Lecture 3
ANALYSIS AND DESIGN
PB007 Software Engineering I
Faculty of Informatics, Masaryk University
Fall 2018
1© Barbora Bühnová
Outline
² Software analysis and design
² Structured vs. object-oriented methods
² Object-oriented analysis in UML
² Objects and classes
² Finding analysis classes
2Chapter 7 Design and implementation
Software Analysis and Design
Lecture 3/Part 1
3Chapter 7 Design and implementation
Analysis, design and implementation
² Software development
§ analysis, design and implementation
§ the stage in the software engineering
process at which an executable
software system is developed
There are two ways of constructing a
software design: One way is to make it so
simple that there are obviously no
deficiencies, and the other way is to make it
so complicated that there are no obvious
deficiencies.
– C.A.R. Hoare
4Chapter 7 Design and implementation
PROBLEM
Requirements
System
SOLUTION
Analysis
Design
Implementation
Analysis, design and implementation
² Software analysis, design and implementation are
invariably inter-leaved with blurred border in between.
§ Software analysis is a creative activity in
which you identify software processes,
entities (objects) and their relationships.
§ Software design refines analytical models
with implementation details.
§ Implementation is the process of realizing
the design as a program.
² Where is the line between the problem domain
and the solution domain?
² Why do we distinguish them when the line is blurred anyway?
5Chapter 7 Design and implementation
PROBLEM
Requirements
System
SOLUTION
Analysis
Design
Implementation
Process stages
² There is a variety of different design processes that
depend on the organization using the process.
² Common activities in these processes include:
1. Define the context and modes of use of the system;
2. Draft the system architecture;
3. Identify the principal system processes and entities;
4. Develop design models;
5. Specify component/object interfaces;
6. Finalize system architecture.
² What activities are part of analysis/design/implementation?
6Chapter 7 Design and implementation
1. System context and interactions
² Understanding the relationships between the
software and its external environment is essential for
deciding
§ how to provide the required system functionality and
§ how to structure the system to communicate with its
environment.
² Understanding of the context also lets you establish the
boundaries of the system.
§ Setting the system boundaries helps you decide what features
are implemented in the system being designed and what
features are in other associated systems.
7Chapter 7 Design and implementation
Context and interaction models
² A system context model is a structural model that demonstrates the
users and other systems in the environment of the system being
developed.
² An interaction model is a dynamic model that shows how the
system interacts with its environment as it is used.
² Do we really need visual models for that? What is their role in A&D?
8Chapter 7 Design and implementation
2. Architectural design
² Starts system analysis and/or finishes system design.
§ Is it the same architecture design in both cases?
² Involves identifying major system components and
their communications.
§ Represents the link between requirements specification and
analysis/design processes.
§ E.g. The weather station is composed of independent
subsystems that communicate via (asynchronous) messaging.
² Software architecture gives answers to the most
expensive questions.
– heard from O. Krajíček
9Chapter 6 Architectural design
High-level architecture of the weather
station
10Chapter 7 Design and implementation
Architectural abstraction
² Architecture in the small (analysis) is concerned with
the architecture of individual programs.
§ At this level, we are concerned with the way that an individual
program is decomposed into components.
² Architecture in the large (design) is concerned with
the architecture of complex enterprise systems that
include other systems, programs, and program
components.
§ These systems are distributed over different computers, which
may be owned and managed by different companies.
11Chapter 6 Architectural design
Advantages of explicit architecture
² Stakeholder communication and project planning
§ Architecture may be used to facilitate the discussion by system
stakeholders.
² System analysis
§ Means that analysis of whether the system can meet its nonfunctional
requirements is possible.
² System documentation
§ Via a complete system model that shows the different
components in a system, their interfaces and their connections.
² Large-scale reuse
§ The architecture may be reusable across a range of systems
§ Product-line architectures may be developed.
12Chapter 6 Architectural design
3. System analysis
² Identification of system entities (object classes in
object-oriented analysis) playing the key roles in the
system’s problem domain, and their relationships.
² Distillation and documentation of key system
processes.
² System analysis is a difficult creative activity.
§ There is no 'magic formula' for good analysis. It relies on the
skill, experience and domain knowledge of system analysts.
² Object/relationships/processes identification is an
iterative process. You are unlikely to get it right first
time.
13Chapter 7 Design and implementation
Weather station object classes
14Chapter 7 Design and implementation
5. Design models
² Design models refine analysis models with the
information required to communicate and document
the intended implementation of the system.
§ E.g. Dependencies, interfaces, data-access classes, GUI
classes.
² Static models describe the static structure of the system
in terms of system entities and relationships.
