1. Process Design (Specification)

2. Recall the Four Steps of Problem Solving*
Orient
Plan
Execute
Test
These 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]

3. Specification
We’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

4. Problem-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 problems
For more on the ideas here, see Dan Roam’s website,

5. “When” Problems
Suppose we want to make a master plan showing team leaders when each step of a complex process they are directing and coordinating will take place
When -> timeline
Since we need to convey a large amount of precise information, a Gantt Chart is an appropriate visual tool

6. Gantt Chart Example

7. GANTT with Dependencies

8. Baseline GANTT (shows comparison, change)

9. How Many/How Much Suppose we need to answer how many/how much
Bar charts are often used
Pie 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)

10. Variation on Bar Chart Word Usage in 2008 McCain Speech

11. Example: 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 numerical
list of prices.

12. Flowcharts: “How”
Flowcharts are a visual tool for specifying a process
They can be as high level or as detailed as we need them to be
They use symbols and arrows to represent steps and choices

13. Flowchart Symbols Flowline: Connects symbols and indicates the
flow of logic. It is a one way street.
Input/Output: Data to be read or displayed
are described inside.
Terminal: Represents the beginning or end of
a task.
Processing: The process description is included
inside the symbol.
Decision: Used for logic/comparison operations. Has
one entry and two exits.

14. One more…
Continuation

15. Simple Processes
A simple process has no decisions in it; you always do it the same way
As a result, its flowchart is just a straight line of boxes connected by arrows
Example: most recipes, instruction sheets with assemble-it-yourself furniture, simple calculations

16. Simple 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)N
Test 1: P = 100, N = 1, R = 5% (.05): 105
Test 2: P = 100, N = 7, R = .05: 140
Test 3: P = 0, N = 7, R = .05: 0
Test 4: P = 100, N = 7, R = 0: 100
Test 5: P = 100, N = 0, R = .05: 100

17. Just 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.

18. Storing Information
In 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

19. Variables
A variable is a name used to refer to a quantity whose value can change
You 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

20. Math 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

21. Programming Variables
Programming variables and spreadsheet locations are a place to store a value, which can change
The assignment statement x = 4 means to store the value 4 in location x. It is not really an equation, though it looks like one
The pair of assignments,
x = 4
x = x + 1
means 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.

22. Compound Interest Calculator
begin
R = annual rate
N = number of years
P = principal
We used variables R, N, P, and T.
T = P*(1+R)^N
Arrows in a flowchart are like
one-way streets; once you go
down one, you can’t back up
Output T
end

23. Example Spreadsheet
The spreadsheet called Interest Calculator 1 has this formula in it
Let’s take a minute to see how to build this spreadsheet

24. Algorithm
The 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-state
Thought to be named for Al-Khwārizmī, Persian astronomer and mathematician

25. Back to the Candy Machine…

26. User Interface
The first step in the design is often to think about the user interface
What does the user interact with?
What are the possible events that can occur?

27. Candy Machine Objects and Events
Coin slot
User inserts a coin
Candy slot
Opens so a piece of candy can come out
Handle
The user attempts to turn the handle
Coin receptacle
It can be full or not full
These are all the objects in the requirements that have events
However: 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.

28. Handle Functions
The 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 otherwise
The handle should not turn if the coin receptacle is full
The 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 are
We won’t look at the mechanical aspect of this, but we can express the logical flow of the solution in a flow chart

29. Turning the Handle
The next slide shows the flowchart for the event where someone tries to turn the handle of the candy machine
It shows the use of the begin/end, conditional, and process step boxes

30. Handle Flowchart start begin attempt to turn handle no correct
coin in slot?
yes no
receptacle
has room?
yes
handle does not turn
handle turns
coin goes into receptacle
candy slot opens
end

31. From 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 handle
The use cases were various complete scenarios of an interaction with the machine
We abstracted information from several use cases to design the handle turning event
We use the tests to make sure we put the pieces together correctly

32. Event-Driven Design
This 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 event
This has turned out to be a highly effective way of designing processes