output will depend greatly upon the same factors as the input, namely, the hardware available, the form that the output needs to be in, the experience of the operator, indeed, whether there will be an operator present.

Equally important to giving enough information, is the danger of providing too much. In order for users to be able to understand the information presented various tricks can be used.

·         Information can be arranged on a monitor screen by always putting the same sort of information in the same place. The operator will then quickly become accustomed to the relative importance of different areas of the screen.

·         Information can be colour coded. Important information may appear in red while that which is less important is in black

·         Video reversal can be used to highlight a particular piece of information effectively. This is when the normal writing on the screen is black on a white background, but the piece that needs to stand out is shown as white on a black background.

·         Very important pieces of information may be shown as a dialogue box obscuring the rest of the screen until it is dealt with.

·         A printer may be reserved for special messages so that a hard copy of the information is preserved. Again, the fact that the information appears on that printer means that it has a particular importance.

·         Information can be made to flash, or can be printed in a different size, anything that makes the operator’s eye go to that part of the screen.

Jackson diagrams:

A Jackson diagram starts with the original problem as the highest level. The next, and subsequent, levels show how the problems in the previous levels are split up to form smaller, more manageable, problems. This continues until each of the blocks in the lowest levels are self contained, easily solvable problems. These individual problems can then be solved and combined according to the links that have been used. If the links between the different blocks are then used correctly, the result will be a solution to the original problem. Imagine a Jackson diagram as a method for showing the individual modules that go to make up a solution to a problem and the relationships between them.

 

An example of a Jackson diagram to show the solution to a simple problem.

A register is taken of the 25 students in a class. Each student can be either present or absent. It is necessary to print out the number of students who are present and the number absent.

 

Data flow diagrams:

These are diagrams that are used to describe systems. Boxes are used to stand for input, processes, storage, and output. Arrows show the direction of communication around the system, and communications outside the system. As the name implies, these diagrams are used to show the directions of flow of data from one part of a system to another. Data flow diagrams can have complex shapes for the boxes that are used, but the important thing is not the shapes of the boxes, rather the logical train of thought that has been used to produce the diagram. Rectangular boxes, though not always used, are perfectly acceptable for all elements in a data flow diagram. Such diagrams are intended to show how the processes and the data interrelate, not the details of any of the programming logic.

At this stage the analyst will also identify the hardware that will be necessary for the system to operate as the user requires, and the software characteristics that will need to be satisfied for the system to operate.

1.7 (g)        System Evaluation

Any system must match certain criteria if it is to be considered successful. This does not only apply to a computer system but any system. For example, a car must satisfy various criteria before being able to be called a car

·         it must move under its own power

·         it must be possible to steer it

·         it must have 3 or 4 wheels

·         it must have seats.

1.7 (h)        Documentation

The documentation of a system consists of all the text and graphics that explain how the system was produced, how it should be used, and how it can be maintained.

Documentation is created at different stages in the life of a system and for different people to use. Some of the different types of documentation are met in this section and others will be encountered later in the course. Indeed, much of the project work that is done in module 4 consists of producing the documentation for a problem solution.

Requirements specification

This is a list of the requirements of the customer for whom the system is being designed. It consists, largely, of the criteria that will be used for the evaluation of the finished system. It is usual for the system analyst and the customer to sign the list of requirements so that there is no confusion when the work is finished.

Design specification

Taking the requirements specification and working out the stages necessary to produce the required end product is known as the design specification. This will include the different stages, often shown in diagrammatic form as mentioned earlier in this chapter, and also the criteria for each stage of the solution. For example, one part of a solution may be the production of a file of data. The ways that this file of data relates to the other parts of the system, and the specification of the file (what is the key field? How many records will there be? What type of medium should it be stored on?) make up the design specification.

Program specifications

These will include detailed algorithms showing the method of solution for some of the parts of the problem. These algorithms may well be in the form of flow diagrams or pseudo code. The language to be used, the data structures necessary, and details of any library routines to be used will also be in the program specification.

Technical documentation

The technical documentation will include the program specifications, the coded program itself, details of hardware configurations. Generally, anything that will aid a technician in maintaining or updating a system. Indeed, technical documentation is otherwise known as maintenance documentation. This type of documentation is not intended to be accessible to the user of the system, who does not need any of these details to be able to use the system correctly.