§ Can you list some static UML diagrams?
² Dynamic models describe the dynamic interactions
between entities.
§ Can you list some dynamic UML diagrams?
15Chapter 7 Design and implementation
Key points
² The process of analysis and design includes activities to design the
system architecture, identify entities in the system, describe the
design using different models and document the component
interfaces.
² Software analysis is a creative activity in which you identify
software processes, entities (objects) and their relationships.
² Software design refines analytical models with implementation
details.
² Software analysis and design are inter-leaved activities.
16Chapter 7 Design and implementation
Structured vs. Object-Oriented Methods
Lecture 3/Part 2
17
© Strukturovaná analýza systémů
by J. Ráček
Fundamental views of software systems
² Function oriented view
§ System as a set of interacting functions. Functional
transformations based in processes, interconnected with data
and control flows.
² Data oriented view
§ Searches for fundamental data structures in the system.
Functional aspect of the system (i.e. data transformation) is less
significant.
² Object oriented view
§ System as a set of interacting objects, encapsulating both the
data and operations performed on the data.
18
© Strukturovaná analýza systémů
by J. Ráček
Structured vs. object-oriented analysis
² Structured analysis
§ Driven by the function oriented view, in synergy with data
oriented view, through the concept of functional decomposition.
² Object-oriented analysis
§ Driven by the object oriented view.
Do they have anything in common?
19
© Strukturovaná analýza systémů
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Structured analysis and design
² Divides a project on small, well defined activities and
defines the order and interaction of the activities.
² Using hierarchical graphical techniques, resulting in a
detailed structured specification, which can be
understood by both system engineers and users.
² Effective in project structuring to smaller parts, which
simplifies time and effort estimates, deliverables control
and project management as such.
² Aimed at increasing system quality.
20
© Strukturovaná analýza systémů
by J. Ráček
Functional decomposition
21
System
context
Level 0
processes
Level 1
processes
Data
dictionary
Basic-process
specification
© Strukturovaná analýza systémů
by J. Ráček
Structured methods
² DeMarco: Structured Analysis and System Specification
(SASS)
² Gane-Sarson: Logical Modelling (LM)
² Yourdon: Modern Structured Analysis (YMSA)
§ Concentrates on the data and control flow of system processes
and sub-processes.
² Structured Systems Analysis and Design Method
(SSADM)
§ Physical design, logical process design and logical data design
22
© Strukturovaná analýza systémů
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Core notations of structured methods
² Context diagram
§ Models system boundary and environment.
² Data flow diagram (DFD)
§ Models the system as a network of processes completing
designated functions and accessing system data.
² Entity relationship diagram (ERD)
§ Models system’s data.
² State diagram (STD)
§ Models system states and actions guarding transitions from one
state to another.
23
© Strukturovaná analýza systémů
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Examplary method (Gane-Sarson)
1. Define system context and create initial system DFD.
2. Draft initial data model (ERD).
3. Analyze data entities and relationships into final ERD.
4. Refine DFD according to the ERD data model (create
logical process model).
5. Decompose logical process model into procedural
elements.
6. Specify the details of each individual procedural
element.
24
© Strukturovaná analýza systémů
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Object-oriented analysis and design
² Software engineering approach that models a system as
a group of interacting objects.
² Each object represents some entity of interest in the
system being modeled, and is characterized by its class,
its state (data elements), and its behavior.
² Various models can be created to show the static
structure, dynamic behavior, and run-time deployment of
these collaborating objects.
² There is a number of different methods, defining the
ordering of modeling activities. The modeling notation
uses to be unified (UML).
25Chapter 7 Design and implementation
Object-oriented methods
² Jim Rumbaugh: Object Modelling Technique (OMT)
² Coad-Yourdon: Method for Object-Oriented Analysis
(OOA)
² Jacobson: Object-Oriented Software Engineering (OOSE)
² Kruchten et al.: Rational Unified Process (RUP)
§ Risk-driven iterations, component-based, with continuous quality
verification and change management.
² Booch-Jacobson-Rumbaugh: Unified Process (UP)
§ Simplified non-commercial version of RUP maintained by Object
Management Group (OMG).
26Chapter 7 Design and implementation
UML notation for object-oriented methods
² External perspective
§ Use case diagram
² Structural perspective
§ Class diagram, Object diagram, Component diagram, Package
diagram, Deployment diagram, Composite structure diagram
² Interaction perspective
§ Sequence diagram, Communication diagram, Interaction
overview diagram, Timing diagram
² Behavioral perspective
§ Activity diagram, State diagram
27Chapter 7 Design and implementation
Examplary method (Unified Process,
analysis and design excerpt)
1. Requirements
§ System boundary, actors and requirements modelling with Use
Case diagram.
