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Bernd Bruegge & Allen Dutoit Object-Oriented Software Engineering: Conquering Complex and Changing Systems 2

Software Lifecycle Activities

Application

Domain Objects

SubSystems

class...class...class...

Implementation

Domain Objects

SourceCode

Test Cases

?

Expressed in Terms Of

Structured By

Implemented

ByRealized By Verified By

SystemDesign

ObjectDesign

Implemen-tation Testing

class....?

RequirementsElicitation

Use CaseModel

RequirementsAnalysis


Outline

1. Overview of Analysis Model Inputs - requirements model (use cases) Outputs or parts of the Analysis Model

dynamic model Develop preliminary sequence diagrams to illustrate the interaction

between objects Develop state diagrams for objects with interesting behavior

static model Develop preliminary object and class diagrams showing the structure

of the system Heuristics to help create the Analysis Model


Requirements Model, Analysis Model, Design Models 1. Analyze the problem statement

Identify functional requirements Identify nonfunctional requirements Identify constraints (pseudo requirements)

2. Build the functional model Develop use cases to illustrate functionality requirements

3. Build the dynamic model Develop sequence diagrams to illustrate the interaction between objects Develop state diagrams for objects with interesting behavior

4. Build the static model Develop object and class diagrams showing the structure of the system

5. Use the analysis model (static and dynamic) to create the architecture and the (detailed) design models


Analysis: UML Activity Diagram

Reviewmodel

Consolidatemodel

Defineentity

Defineboundary

Definecontrol

Defineinteractions

Defineassociations

Defineattributes

Definenontrivialbehavior

Defineparticipating

Defineuse cases

objects

objects objectsobjects


Analysis Model: - model structure and behavior of objects-start with objects seen by from client’s perspective Structure - Static model Behavior - Dynamic model Static and dynamic modeling need to be done at the same time

Creating the Analysis Model Input model: requirements model (use cases) Output models: static and dynamic models

Subsequently, the analysis model is the input for creating the architecture and (detailed) design models


Analysis Model

Steps during dynamic modeling use case event flows (normal, alternate) heuristic: start with 1 sequence diagram per use case

if alternate flows are complex, then consider using separate sequence diagrams for each alternate flow

Steps during static modeling 1. Object/Class identification

heuristic: start with the nouns in the use cases event flows 2. Find the attributes

heuristic: nouns 3. Find the methods

Basic methods include Create, Read, Update, Delete (CRUD) 4. Find the associations between classes

Association, generalization, aggregation, composition 5. Find the multiplicity relationship between classes


Static Modeling with UML Classes Associations (Relations)

Part of- Hierarchy (Aggregation) Kind of-Hierarchy (Generalization)

Attributes Detection of attributes Application specific Attributes in one system can be classes in another system

Operations/Signature/Methods Generic methods Domain specific methods


Dynamic Modeling with UML Diagrams for dynamic modeling Interaction diagrams

Sequence Diagram: Dynamic behavior of a set of objects arranged in time sequence. Good for real-time specifications and complex scenarios

Collaboration Diagram : Shows the relationship among objects. Does not show time

Statecharts: A state machine that describes the response of an object of a given

class to the receipt of outside stimuli (Events). Activity Diagram:

Special type of statechart where all states are action states


Heuristics or Guidelines - Where do we start?

Class Identification Identify the boundary (or interface) objects of the system Identify the important entity objects in the system Identify control objects in the system Class identification is crucial to object-oriented modeling Basic assumption:

1. We can find the classes for a new software system (Forward Engineering)

2. We can identify the classes in an existing system (Reverse Engineering)

Why can we do this? Philosophy, science, experimental evidence


Object vs. Class Object (instance): Exactly one thing

The lecture on September 7 on Software Engineering from 9:00 -10:20

A class describes a group of objects with similar properties IETM, Author, Corrosion, Work order

Class diagram: A graphic notation for modeling classes and their relationships ("associations")


How do you find classes?

Learn about problem domain: Observe your client Apply general world knowledge and intuition Apply design patterns Try to establish a taxonomy Take the flow of events and find participating objects in use

cases Do a textual analysis of scenario or flow of events (Abbott

Textual Analysis, 1983)Nouns are good candidates for classes

Heuristic (for 6354): start with the points in blue


Mapping parts of speech to object model components [Abbot 1983]

Part of speech Model component Example

Proper noun object Jim Smith

Improper noun class Toy, doll

Doing verb method Buy, recommend

being verb inheritance is-a (kind-of)

having verb aggregation has an

modal verb constraint must be

adjective attribute 3 years old

transitive verb method enter

intransitive verb method (event) depends on


Example: Use Case – from Dental Office System- input for creating the Analysis Model

Title: Search for Supplier InformationPreconditions: Dental Office System has been initializedPostconditions: If the search is successful, then the supplier information is

displayed. If the search is not successful, then an error message is displayed.

Normal Flow: The Operator requests to search for supplier. The Operator may perform a

keyword search using the boolean operators “not”, “and”, and “or”. The Operator may enter up to three keywords

The system displays the name, phone number, fax number, and address of the suppliers that match the search criteria.

Alternate Flow The Operator requests to search for supplier. The Operator may perform a

keyword search using the boolean operators “not”, “and”, and “or”. If no matches are found, then the system displays an error message to the

Operator.


Example: Use Case – from Dental Office System// Circle the nouns (focus on the normal and alternate flows)Title: Search for Supplier InformationPreconditions: Dental Office System has been initializedPostconditions: If the search is successful, then the supplier information is displayed. If the search is not

successful, then an error message is displayed.

