Lecture Roger Sutton CO357 Computing for Business and Accounting 7: Spreadsheet Documentation 1

CO357 Computing for Business and Accounting Spreadsheet documentation Essentially:  User documentation provides the information required by the user to use the software. Describes  what the software does  how to operate the software  what input data is required  what output is produced  Maintenance documentation provides information on the original analysis and design that led to the implementation and so facilitates future modification. 2 co357lec07

CO357 Computing for Business and Accounting Example E.g. Deterministic Stock Control  A retailer sells just one type of product which costs £ C per unit (unit cost)  Each year the retailer is able to sell A units evenly distributed over the year (annual demand)  The cost of acquiring more of this product from the supplier is £ C o (order cost) irrespective of the size of the order. This represents any administration costs, postage and packing, delivery charge, etc. Further orders are acquired instantaneously  If the retailer were to invest his capital, he might expect a return of r % per annum (cost of capital) If the retailer‘s aim is always to satisfy customer demand, what size order should he place each time to minimise his inventory costs? 3

CO357 Computing for Business and Accounting Example - Problem Analysis Attempting to avoid too much algebra, consider: 1.a product costing £3 per unit 2.demand of 1000 units per year 3.cost of placing an order £10 4.cost of capital 5% per annum 4 If an order of 200 units is placed each time, the average stock level over the year would be 100 units. Stock level Time Accordingly the retailer would have £300 tied up in stock on which he might be earning a return of 5% of £300 = £15. This is called the retailer’s holding cost. (The more stock held the more interest foregone)

CO357 Computing for Business and Accounting Analysis – cont’d Over the year, ordering 200 units each time, would require: orders and cost. This is the order costs. Minimising the number of orders reduces the order costs but necessitates increasing the size of the order and hence the holding costs. The task is to identify the optimal order quantity that minimises the sum of these two costs. Alternatively find q such that is a minimum. 5

CO357 Computing for Business and Accounting User documentation 1.What does the software do? The software determines the cost to a retailer of holding stock for a given order strategy. Further the software determines the economic order quantity, i.e. the order quantity that minimises the cost of inventory 2.How is the software operated? The user enters the parameter values (constants) for the unit cost, annual demand, etc. and the proposed order quantity. What input data is required? unit cost annual demand order cost cost of capital Provide an example with screen shots if necessary. 6

CO357 Computing for Business and Accounting User documentation – cont’d 3.What output is produced? The software will return automatically the cost of inventory for order quantity input, the optimum order quantity and minimum possible cost of inventory. 4.Example data: Output: Cost of inventory = Optimum order quantity = 400 (to nearest hundred) Minimum inventory cost = 50 7 Parameters: unit cost = 3 annual demand = 1000 order cost = 10 cost of capital = 5% Input :order quantity = 200 co357lec07

CO357 Computing for Business and Accounting Maintenance documentation Analysis: Identify the user inputs - what information is to be provided by the user on each occasion the software is used? Identify the constants - what values are used in calculations that might change less often than the input data? Identify what outputs are required - what questions are to be answered? Decide what processing is required to obtain the output from the input values and constants to hand Identify test data - draft out example hand calculations to test the software produced 8

CO357 Computing for Business and Accounting Maintenance documentation Analysis: Identify the user inputs - what information is to be provided by the user on each occasion the software is used? Identify the constants - what values are used in calculations that might change less often than the input data? Identify what outputs are required - what questions are to be answered? Decide what processing is required to obtain the output from the input values and constants to hand Identify test data - draft out example hand calculations to test the software produced 9

CO357 Computing for Business and Accounting Spreadsheet organisation A workbook might comprise several (max 255) worksheets each with a dedicated function, e.g. depending on the size of the task  Contents - indicates the contents of subsequent worksheets  Description - describes the facilities/ functions that the spreadsheet is able to carry out  Input - contains instructions or prompts for data entry  Processing - contains calculation or processing areas  Output - Formatted output with possibly initiating input  Documentation - design, formulae and functions used  Control -stores e.g. constants required for input validation, descriptions of macros, etc. 10

CO357 Computing for Business and Accounting Design Spreadsheet map: E.g. depending on size of task 11 Worksheet Description Area defines the title, brief statement of purpose, date written, author Instructions any special considerations for use. Processing Constants Input data Output/results

CO357 Computing for Business and Accounting Design annotation The spreadsheet map should be accompanied by sufficient information to allow another person to implement your spreadsheet. The information should be presented in a methodical way: 1. Worksheets  Record the name of the worksheet and purpose of each worksheet used.  Indicate the standard column width  Indicate the default font, size,colour, background colour 2.Ranges - within each worksheet Indicate any non-standard column widths. For each two-dimensional range  Specify the range address  Record any name given  Provide a description of the range Repeat for each one-dimensional range 12

CO357 Computing for Business and Accounting Design annotation – cont’d 3.Cells - as appropriate For each range specified  Identify particular/typical cell(s) by cell address  Record any name given  Indicate the data type and format  Indicate any starting value or formula contained in the cell  Provide any additional information or comment Identifying worksheets, ranges and cells provides different levels of abstraction. Moving from one level to another reveals increasing detail. This is a common feature of structured analysis and design methodologies 13 co357lec07