User documentation

This is the documentation for the person who will actually be using the system. It contains those details that are needed to make the system operate as it should. Items normally included in the user documentation will be

·         examples of output screens

·         examples of valid input

·         methods of input of data

·         error messages and what to do when they appear

·         How to install the system onto specific hardware

Some user documentation is part of the software and can be called up onto the screen when it is needed. This type of documentation is called on-screen help.

1.7 (i)                   Testing and Implementation Planning

When the system has been completed it has to be implemented so that it is performing the tasks for which it was designed. Initially, this involves

·         ensuring that the correct hardware is available

·         arranging for staff to be trained in the use of the new system

·         inputting the data to the data files, either manually or by downloading them from the original system.

The system handover, itself can be done in a number of ways:

·         Parallel running. Until the system can be considered fault free, the old and new systems are run side by side, both doing the same processing. This allows results to be compared to ensure that there is no problem with the new system. Such a system is ‘safe’ and also allows staff training to be carried out, but it is obviously very expensive because of the need to do everything twice. Parallel running is used in situations where the data is so valuable that there must be no possibility of failure.

·         Pilot running. Key parts of the new system are run alongside the old system until it is considered that they have been fully tested. This is a compromise with the idea of parallel running, but it does not give a clear idea of the effects on the system of  the large amounts of data that are going to be encountered in the full application.

·         Big bang, or direct change. The old system is removed and the new system replaces it completely and immediately.

·         Phasing. Parts of a system are replaced while the remaining parts are covered by the old system. This allows for some testing of the new system to be done, and for staff training to take place, but also allows for a back-up position if the new version does not work as anticipated.

1.7 (j)                   System Maintenance and the Software Life Span

Adaptive Maintenance: Systems may be designed for a well defined purpose and may realise that purpose, hence they would be considered successful. However, the original reasons for a particular system to be created may change, the hardware may alter, the law governing a system may change. For many reasons the original system may no longer be satisfactory. One solution would be to produce a totally new system, another would be to adapt the present one so that it can be used in the new circumstances. This situation is reviewing the system and is the main reason for technical documentation.

Corrective Maintenance: While the system is running it will need attention because of faults being discovered, this again needs a technician with a set of maintenance documentation.

Perfective Maintenance: Computing and computer applications is a subject that changes so regularly through improvements in technology, new ideas, different legal frameworks trying to keep pace, that, in reality, a system should never be considered to be finished. Rather than being a linear process with a beginning, a middle and an end, it should be thought of as a circular process, continually returning to previous stages to fine tune them and take advantage of changing circumstances.

Read More

Chapter 1.6 Data Transmission and Networking

Chapter 1.6 Data Transmission and Networking.

1.6 (a)        Networks

A network is an interconnection of two or more computers. Generally, networks over small distances are called Local Area Networks (LAN) while those over great distances are Wide Area Networks (WAN). A Metropolitan Area Network (MAN) is one within a district or country.

Whether the network is a WAN or a LAN it will have the advantage of offering the users the chance to communicate with one another, to share information centrally, to share copies of software and to allow multiple access to files of data. In a LAN there is the added benefit of being able to share hardware such as printers and scanners.

To summarise:

·         Computers can be linked together to form networks

·         If the distances are short the network is called a LAN, if longer the network is a WAN

·         Networks allow computers to communicate

·         Networks allow the sharing of both hardware and software.

1.6 (b)        Hardware and Software

Components of a network

·         Network card. It is through this network card that the computer can communicate.

·         Cables

·         Servers

·         Network operating system.

Note: A modem is used to convert digital signal into analog at sending side and vice versa at receiving side. It is used to communicate over a WAN.

1.6 (c)        Network Topologies

There are a number of ways that the machines on a network can be connected together. The shape of the network is known as its topology. We are interested in three different network topologies.

1. Bus network

In a bus network the hardware items all use the same, central, communication line, known as a bus. The advantage is that the installation of the system is comparatively easy because there is only one communication line. However, the disadvantage is that a single break in the cable will stop all communications in the network.

2. Ring network

 

In a ring network the two ends of the bus are joined up. This creates a loop so that data can be sent in both directions along the cable. If there is a break in the cable, the network will continue to operate because the messages can go in the other direction.

