*Object-Oriented Design (Schach Chap 14) Goal: Design product in terms of objects identified during OOA OOD consists of four steps: Construct interaction diagrams for each scenario. Two types: Collaboration Diagrams (Spatial), Sequence Diagrams (Temporal) Develop detailed class diagram Design the product in terms of clients of objects Proceed to detailed design Result of our Elevator System OOA: A UML Class Diagram 1..3 Constitute “High-Level” Design

*Step 1 of OOD: Interaction Diagrams Construct interaction diagrams for each scenario, focus is on the objects and the messages passed between them. “Passing a message” between objects really means having one object invoke a public member function of another object. An interaction is implemented by a group of objects that collaborate by exchanging messages. Two variants of UML Interaction Diagrams: Collaboration/Communication and Sequence Diagrams

*Collaboration Diagrams: spatial representation Focus is on the relationships between objects Goal is to understand Structure of Design’s components Timing info is obscure, messages numbered to indicate sending order Example: Consider making a hotel reservation

Example: Elevator Collaboration Diagram Sally is on the 10th floor and presses a floor button. The elevator arrives from the ground floor to pick her up.

*Sequence Diagrams: temporal representation Focus is on message broadcast chronology of interactions between objects from a temporal standpoint. An object is represented by a rectangle and a vertical bar. Message sending order indicated by position on axis. Again, consider making a hotel reservation

Example: Elevator Sequence Diagram Sally is on the 10th floor and presses a floor button. The elevator arrives from the ground floor to pick her up.

Connection between Scenarios & Sequence Diagrams Example of a Normal Use Scenario

A UML Collaboration Diagram A Collaboration Diagram is equivalent to its corresponding Sequence Diagram

MFKA UML Sequence Diagram ICE: Produce a UML Sequence Diagram for the Marine Field Kitchen Assistant scenario of “Finding a recipe for chili that includes chipotle powder, scaling it for 200 Marines per meal, and generating a grocery list for a week’s worth of chili (to be eaten 3 times a day).”

*Step 2 of OOD: Construct Detailed Class Diagram A well-structured Interaction Diagram gives very specific information on what responsibilities a class should have. Main question, do we assign an action to a class or to a client of that class? Information hiding Reducing copies of an action Responsibility-driven design Examples close doors assigned to Elevator Doors move one floor down assigned to Elevator Typical: Class at head of arrow on Interaction Diagram gets tasked with the labeled responsibility, and implements it as a method.

*Construct Detailed Class Diagram Consider class Elevator Controller If User wants to log and update requests, needs requests attribute Needs methods: log request, update requests, request is pending Detailed: As used here means that all method names, and (as a by-product) attributes ID’d by designer, are represented on the diagram

*Step 3 of OOD: Determine Clients of Objects Design Product in Terms of Clients of Objects to determine which objects should create other objects Draw a single arrow from each object to a client of that object Objects that are not clients of any object have to be initiated, probably upon system launch, Additional methods may be needed. elevator controller needs method elevator control loop so that elevator application can call it. This Completes High-Level Design for OOD!

*Step 4 of OOD: Perform Detailed Design Detailed design of method elevator controller loop, draws heavily from prior UML diagrams. Design Team: Should not do too much: Detailed design should not become complete code Should not do too little: It is essential for detailed design to fully indicate how all functionality is met. So, how to verify we are done with detailed design?

*ICE: Detailed Design ICE: Take an assigned class, and Complete the detailed UML class diagram of assigned class (to include its methods and attributes), and Give the pseudo-code for the most complex method in the class. We will pick a QA volunteer to walk thru the chipotle chili scenario and make sure each class has the methods the sequence diagram expects of it. Detailed design of method elevator controller loop, draws heavily from prior UML diagrams. Design Team: Should not do too much: Detailed design should not become complete code Should not do too little: It is essential for detailed design to fully indicate how all functionality is met. So, what should detailed design’s output be?

*Testing During the Design Phase Design itself must be correct No logic faults Interface for each class fully defined. Design reviews. Purpose is to show that Design correctly reflects Specification. How can this be shown?

*Case Tools for OOD Computer Aided Software Engineering (CASE) tools Examples of CASE tools: Software through Pictures, Rational Rose Visual Paradigm Built around data dictionary Screen, report generators What automated support could be provided by a case tool that represents OOD using UML?

*Metrics for OOD What Metrics can be used to describe various aspects of the Design? One is McCabe’s Cyclomatic complexity. Measure based on # of controlflow decisions, can apply to pseudo-code. the number of binary decisions plus 1, a metric of design quality, the lower the M the better What other aspects of a Design can be Measured? Advantage: Easy to compute, can be automated Disadvantage: Measures control complexity only, does not measure data complexity.

Recap: Relationships Between UML Diagrams OOA OOD