Information Systems Development

I shall be giving 12 lectures on the ISD class COM3403 in the first semester of the academic year 2004-5.

Contents

• A list of books that are relevant to the course
• Links to the assignments
• Lecture list
• Self-assessment questions
• Sample examination questions

Some useful books

Titles in bold are particularly recommended.

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Assignments

Individual assignment

Available from week 4, submit in week 8, marked scripts returned in week 10.

The individual assignment is now available.

There is a file of questions and answers about the individual assignment.

As students work the individual assignment, they discover errors in the base documents E02 and E03, and send me change requests to correct them. I publish the change requests in the Change Request document. In writing your answers to the individual assignmemnt, you may assume that change requests 3 and 4 have been approved, and the stated changes made to the documents. The list of approved changes might increase as more errors are dicovered, so keep an eye on this page, and on the Change Request document.

Group assignment

Available from week 10, submit in week 13 (University week 17), marked scripts returned in week 16 (University week 20).

The group assignment is now available.

Please look at the list of groups to find out which group you are in. If you think you are not in any group, please email me for instructions.

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Lectures

The following table lists the lectures. The column headed Lecture gives links to ppt files that contain the lecture material. The column headed Reading gives references to text and sources of information on the World Wide Web. The column headed Glossary lists technical terms appropriate to the lecture. Some of the terms will be used in the lecture, but probably not all of them. You might need to consult the texts and other sources of information to find out about them.

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Self-assessment questions

The self-assessment questions are oganised by subject as follows:

• Analysis document
• Specification document
• Design document
• Context diagrams
• Problems and subproblems
• Problem classes and frames
• Risk management
• Quality management
• Quality achievement and control

Analysis document

1. Study the statechart for the supermarket checkout in the analysis document, and describe its operation in words.
2. In the API for a Supermarket Controller, a new checkout function is to be supported. A new key marked "Recall" is provided, and pressing this key causes details of the most recently scanned item to be displayed on the checkout screen. List the changes to be made to the analysis document to support this new function. Use the format of change request 0 in the Change requests document and create a change request for this change.
3. Look at change request number 1, and complete the section Documents affected.
4. A new operation, to be called LineList, is needed for the warehouse manager. It will display on a printer in the warehouse a complete list of all lines in the store, showing for each line the line number, the description, the price, and the current stock level. Specify the changes that must be made to the analysis document to support this new function.
5. To be continued.

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Specification document

1. Specify the changes that must be made to the specification document to support the LineList operation described in the Analysis document section.
2. Suggest places in the specification document where mathematical notation could be used to shorten the text and to make it more precise.
3. To be continued.

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Design document

1. Specify the changes that must be made to the design document to support the LineList operation described in the Analysis document section.
2. Devise a small configuration of Java objects that satisfy the design constraints, and decribe the speficiation state that they represent.
3. To be continued.

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Context diagrams

1. A computer is required to gather data from weather stations and record it in a database. The data gathered includes barometric pressure, wind speed, wind direction, air temperature, and humidity. Weather researchers can use the database for research. Data in the database can be displayed on a screen. Identify some domains in this problem and describe their shared phenomena.
2. A word processing machine is required to allow users to create and edit texts, and to print them on an attached printer. The texts will be stored in the machine. Identify some domains in this problem and describe their shared phenomena.
3. An estate agent keeps details of properties for sale in surrounding towns and villages, and details of clients, both buyers and sellers. Clients are allowed to conduct anonymous searches of the properties. The estate agent's staff can record details of new clients and properties, organise and record visits to properties, record offers made, accepted, and rejected, and record sales completed and commission earned. Each month a management report containing business statistics is produced. Identify some domains in this problem and describe their shared phenomena.
4. To be continued.

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Problems and subproblems

1. Explain the difference between optative and indicative domain descriptions. How does it happen that a single description is read as optative by one reader and indicative by another.
2. To be continued.

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Problem classes and frames

1. List Jackson's five basic problem frames, and describe briefly the characteristics of each frame.
2. Explain the difference between a causal domain and a biddable domain. Illustrate your answer with an example of a commanded behaviour problem.
3. Classify each of the following domains as biddable, causal, or lexical:
   1. The operators of a radiotherapy machine
   2. A database of properties for sale in an estate agency
   3. A bank customer using a cash issuing terminal
   4. A cash issuing terminal
   5. A transmission network linking a cash issuing terminal to a bank's central computer
   6. The bank's central computer
   7. The bank's database of customers' accounts
   8. A scanner attached to a computer
   9. A printer attached to a computer
4. The figure shows an analysis of a problem to copy images by scanning and printing under the control of a computer.
   
