Studies Business 2002 Paper 8 Question 5 (a) Distinguish between top-down, bottom-up and spiral (rapid prototype) development methodologies. Illustrate your answer with reference to an example of designing a building. Top down methodologies start with a high-level view of the problem, and, at each iteration break it down into smaller steps, until the individual module is capable of implementation. For example a software task might, at the top level, be decomposed into - Initialise - Do work - Clean up And then Initialise be further decomposed into Initialise static variables Initialise dynamic variables
Parnas claimed that each level of decomposition should embody a single design decision for each module. Bottom up, by contrast, starts at the lowest level of decomposition and designs successively larger aggregations, with each layer implemented using the "metamachine" of the layer beneath. This design style is used, for example, for objectoriented programming To use a building analogy, top-down starts with the grand vision of the building and adds detail, whilst bottom-up starts with basic modules, such as doors and windows, then builds room-modules, eventually combining them make the building design. One problem with both top-down and bottom-up approaches is that they are juggernauts: a mistaken decision earlier in the process is hard to correct later. Another problem is that the level of detail makes it difficult to comprehend the design at intermediate stages. To overcome these difficulties spiral development or rapid prototype methodology was developed by Bohm and others. Here a small subset of the project is first developed, and then incremental additions are made to this stable core. For example the major screens of the user interface could be mocked up, and then progressively implemented. The advantage of this method is that here is always a stable fall-back position, and good visibility, assuring better real-world fit.. In terms of a building, the analogy might be, as most buildings of any age are, collection a of extensions and alterations to the original smaller core. (b) You are in charge of commissioning the design of a new building, such as the new Computer Laboratory building. Draw up a high-level GANTT chart for this task up to the letting of the building contract. [10 marks]
(N.B. Marking guidelines: Candidates are not expected to know the details of how to design a building, but should demonstrate that they know what a GANTT chart is, and using common sense produce a reasonable and logical sequence, including periods for user consultation. The exact details and time estimates in the chart aren't important. Marking the critical path would be a bonus..) 4th Quarter 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter 1st Quarter ID Task Name Duration Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan 1 Prepare Brief 160 days
2 3 4 5 6 7 8 9
Gather Requirements Consult users Consult others Gather constraints Budget Prepare brief Check Brief with users
60 days 3 mons 3 mons 60 days 1 mon 2 mons 1 mon 1 mon 1 mon 200 days 3 mons 1 mon 3 mons 6 mons 220 days 4 mons 4 mons 4 mons 3 mons 1 mon 1 mon 1 mon 2 ...