2. Analysis
§ Identification of analysis classes, relationships, inheritance and
polymorphism, and their documentation with a Class diagram.
§ Use Case realization with Interaction and Activity diagrams.
3. Design
§ Design classes, interfaces and components, resulting in refined
Class diagrams and Component diagrams.
§ Detailed Use Case realization with Interaction and State
diagrams.
28Chapter 7 Design and implementation
Key points
29
© Strukturovaná analýza systémů
by J. Ráček
Structured analysis Object-oriented analysis
System boundary Context diagram Use case diagram
Functionality Data flow diagram Activity diagram
Interaction diagrams
Data Entity-relationship diagram Class and Object diagram
Control State diagram State diagram
² Structured methods
§ System as a set of nested processes accessing system data.
² Object-oriented methods
§ System as a set of interacting objects (functions and data).
Object-Oriented Analysis in UML
Lecture 3/Part 3
30© Clear View Training 2010 v2.6
© Clear View Training 2010 v2.6 31
Analysis objects and classes
What are objects?
² Objects consist of data and function packaged together
in a reusable unit. Objects encapsulate data.
² Every object is an instance of some class which defines
the common set of features (attributes and operations)
shared by all of its instances.
² Objects have:
§ Attribute values – the data part
§ Operations – the behaviour part
number = "1243"
owner = "Jim Erl"
balance = 300
deposit()
withdraw()
getOwner()
setOwner()
Bank Account
Object
attribute values
operations
© Clear View Training 2010 v2.6 32
All objects have
² Identity: Each object has its own unique identity and can
be accessed by a unique handle
§ Distinguish two cars of the same type and one car referenced
from two places.
² State: This is the actual data values stored in an object
at any point in time
§ On and off for a light bulb (one attribute).
§ On + busy, on + idle, off for a printer (two attributes).
² Behaviour: The set of operations that an object can
perform
© Clear View Training 2010 v2.6 33
Messaging
² In OO systems, objects send messages to each other over links
² These messages cause an object to invoke an operation
Bank Object Account Object
withdraw( 150.00 )
the Bank object sends the
message “withdraw 150.00” to
an Account object.
the Account object responds by
invoking its withdraw operation. This
operation decrements the account
balance by 150.00.
message
© Clear View Training 2010 v2.6 34
UML Object Syntax
² All objects of a particular class have the same set of operations. They are not shown
on the object diagram, they are shown on the class diagram (see later)
² Attribute types are often omitted to simplify the diagram
² Naming: object and attribute names in lowerCamelCase, class names in UpperCamelCase
jimsAccount : Account
accountNumber : String = "1234567"
owner : String = "Jim Arlow"
balance : double = 300.00
attribute
name
attribute
compartment
name
compartment
attribute
type
attribute
value
object
name
class
name
jimsAccount : Account
jimsAccount
: Account
object and
class name
object name
only
class name
only
variants
(N.B. we've omitted the attribute compartment)
an anonymous object
object identifier
(must be underlined)
© Clear View Training 2010 v2.6 35
What are classes?
² Every object is an instance of one class - the class describes the
"type" of the object
² Classes allow us to model sets of objects that have the same set of
features - a class acts as a template for objects:
§ The class determines the structure (set of features) of all objects of that
class
§ All objects of a class must have the same set of operations, must have
the same attributes, but may have different attribute values
² Classification is one of the most important ways we have of
organising our view of the world
² Think of classes as being like:
§ Rubber stamps
§ Cookie cutters
class
object
© Clear View Training 2010 v2.6 36
Exercise - how many classes?
© Clear View Training 2010 v2.6 37
Classes and objects
² Objects are instances of classes.
² Instantiation is the creation of
new instances of model elements.
² Most classes provide special
operations called constructors
to create instances of
that class.
² These operations
have class-scope
i.e. they belong to
the class itself rather
than to objects of the classs.
withdraw()
deposit()
Account
accountNumber : String
owner : String
balance : double
objects
class
ilasAccount:Account
accountNumber : "803"
owner : "Ila"
balance : 310.00
fabsAccount:Account
accountNumber : "802"
owner : "Fab"
balance : 1000.00
JimsAccount:Account
accountNumber : "801"
owner : "Jim"
balance : 300.00
«instantiate»«instantiate» «instantiate»
© Clear View Training 2010 v2.6 38
UML class notation
² Classes are named in UpperCamelCase – avoid abbreviations!
