V. Goal Diagrams

Goals and AND/OR Trreess
Softgoals
Building Goal Diagrams
How and Why Questions

Presentation: N.C. Danh ©2004 John Mylopoulos

Goals

▪Goals represent business objectives for the new system and its operating environment.

▪For example,

✔“Fulfill every book request” (Library organization)

✔“Produce 1M MacG5s within a year” (Apple), or,

✔“Serve more passengers” (TTC)

Lifecycle Models Alternatives for Satisfying Goals ▪ An AND-goal is satisfied if all of its subgoals are; an OR-goal is satisfied if at least one its subgoals is.

▪ An alternative (solution) to a root goal G consists of a set of leaf goals which together satisfy G.

▪ There are 24 alternatives for the goal of the previous slide. 4

Softgoals

▪These are goals that are used as criteria for comparing alternative solutions for other goals.

E.g.,Higher profits[ProductionUnit3], Better service, Satisfied customer, User-friendly[Interface, 2]

Portable[Module4]

Goal Relationships

▪We will use more than AND- and OR-relationships: ✔+ -- one goal contributes positively towards the fulfillment of another goal; ✔- -- one goal contributes negatively towards the fulfillment of another goal; ✔++ (--) -- one goal subsumes/negates another, i.e., if the first goal is fulfilled, the second is fulfilled/denied;

▪With these enhancements, we can build goal models which could be useful for strategic business analysis or requirements analysis.

Alternatives for Satisfying Goals

▪An alternative (solution) to the fulfillment of a goal G consists of one or more leaf goals which together fulfill the root goal. ▪A goal model defines a space of alternatives for the fulfillment of its root goal.

▪An alternative A1 is better than A2 in fulfilling goal G with respect to softgoals G1, G2,… if A1’s net contributions to G1, G2,… (e.g., positive minus negative contributions) is greater than that of A2.

▪ In general, goals and softgoals can be contradictory. Given a set of root goals and softgoals, there may not be an optimal solution [Simon68]. Hence the search for good-enough solutions.

Building Goal Diagrams

▪ Start from one or more goals and/or softgoals G1, G2,… , Gn which need to be fulfilled together.

▪ Analyze each, looking for ways to fulfill it through AND- or OR decompositions, or through other refinements which contribute positively (How questions).

▪ Continue this process until there is enough positive support to fulfill all root nodes. At this point you have n disconnected goal trees T(G1), T(G2),…,T(Gn).

▪ Identify positive and negative inter-tree influences, i.e., positive or negative relationships between goals g, g’ which belong to different goal trees.

▪ Repeat the analysis to see if root goals are fulfilled; if so, done, else continue the analysis.

Lifecycle Models