   1. For each domain in the diagram, classify it as biddable, causal, or lexical.
   2. Choose a problem frame that fits this problem.
   3. Add a requirement to the diagram, indicating briefly the nature of the requirement. Take care to show any constraining requirement references.
5. To be continued.

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Risk management

1. Create a risk register for a one-person project whose cardinal aim is to pass the ISD examination with a mark of at least 70%. Draw the cause-effect tree, and identify any risk reduction measures, classifying each as pre-emptive or reactive.
2. Read the description of the formal methods project, identify some risks, and suggest how they might be reduced or avoided.
3. Read the description of the system integration project, identify some risks, and suggest how they might be reduced or avoided.
4. Read the description of the estate agents' back end project, identify some risks, and suggest how they might be reduced or avoided. The use of a VDM specification is itself a risk reduction measure. What risks is this specification trying to reduce?

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Process models

1. Devise a process model for passing the ISD examination with a mark of at least 70%.
2. A certain process model includes a program design activity followed by a program coding activity. When the program coding activity is completed a review is held with the following objectives:
   • To determine whether the program code is a correct representation of the design
   • To determine whether the program text meets the organisation's coding standards.
   Suggest some risks that are being addressed by having these stages in this order in the process. Also suggest how each of the objectives of the review contributes to product quality.
3. Use the World Wide Web to find out about the Dynamic Systems Development Method (DSDM).
4. Use the World Wide Web to find out about the Cleanroom development method.
5. To be continued.

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Quality management

1. For each of the following quality attributes, classify it as functional or non-functional:
   • When a withdrawal is made from the account, the account balance is decreased by the amount of the withdrawal.
   • User manuals are to be written in English and in the present tense.
   • In the first year of operation, users must not discover more than one error per thousand lines of code.
   • The error messages are to be in English.
   • Every transaction is to be logged.
   • When the account statuses are displayed, accounts with debit balances are to be shown in red, while accounts with zero or credit balances are to be shown in black.
   • The colour scheme for the operator input windows should be such as to allow users with red/green colour blindness to operate them effectively.
   • As each transaction enters the system it is to be given a reference number from 1 upwards.
   • There must never be two transactions in the system with the same reference number.
   • If contact is lost with a remote database for a period exceeding 10 seconds, the local transaction must be terminated and its effect backed out.
2. Explain, with examples, the difference between developer-driven quality attributes and user-driven quality attributes.
3. Why is it important for quality attributes to be measurable? Why is it that in general functional attributes are easier to measure than non-functional attributes?
4. The following usability attribute was proposed for a word processor:

   "When a piece of text has been selected on the screen, the user can correctly predict the effect on the document of pressing the delete key."

   Comment on the completeness and measurability of this attribute.

   For a named word processor with which you are familiar, suggest some functional quality attributes that are related to this usability attribute.

5. To be continued.

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Quality achievement and control

1. Explain the meanings of the terms process, method, and notation as applied to software development projects. Illustrate your explanation with examples.
2. To be continued.

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Sample examination questions

Each question is marked out of 30.

1. In a patient monitoring system, each patient is monitored by an analog device which measures factors such as pulse, temperature, blood pressure, and skin resistance. The program reads these factors on a periodic basis (specified for each patient) and stores the factors in a database. For each patient, safe ranges for each factor are also specified by medical staff. If a factor falls outside a patient's safe range, or if an analog device fails, the nurses' station is notified. The following diagram, derived from the patient monitoring problem, shows a subproblem that is concerned with the editing of periods and ranges by the medical staff.
   
   
   1. In the above diagram, explain why one of the connectors from the elliptical box has an arrowhead while the other does not. (3 marks)
   2. The line label "m" is annotated as follows:
      MS! {EnterPeriod, EnterRange, ...}
      Explain the significance of the various parts of this annotation. (3 marks)
   3. Explain why the label "m" is attached to two lines in the diagram. (2 marks)
   4. Explain why the given subproblem is called a projection rather than a partition of the main problem. (5 marks)
   5. Give a critique of the use of problem diagrams like the one above for communicating with potential users of the system during requirements gathering. (7 marks)
2. 1. Explain what is meant by a software development process model. (4 marks)
   2. Give a brief account of the waterfall model of software development. (5 marks)
   3. Explain what is meant by a risk reduction measure. (4 marks)
   4. Give a critical appraisal of the waterfall model as a risk reduction measure, identifying the threats that it aims at reducing. (7 marks)

3. A machine is required to act as a branch controller for a supermarket. Each branch will have its own controller, linked to a central computer.

   Authorised staff can use a standard screen and keyboard connected to the store controller to display and edit the descriptions and prices of the bar coded items offered for sale on the shelves. The controller records the prices, sales and stock levels of the bar-coded items.

