CS3320::CH111 OBJECT-ORIENTED ANALYSIS Chapter 11

CS3320::CH112 OBJECT-ORIENTED ANALYSIS (OOA) Semi-formal specification technique Several methods –Booch, OMT, OOSE, Objectory--Essentially equivalent –Nowadays--represent OOA using UML (Unified Modeling Language)

CS3320::CH113 THE THREE STEPS OF OOA 1. Use-case Modeling –Determine how the various results are computed by the product (without regard to sequencing) –Largely action-oriented 2. Class Modeling (“Object Modeling”) –Determine the classes and their attributes –Purely data-oriented 3. Dynamic Modeling –Determine the actions performed by and to each class –Purely action-oriented

CS3320::CH114 Elevator Problem:OOA 1. Use-case Modeling Use cases: Describe the behavior of the system as seen from actor’s point of view. Actors: external entities that interact with the system (e.g. A system adm, a bank customer, a bank teller, a central database, etc.) A Scenario: a concise description of how an actor may interact with the system –a scenario is an instance of a use case

CS3320::CH Use-case Modeling Identify the actors Identify a list of "typical" scenarios to get insight into the system’s behavior Identify use-cases –a use-case specifies all possible scenarios for a given functionality. –a use case is initiated by an actor. –A use case represents a flow of events thru the system.

CS3320::CH116 Elevator Problem: OOA

CS3320::CH117 Normal Scenario

CS3320::CH118 Abnormal Scenario

CS3320::CH Object Modeling The object model describes the real-world object classes of the systems and their relationship to each other with an entity- relationship diagram It shows the static structure of the system. 1. Identify classes/objects 2. Identify associations between objects 3. Identify attributes of objects 4. Represent them using an entity-relationship diagram 5. Prepare a data dictionary

CS3320::CH1110 Identifying Object Classes An Object is an instance of a class that consists of –Data (attributes, state variables, instance variables, fields, data members) –Actions (methods, member functions) An object has a state (represented by data members) that changes during execution.

CS3320::CH1111 Identifying Object Classes Objects include physical entities (house, employees, button, etc.) and concepts (payment schedule, seating assignment, trajectory, etc.) Avoid computer implementation constructs (an array, a linked list, a binary tree, etc.) Don’t be concerned with operations at this points.

CS3320::CH1112 Identifying Object Classes Two approaches –Deduce from use cases and their scenarios often many scenarios too many candidate classes –Noun Extraction The two approaches are complementary

CS3320::CH1113 Noun Extraction Stage 1: Concise Problem Definition Define product in a single sentence Buttons in elevators and floors are to be used to control motion of n elevators in building with m floors. Stage 2: Incorporate constraints buttons illuminate when pressed to request elevator to stop at specific floor; illumination is cancelled when request has been satisfied. If elevator has no requests, it remains at its current floor with its doors closed.

CS3320::CH1114 Noun Extraction Stage 3: Identify nouns. Nouns: buttons, elevator, floor, movement, building, illumination, door floor, building, door are outside the problem boundary ==>excluded Movement, illumination are abstract nouns ==>excluded (may become attributes) Candidate classes: elevator, button Subclasses: Elevator button and floor button

CS3320::CH1115 Noun Extraction

CS3320::CH1116 Identify Associations An association is any dependency between two or more classes. Example: –Person works-for Company –User has Home Directory –Directory contains Files contains and part-of are special types of associations called aggregation Inheritance is also a special type of association.

CS3320::CH1117 Identifying Associations Problem statement –location phrases: next to, contained in, etc –communication: talk to –ownership phrases: has, part of –satisfaction of some condition: works for, married to, manages Some depend on knowledge of application domain.

CS3320::CH1118 Identifying Associations Example: Buttons in elevators and floors are to be used to control motion of n elevators in building with m floors. –Buttons control elevators –There are two types of buttons: floor buttons and elevator buttons –However, buttons do not really control elevator they simply communicate with it.