3. Star network

 

In a star network the individual pieces of hardware are connected to some central point, usually the network server. This means that the failure of a single piece of hardware or the breaking of a connector can only affect that piece of hardware and none of the others. The wiring up of the network can be very complex, though.

1.6 (d)        Different Types of Data Transmission

Serial and Parallel transmission of data

In serial transmission only one bit of data can be transmitted at a time. Serial transmission has the advantages of being simple and reliable because the next bit is not transmitted until the current one has arrived at its destination. However, because only one bit can be transmitted at a time, the speed of transmission is slow.

If the devices are connected by more than one wire, then more bits can be sent at once. A sensible number of wires would be 8, because then a whole byte can be sent at once instead of having to send one bit at a time.

This type of data transfer is called PARALLEL transmission. Parallel transmission of data is obviously faster than serial because all the bits are travelling at the same time, but because of the fine tolerances in the transmission, it is less reliable as the bits can become muddled up.

Modes of Transmission.

If data is to be transmitted between devices, there are three different modes of transmission possible.

a) Simplex mode. If data can only travel in one direction then it is known as a SIMPLEX transmission. A good example of a simplex transmission of data is teletext information which is passed to a television receiver, but there is no way to send data in the other direction.

 

b) Duplex mode. When data can pass in both directions at the same time it is known as DUPLEX transmission of data. An example of duplex transmission would be a telephone conversation as both users can speak and be heard at the same time.

 

c) Half duplex mode. When data can pass in both directions, but only in one direction at a time, the transmission is called HALF DUPLEX. An example of half duplex is a CB radio system in which each handset can either be set to receive mode or send mode.

 

 

1.6 (e)        Bit Rates

Information needs to be sent to devices in a computer system from other devices. For example, a picture stored in the memory of the computer needs to be sent down a telephone line to another computer. Remember that the more pixels that there are and the more colours that can be represented, the better the picture will be. However there is a limit to the amount of information that can be transmitted in a given time down the phone line, so a decision needs to be made. One choice is to have as much detail as possible and accept that it will take a long time to transmit it. The other is to limit the resolution of the picture, meaning that there is less information to send so that the message will be sent more quickly.

The number of bits that can be sent in one second is known as the BIT RATE. The units used to measure the bit rate are BAUD. 1 baud = 1 bit per second.

Note that text can be sent much more quickly than other forms of information because it needs far fewer bits (1 byte per character) than other types of data. When data other than text is being transmitted, e.g. on the internet, it is important to limit the amount of data that needs to be sent or the time it takes to download the data can be unreasonably long. The data can be limited by such simple things as reducing the size of pictures so that they only take up a small part of the screen, or that they are restricted to a few colours. Speeding up the transmission of the information by reducing the amount of data that is sent is known as compression

1.6 (f)         Error checking and correcting

a) Echoing Back. The simplest way of checking the transfer of the data is to send it back again. If the data that is sent back is the same as the data that was sent in the first place then the original data must have reached its destination correctly, if not then it needs to be sent again. This is known as ECHOING BACK. Echoing back is very effective, but suffers from having to send data twice, thus taking longer than necessary, and needing to be a duplex, or half duplex, system to allow data transfer in both directions.

b) Parity. All data is transmitted as bits (0s and 1s). The Number of 1s in a byte must always be either an odd number or an even number. If two devices that are communicating data decide that there will always be an odd number of 1s, then if a byte is received that has an even number of 1s, an error must have occurred. E.g. the byte 01011000 has 3 ones in it. 3 is an odd number, so it fits the rule that it must have an odd number of ones. When it is sent there is an error in transmission so that the first bit is received as a one. So, the byte received is 11011000. This has 4 ones in it, which is an even number, so there must be an error. The receiving device would ask for it to be sent again.

Note:

·         If two mistakes are made in the same byte they will cancel each other out and the faulty data will be accepted. This problem can be overcome, and in the same way, a clever way of correcting error mistakes can be implemented. This method is not part of this course.

c) Check Sum. Data will normally be sent from one place to another as a block of bytes rather than as individual bytes. The computer can add numbers together without any trouble, so another checking procedure is to add all the bytes together that are being sent in the block of data. The carry, out of the byte, is not taken into account, so the answer is an 8 bit number, just like the bytes. This answer is calculated before the data is sent, and then calculated again when it is received, and if there are no errors in the transmission, the two answers will match.