   There might be as many as twenty-four checkout stations in a store, and each checkout station is connected to the store controller. Each checkout station has a till in which the cash is kept, a barcode scanner, a scale for weighing vegetables and other loose goods, a display that shows the description and price of the item just scanned or weighed, and a printer for printing the items and prices that the customer has bought. There is a keyboard for keying in the codes of items that will not scan properly, and for entering the amount tendered by the customer. The controller is notified as each item is scanned or weighed or keyed, and of the amount tendered. The controller must print a receipt for each customer detailing the items purchased, their prices, the total to be paid, the amount tendered, and the change to be given. The controller also unlocks the till when the operator enters the amount tendered. The till has a spring lock that locks it each time the lid is closed.

   The controller transmits a daily order to the warehouse. The way in which this order depends on the day's sales is complex, and will not be described here, though it is well-known to the supermarket's managers. The format of the order document is already defined.

   Authorised staff can display stock levels for all the items, and edit them on receipt of a delivery from the warehouse.

   1. From this information construct a problem diagram. (7 marks)
   2. Identify a subproblem that fits one of Jackson's five problem frames, say which frame it is, and give the problem diagram for it. (4 marks)
   3. What concerns should you have about the role of the central computer? Explain. (2 marks)
   4. Write a short critical assessment of the contention that there is nothing to be gained from using Problem Fames that could not be obtained from Object-Oriented Analysis. (7 marks)
4. 1. Explain what is meant by a cardinal aim of a project. (2 marks)
   2. Explain the difference between pre-emptive risk reduction measures and reactive risk reduction measures. (4 marks)
   3. As part of a computer science class, students are expected to work in teams to produce a back end processor for the property market. The back end will provide a number of generic functions for recording the details of clients and of properties, searching for properties according to various criteria, recording offers made, recording sales completed, and producing various managements reports. The back end is intended to support a number of different front ends, each of which will be used by a different firm of estate agents, and will provide the agent's own brand image. The deliverables on which the students will be assessed are a conceptual model of the view of property sales management supported by the back end, a specification of the back end in the formal specification language VDM-SL, a Java implementation of the back end, a test harness for exercising the back end functions, and instructions for installing the system, for operating the test harness, and for writing applications to use the back end. The development process to be used is approximately the waterfall model, and various milestones have been set at which various work products have to be available for review. The development team has been put together more or less at random. The members have some experience of Java, but have little development expertise. They are attending a course of twice-weekly lectures given over the period of the project. For VDM-SL, a consultant is available to give advice, and to review the VDM-SL specification after the first few weeks of the project. Each team has a non-technical project manager. For this project state four cardinal aims, and for one of the cardinal aims construct a cause-effect tree of at least 7 and not more than 10 nodes. (6 marks)
   4. Give a critical account of the V-process model as a quality control mechanism. (8 marks)
5. A microchip computer is required to control a digital electronic speedometer and odometer in a car. One of the car's rear wheels generates pulses as it rotates. The computer can detect these pulses, and must use them to set the current speed and total number of miles travelled in the two visible counters on the car's fascia. The underlying registers of the counters are shared by the computer and the visible display. Here is the problem diagram for the problem.

   

   The connectors in the diagram are annotated as follows:

   • a: CR! { WheelPulse }
   • b: OM! { IncreaseSpeed, IncreaseDistance, DecreaseSpeed, DecreaseDistance }
   • c: CR! { Speed, CumulativeDistance }
   • d: FD! { SpeedCount, DistanceCount }
   1. In the above problem diagram, which are the given domains? (3 marks)
   2. In the above problem diagram, explain the significance of the elliptical box marked "Counters agree with travel", and explain why one of the connectors from the elliptical box has an arrowhead while the other does not. (4 marks)
   3. What phenomena are shared between the odometer microchip and the fascia display, and which of these domains controls these phenomena? (3 marks)
   4. Which of Jackson's five basic frames is the best fit for this problem? (2 marks)
   5. Explain what is meant by an initialisation concern and an overrun concern. Illustrate your answer with reference to this problem. (8 marks)
6. 1. What is meant by quality when it refers to a software product? (4 marks)
      
   2. Explain the difference between analysis and testing as methods for checking quality attributes of a software product. (4 marks)
      Illustrate your answer with reference to the following requirements:
      1. Changing the language in which messages are displayed on the screen does not require changes to the procedural code. (4 marks)
         
      2. The system can be initialised on a machine with only 64 megabytes of memory. (4 marks)
      3. When a request is made to withdraw more than the current balance from a savings account, the withdrawal is not made, and a message is sent to the user. (4 marks)
      4. When the system is initialised, a list of valid commands is displayed on the operator's station. (4 marks)
   3. In the V-process model, what is meant by an acceptance test? What is the role of the acceptance test in product quality assurance? (6 marks)
7. To be continued.

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