CS3320::CH1119 Identify Associations Identify association multiplicity: –1 to 1 –1 to many –Many to many Identify aggregations Identify inheritance relations

CS3320::CH1120 First Iteration of Class Model Problem: buttons do not communicate directly with elevator==> class Elevator Controller

CS3320::CH1121 Second Iteration of Class Model

CS3320::CH1122 Identify Attributes Attributes are properties of individual objects Problem Statement: –Correspond to nouns followed by possessive phrase: collar of the car, position of the cursor, salary of the employee, etc. Attributes are less likely to occur in statement of the problem. Knowledge of application domain. Try to get only the most important attributes at this stage. Others can be added later

CS3320::CH1123 Prepare Data Dictionary Write a paragraph describing each object class. Described the scope of the class within the current problem Describe associations and attributes Data dictionaries also include description of operations.

CS3320::CH1124 CRC Cards Used since 1989 for OOA For each class, fill in card showing –name of Class –Responsibility : functionality –Collaboration: list of classes it invokes

CS3320::CH1125 Elevator Controller--CRC 1. Turn on elevator button Totally unacceptable in OOA

CS3320::CH1126 Elevator Controller--CRC 1. Turn on Elevator Button Should be 1. Send message to Elevator Button to turn on button What about ? 5. Open elevator doors Note: Elevator doors have a state that changes during execution (class characteristic) ==> add class Elevator Doors

CS3320::CH1127 Elevator Controller--CRC

CS3320::CH Dynamic Modeling The dynamic model shows the time-dependent behavior of the system Aim: Produce a UML state diagram for each object class. A state diagram is less formal than an FSM –States, events, and conditions

CS3320::CH1129 States and Events The state of an object are defined by the values of its attributes. Objects change state when stimulated by other objects or external actors. A event is an individual stimulus from one object to another. The response to an event by the object receiving it can include a change of state or the sending of an another event (to the original object or another object)

CS3320::CH1130 Events An event is something that happens at a point in time: user depresses left-button, phone receiver lifted, call is routed, input string entered. An event has no duration: assumed to be instantaneous An event coveys information from one object to another –signal that something has occurred –Send data values: left mouse-button pushed (location)

CS3320::CH1131 Example Draw a state diagram for a phone line

CS3320::CH1132 Conditions A condition is a Boolean function of an object values. Example: –Temperature is below freezing –Floor button is lit –No cars on N/S left lanes A condition is valid over an interval of time Generally, a condition indicates the state of another object in the system.

CS3320::CH1133 Conditions Conditions are used as guards on transitions: –A transition fires when its event occurs, only if the guard condition is true –When you go out in the morning (event), if the temperature is below freezing (condition), then put on your gloves (next state)

CS3320::CH1134 Traffic Light Controller Straight N/S or W/E After N/S times-out, –if there are cars on N/S left lane, N/E left- turn signal is turned on –else straight W/E light is turned on Same for W/E left-lane

CS3320::CH1135 N/S may go straight N/S may turn left W/E may go straight W/E may turn left Time-out [cars in W/E left lane] Time-out [cars in N/S left lane] Time-out [No cars in N/S left lane] Time-out [No cars in W/E left lane]

CS3320::CH1136 Operations--Activities & Actions Operations are performed in response to states or events: Activity: an operation that takes time to complete. –Continuous operations: display a picture –Sequential operations that terminate after an interval of time: performing a computation, play a recorded message

CS3320::CH1137 Activities –An activity continues until complete or interrupted by an event that causes transition to a another state –e.g. ringing a telephone bell –Activities are associated with states State1 do: activity1 do: activity2

CS3320::CH1138 Operations--Activities & Actions Action: is associated with an event Instantaneous: duration is insignificant compared to the resolution of the state diagram –e.g. when callee hangs-up disconnect phone line Changing attribute values: –e.g. increment count when some event occurs.

CS3320::CH1139 Summary of Notation State 1 do: activity 1 do: activity 2 State 2 do: activity... Event [condition]/action

CS3320::CH1140

CS3320::CH1141 CASE Tools for OOA Phase Paradigm Plus Software through Pictures Rose