Outline Business – Assign Process & Decision Models (individual assignment) – Q’s on project draft models? Activities – Case Study 2 discussion – Decision tables and trees – Decision exercise

Making Decision Criteria Explicit Decisions are part of many workflows. A decision is needed when there is more than one possible course of action and you must choose which one to take. Decision tables/trees model: the possible actions or choices the conditions or criteria that are considered in making the decision the possible values of the criteria the combinations of values that determine when each action is taken. The possible values should be mutually exclusive and exhaustive. Mutually exclusive means that there is no overlap between values. Probability of rain ≤ 50% Probability of rain ≥ 50% These are not mutually exclusive: if the probability = 50%, which value is correct? Exhaustive means that any possible value of the condition is represented. Probability of rain < 50% Probability of ran > 50% These are not exhaustive: if the probability = 50%, which value is correct?

Example: Should I take my umbrella? For example, I need to decide if I should take my umbrella when I leave the house. It depends on what the weather is now, and what the forecast for rain is for the rest of the day. possible actions: take my umbrella or don't take my umbrella conditions: current weather and rain forecast possible values: current weather {raining, not raining} forecast for rain: {probability of rain ≤ 50%, probability of rain > 50% Once the actions, conditions, and values are defined, I need to work through each of the possible combinations of values to determine whether I will take my umbrella. If it isn't raining and the probability of rain ≤ 50%, then I won't take my umbrella. If it is currently raining, it doesn't matter what the forecast is, I'll take my umbrella. What will I do if it isn't raining and the probability of rain > 50%? (What would you do?)

Decision Table or Tree The table and tree are semantically equivalent, but they present the information in different ways. I find the table useful to work out what combinations of criteria lead to each action. The tree is especially useful if the order in which the criteria are considered can streamline the decision process. In the umbrella example, if it is currently raining, it doesn't matter what the forecast is, I will take my umbrella. So if I look outside first, I know what to do. (If it isn't raining, I would still have to check the forecast.) If I check the forecast first, then sometimes it won't have been necessary (i.e., if it is raining).

Use a decision table/tree to… help you understand how a client makes a decision help the client understand how he/she makes a decision – sometimes the client "just knows what to do" work out what all the possible actions really are zoom in on a decision diamond in a process model – another type of leveling – keeps the process model less cluttered document the decision criteria so decisions are made consistently – over time, by different people

But… If a decision is truly based on judgment, experience, or "instinct" – The decision model may help you reveal that is how it works. – The decision model won't be helpful in documenting or enforcing consistency. For example, an editor reads manuscripts and decides whether to accept or reject them for publication. – How does the editor know what is likely to sell? – Some editors "just know".

Decision Table Conditions and possible values Possible actions or choices Each column shows a combination of values at the top, and the action that will be taken at the bottom. You should specify the action for each possible combination of values.

Decision Tree zoo museum art show weather? kids? museum no yes nice raining nice raining Conditions can be phrased as questions. Possible values are represented by branches in the tree. Start at the left, and take the branch that corresponds to the value. Start here Question 1Question 2 Actions

Decision Example: What should we do on Saturday? We could go to the zoo, we could go to the natural history museum, or we could go to the art show. It all depends whether the kids are with us, and the weather. If we have the kids and the weather is nice, we’ll go to the zoo. If we have the kids and it’s raining, we’ll go to the museum. If the kids are with their friends and it’s nice, we’ll go to the art show, but if it’s raining, we’ll go to the museum. What are the conditions, or variables? What are the possible values? What are the possible actions?

Decision Table Do we have the kids? How's the weather? What are our choices? Have kids, nice weather, we'll go to the zoo. Don't have the kids, raining, we'll go to the museum.

Alternate Table Form

Decision Tree 1 zoo museum art show weather? kids? museum no yes nice raining nice raining Questions are presented in the order in which they are given in the narrative. How many do you have to answer if it’s raining?

Decision Tree 2 zoo museum art show weather? kids? no yes nice raining Questions are presented in a different order. How many do you have to answer if it’s raining?