2Recall the Four Steps of Problem Solving* OrientPlanExecuteTestThese apply to any kind of problem, not just spreadsheet development, programming, or process design, but we will focus on those kinds of problems in this class* [Carlson and Bloom, “The Cyclic Nature of Problem Solving: An Emergent Multi-Dimensional Problem Solving Framework”, Educational Studies in Mathematics, Vol. 58 Number 1, 2005]
3SpecificationWe’ve talked about doing the requirements (the orient phase… what we want to have happen)Now we’re ready to talk about the specification or design phase (the planning phase… how it should happen)Our tool for developing and communicating a design is the flow chart
4Problem-Solving Techniques Flowcharts are a visual technique for designing a process (figuring out how to do something)Before we learn about flow charts (a technique for “how” problems), let’s look at a couple of useful visual techniques for solving other kinds of problemsFor more on the ideas here, see Dan Roam’s website,
5“When” ProblemsSuppose we want to make a master plan showing team leaders when each step of a complex process they are directing and coordinating will take placeWhen -> timelineSince we need to convey a large amount of precise information, a Gantt Chart is an appropriate visual tool
9How Many/How Much Suppose we need to answer how many/how much Bar charts are often usedPie charts are another option (controversial because it is harder to compare pie slices than bars)There are plenty of interesting and clever variations… such as the word usage chart (next slide)
10Variation on Bar Chart Word Usage in 2008 McCain Speech
11Example: Seeing the Market These charts are much more informative than a list of prices.These charts show how much versus when.They give much more insight than a numericallist of prices.
12Flowcharts: “How”Flowcharts are a visual tool for specifying a processThey can be as high level or as detailed as we need them to beThey use symbols and arrows to represent steps and choices
13Flowchart Symbols Flowline: Connects symbols and indicates the flow of logic. It is a one way street.Input/Output: Data to be read or displayedare described inside.Terminal: Represents the beginning or end ofa task.Processing: The process description is includedinside the symbol.Decision: Used for logic/comparison operations. Hasone entry and two exits.
15Simple ProcessesA simple process has no decisions in it; you always do it the same wayAs a result, its flowchart is just a straight line of boxes connected by arrowsExample: most recipes, instruction sheets with assemble-it-yourself furniture, simple calculations
16Simple Process: Compound Interest Goal: Given a number N of years, an amount P of money (principal), and an annual interest rate R, calculate the total amount of money T you will have after P is invested for N years at rate R, using interest which is compounded annually. T = P(1+R)NTest 1: P = 100, N = 1, R = 5% (.05): 105Test 2: P = 100, N = 7, R = .05: 140Test 3: P = 0, N = 7, R = .05: 0Test 4: P = 100, N = 7, R = 0: 100Test 5: P = 100, N = 0, R = .05: 100
17Just for interest P = 100, N = 20, R = .05 gives 265 By contrast, simple interest at 5 percent gives $5 per year, so after 20 years you have a total of $200; after 30 you have $250.If R is, say, 8%, the difference is even more striking.
18Storing InformationIn this process we have to keep track of some information, like how much principal we have, what the interest rate is, etc.We’ll use variables to store these values
19VariablesA variable is a name used to refer to a quantity whose value can changeYou can think of a variable as the name of a container that holds a value(A constant is a name for a quantity whose value does not change.)A spreadsheet cell is a good example of a container that can hold a value
20Math Variables vs Programming/Spreadsheet Variables In math, a variable is used in an equation to represent some single quantity.If we are given the equation 3x = x + 6, we can solve this equation for x and get x = 3. You can check the correctness by substituting 3 for x on each side and seeing that you get the same value (9)An “equation” like x = x + 1 would be meaningless; it has no solution
21Programming Variables Programming variables and spreadsheet locations are a place to store a value, which can changeThe assignment statement x = 4 means to store the value 4 in location x. It is not really an equation, though it looks like oneThe pair of assignments,x = 4x = x + 1means to first store a 4 in location x, and then take the current contents (4), add 1, and store the result (5) in location x. The order of the statements is extremely important.
22Compound Interest Calculator beginR = annual rateN = number of yearsP = principalWe used variables R, N, P, and T.T = P*(1+R)^NArrows in a flowchart are likeone-way streets; once you godown one, you can’t back upOutput Tend
23Example SpreadsheetThe spreadsheet called Interest Calculator 1 has this formula in itLet’s take a minute to see how to build this spreadsheet
24AlgorithmThe interest rate calculator is an example of a simple algorithm: a type of effective method in which a list of well-defined instructions for completing a task will, when given an initial state, proceed through a well-defined series of steps, eventually terminating in an end-stateThought to be named for Al-Khwārizmī, Persian astronomer and mathematician
26User InterfaceThe first step in the design is often to think about the user interfaceWhat does the user interact with?What are the possible events that can occur?
27Candy Machine Objects and Events Coin slotUser inserts a coinCandy slotOpens so a piece of candy can come outHandleThe user attempts to turn the handleCoin receptacleIt can be full or not fullThese are all the objects in the requirements that have eventsHowever: how does the machine know if there is a correct coin in the coin slot? Or any coin at all? It looks like the handle turning mechanism needs to be able to check some things.
28Handle FunctionsThe turn of the handle tries to send a coin to the coin receptacle. The handle only allows the correct coins through and won’t turn otherwiseThe handle should not turn if the coin receptacle is fullThe designer is someone like a mechanical engineer who can figure out whether we can build a handle mechanism like this within our budget, and what the tradeoffs areWe won’t look at the mechanical aspect of this, but we can express the logical flow of the solution in a flow chart
29Turning the HandleThe next slide shows the flowchart for the event where someone tries to turn the handle of the candy machineIt shows the use of the begin/end, conditional, and process step boxes
30Handle Flowchart start begin attempt to turn handle no correct coin in slot?yesnoreceptaclehas room?yeshandle does not turnhandle turnscoin goes into receptaclecandy slot opensend
31From Use Cases to Flowchart In the candy machine example, we have several objects, but only one event that requires a process: trying to turn the handleThe use cases were various complete scenarios of an interaction with the machineWe abstracted information from several use cases to design the handle turning eventWe use the tests to make sure we put the pieces together correctly
32Event-Driven DesignThis type of design is called “event driven” because it works by analyzing what the events are in the process and what should happen as a result of each eventThis has turned out to be a highly effective way of designing processes