1.6 (g)        Switching

When a message is being sent from one machine to another, particularly over a wide area network, the message may have to pass through other machines first. This may be forced on the system because there is no direct route from one machine to another.

 

In the network shown, it would be easy to send a message from A to D or from A to B because A is directly connected to both of them. However, sending a message from A to C is much more difficult because there is no direct route. There are two ways that the message can be sent

a) Packet switching. The message is split into a number of equal sized packets. Each packet has a label saying where it is meant to be going and what number packet it is. These packets are sent along communication lines towards the destination. Each time a packet reaches a node on the network the node decides which direction to send it on. So, one packet in the message from A reaches node D. The obvious route to take is the one directly to C, but it is already in use for another message, so D decides to send it to E instead. The next packet arrives at D and, this time, the line to C is free, so the packet is sent direct to C. When the message has all arrived at C it has to be reassembled in the correct order.

b) Circuit switching. Before the message is sent, the network reserves a route from A to C. The message can then be sent directly from A to C and will not need to be reordered when it gets there.

Packet switching allows optimum use of the connections around the network because as many routes are in use at one time as possible, whereas circuit switching means that the whole message is kept together so it does not need to be reassembled at the destination.

1.6 (h) and (i)      Protocols

When data is being transferred from one place to another in a computer system there must be rules set up as to how the transfer is going to be done. Typical rules would be

·         A rule about the wire connecting the two parts of the system. Errors would occur if one device had a serial connection and the other was expecting a parallel connection

·         If one device sent data at a particular bit rate and the other device read what it received at a different rate, the message would never be received correctly.

·         If one device used even parity and the other device used odd then no correctly sent byte of information would ever be accepted.

The set of rules that needs to be set up to allow the transfer of data to be carried out is known as a protocol.

1.6 (j)      Advantages and Disadvantages of Networking

Advantages.

·         The main advantage of linking computers in a network is that they can share data. If two computers each have their own copy of a database then, unless no changes can be made to it, one computer will always have a more up to date version than the other because a change made on one machine will not register on the copy of the database on the other machine. If the two machines are networked there only needs to be one copy of the database, therefore any change made to the database will be used by both machines.

·         The machines can be used to communicate, a good example being the use of e-mail over the internet.

·         On a LAN the sharing of hardware and software between machines can reduce the cost of a large amount of computer equipment being needed in a small area, although, the saving on software is not necessarily what might be thought because the license for network software is far more than for a single machine.

·         Also on a LAN, access to files does not depend upon the physical location of the user, but on who the user is. For example, in a school classroom, if a pupil was working at a particular machine at the end of one lesson they do not have to use the same machine the next lesson, they may even be in another room.

Disadvantages.

·         The fact that the network allows access to user files from more than one machine means that keeping files secure is far more difficult. Methods like user ID and password systems have to be employed to ensure that the correct users are given access to the correct files.

·         If there is a fault on the network it can affect more than one station, and if the server is faulty the whole network will fail.

Example Questions

1.      Explain the difference between a wide area network (WAN) and a local area network (LAN).                                                                                    (2)

2.      a) State three pieces of hardware that are needed to create a LAN from a set of stand alone computers.                                                                      (3)

         b) Explain why the communication over a WAN differs from that across a LAN and state how the hardware necessary for communication would differ from that used in part (a).                                                                                        (3)

3.      By drawing a diagram, or otherwise, describe a ring network and state an advantage that a ring network has over a bus network.                                            (3)

4.      Explain the difference between

         (i) simplex

         (ii) half duplex

         (iii) duplex

         transmission of data, giving an example of the use of each.                 (6)

5.      Explain why the bit rate is more important when sending a colour picture from one device to another, than it is when sending a page of text.                 (3)

6.      The following bytes of data are received by one device after being transmitted from another.

                                    01001101

                                    10001000

                                    10101011

                                    00011011

         An automatic checking technique is used to check that the data has been transmitted without error.

    a)  State which byte has been received incorrectly, explaining how you arrived at your answer.                                                                                         (3)

    b)  Explain why it is possible that a byte of data could still be incorrect despite passing the test that you used in part (a).                                                   (1)

Read More