Normal Flow:1. The Operator requests to search for supplier. The Operator may perform

a keyword search using the boolean operators “not”, “and”, and “or”. The Operator may enter up to three keywords

2. The system displays the name, phone number, fax number, and address of the suppliers that match the search criteria to the Operator.

Alternate Flow1. The Operator requests to search for supplier. The Operator may perform

a keyword search using the boolean operators “not”, “and”, and “or”. 2. If no matches are found, then the system displays an error message to the

Operator.// I started here with proper nouns (actors). // Exercise: identify nouns/possible objects and attributes


UML: Class and Object Diagrams

Supplier

ACME Floss:Supplier

Vogue:Supplier

:Supplier

Class Diagram

Object Diagram

AnonymousObject


phone: string

Attributes and Values

name:stringaddress: string

Supplier ACME Floss:Supplier

fax: string phone: 972-883-4216

name:ACME Floss Inc.address: 1607 N. Floyd RdRichardson, Texas, USA

fax: 972-883-2349


Operation, Signature or Method?

Operation: A function or transformation applied to objects in a class. All objects in a class share the same operations (Analysis Phase)

Signature: Number & types of arguments, type of result value. All methods of a class have the same signature (Object Design Phase)

Method: Implementation of an operation for a class (Implementation Phase)

Workorder

File_name: StringSize_in_bytes: integerLast_update: dateStickies: array[max]

print()delete()open()close()write()read()


Links and Associations

Links and associations establish relationships among objects and classes.

Link: A connection between two object instances. A link is an instance of an association

Association: Bidirectional mapping. One-to-one, many-to-one, one-to-many, An association describes a set of links like a class describes a set of

objects. Generalization, aggregation, composition, and others


Object Types Entity Objects

Represent the persistent information tracked by the system (Application domain objects, “Business objects”)

Boundary Objects Represent the interaction between the user and the system

Control Objects: Represent the control tasks performed by the system

Having three types of objects leads to models that are more resilient to change. The boundary of a system changes more likely than the control The control of the system change more likely than the application

domain


Example: Use Case – from Dental Office System// Circle the nouns (focus on the normal and alternate flows)Title: Search for Supplier InformationPreconditions: Dental Office System has been initializedPostconditions: If the search is successful, then the supplier information is displayed. If the search is not

successful, then an error message is displayed.

Normal Flow: The Operator requests to search for supplier. The Operator may perform

a keyword search using the boolean operators “not”, “and”, and “or”. The Operator may enter up to three keywords.

The system displays the name, phone number, fax number, and address of the suppliers that match the search criteria to the Operator.

Alternate Flow The Operator requests to search for supplier. The Operator may perform

a keyword search using the boolean operators “not”, “and”, and “or”. If no matches are found, then the system displays an error message to the

Operator.// Supplier is an entity object; what are name, phone, fax, and address?// Boundary objects? Control objects?


TIP

If you organize your boundary objects on the left, then this model is going to be organized in a similar way to your sequence diagrams

Example: Dental Office System- describe as classes- if needed, generalize the objects

<<entity>>Supplier

<<control>>DentalOfficeControl

<<boundary>>GUI

<<entity>>Client

<<control>>...

<<entity>>Dental Office


Static Modeling in Practice: Encourage Brainstorming

Find New Objects (nouns in use case)

Iterate on Names, Attributes and Methods

Find Associations between Classes, Links between Objects

Label the associations, links

Determine the multiplicity of the associations

Iteratively refine the model•Don’t put too many objects/classes into the same package: 7+-2

Generalize as a Class


Example: Dental Office System- a place to start

<<entity>>Supplier

<<boundary>>DentalOfficeGUIBoundary

<<entity>>Client

<<control>>DentalOfficeControl

<<entity>>Appointment

nameaddressphonefax

addmodifysearchdelete


Dynamic Modeling

Definition of dynamic model: A collection of sequence diagrams; one state chart diagram for

each class with important dynamic behavior. Purpose:

Identify signatures for the object model Verify the use cases

How do we do this? Start with use case (or scenario) Model interaction between objects to create sequence diagram Model dynamic behavior of single objects to create Statechart

diagram


Sequence Diagram

From the flow of events in the use case proceed to the sequence diagram

A sequence diagram is a graphical description of objects participating in a use case

Relation to object identification: Objects/classes have already been identified during object

modeling New objects are identified as a result of dynamic modeling

Find/correct errors of omission Heuristic:

Events in a use case are externally visible The events map to interactions between an actor and a boundary

object in the sequence diagram For each interaction in the use case there is an interaction in the

sequence diagram between actors and boundary objects


Heuristics for Sequence Diagrams

Layout: 1st column: Should correspond to the actor who initiated the use case 2nd column: often a boundary object 3rd column: often a control object that manages the rest of the use

case Creation:

When is each object created? Highly related to use case that initializes the system

Access: Entity objects are accessed by control and boundary objects, Entity objects should never call boundary or control objects: This

makes it easier to share entity objects across use cases and makes entity objects resilient against technology-induced changes in boundary objects.


Sequence Diagram- a place to start

:DentalOfficeControl

ACME Floss:Supplier

Request Search for Suppliers

:Operator

Supplier name, phone, fax, address

Penultimate Floss:Supplier

Search for Supplier

Search for Supplier Response

:DentalOfficeGUIBoundary

create()

...Collection of suppliers’ name, phone, fax, address

Enter searchcriteria

search()

analysis

Documents

analysis model dynamic

analysis model input

analysis model static

model structure

functional model

analysis model steps

behavior of objects

system static model