² Use descriptive names that are nouns or noun phrases
Window
+size : Area = (100,100)
#visibility : Boolean = false
-colorRGB : Integer [3]
-defaultSize : Rectangle
-maximumSize : Rectangle
-xptr : XWindow*
+create()
+hide()
+display( location : Point )
-attachXWindow( xwin : XWindow*)
{author = Jim,
status = tested}
name
compartment
attribute
compartment
operation
compartment
class name tagged values
initial
values
class scope
(static) operation
visibility
adornment
Window
size : Area
visibility : Boolean
hide()
display()
Analytical class
Design class
© Clear View Training 2010 v2.6 39
Attribute compartment
Structure
visibility name : type multiplicity = initialValue
Visibility
+ public
- private
# protected
~ package
Type
Integer, Real, Boolean, String, Class
Multiplicity
[3] specific number of elements
[0..1] optional
* array, list
Initial values
Window
+size : Area = (100,100)
#visibility : Boolean = false
-colorRGB : Integer [3]
-defaultSize : Rectangle
-maximumSize : Rectangle
-xptr : XWindow*
+create()
+hide()
+display( location : Point )
-attachXWindow( xwin : XWindow*)
{author = Jim,
status = tested}
mandatory
attribute
compartment
Operation signature
visibility name ( direction parameterName : parameterType = default, ...) : returnType
Direction
in input value, default
out repository for system output
inout modifiable input value
return operation return value(s)
Scope
instance scope defaults
class scope underlined
Constructors
generic constructor name or
Java/C++ standard
+BankAccount( aNumber : int )
© Clear View Training 2010 v2.6 40
Operation compartment
parameter list or a list r1, r2,… rn
BankAccount
-accountNumber : int
-count : int = 0
+create( aNumber : int)
+getNumber() : int
-incrementCount()
+getCount() : int
operation
compartment
© Clear View Training 2010 v2.6 41
Key points
² We have looked at objects and classes and examined
the relationship between them
² We have explored the UML syntax for modelling classes
including:
§ Attributes
§ Operations
² We have seen that scope controls access
§ Class scope attributes are shared by all objects of the class and
are useful as counters
§ Attributes and operations are normally instance scope
§ We can use class scope operations for constructor and
destructors
Finding Analysis Classes
Lecture 3/Part 4
42© Clear View Training 2010 v2.6
© Clear View Training 2010 v2.6 43
What are Analysis classes?
² Analysis classes represent a crisp
abstraction in the problem domain
§ They may ultimately be refined
into one or more design classes
² Analysis classes have:
§ A very “high level” set of
attributes. They indicate the
attributes that the design classes
might have.
§ Operations that specify at a high
level the key services that the
class must offer. In Design, they
will become actual,
implementable, operations.
BankAccount
name : String
address
balance : double
deposit()
withdraw()
calculateInterest()
class name
attributes
operations
Specify attribute
types if you know
what they are.
© Clear View Training 2010 v2.6 44
What makes a good analysis class?
² Its name reflects its intent
² It is a crisp abstraction that models one specific
element of the problem domain
§ It maps onto a clearly identifiable feature of the problem domain
² It has high cohesion
§ Cohesion is the degree to which a class models a single
abstraction
§ Cohesion is the degree to which the responsibilities of the class
are semantically related
² It has low coupling
§ Coupling is the degree to which one class depends on others
© Clear View Training 2010 v2.6 45
Rules of thumb
² 3 to 5 operations per class
² Each class collaborates with others
² Beware many very small classes
² Beware few but very large classes
² Beware of “functoids”
² Beware of “omnipotent” classes
² Avoid deep inheritance trees
A responsibility is a
contract or obligation
of a class - it resolves
into operations and
attributes
© Clear View Training 2010 v2.6 46
² Perform noun/verb analysis on documents:
§ Nouns are candidate classes
§ Verbs are candidate responsibilities
What documents can be studied?
² Perform CRC card analysis
§ Class, Responsibilities and Collaborators
§ A two phase brainstorming technique using sticky notes – first
brainstorm and then analyse the dat
Finding classes
Responsibilities:
Class Name: BankAccount
Collaborators:
Maintain balance Bankthings the
class does
things the
class works
with
© Clear View Training 2010 v2.6 47
Other sources of classes
² Physical objects
² Paperwork, forms
§ Be careful when relying on processes that need to change
² Known interfaces to the outside world
² Conceptual entities that form a cohesive abstraction
² With all techniques, beware of spurious classes
§ Look for synonyms - different words that mean the same
§ Look for homonyms - the same word meaning different things
© Clear View Training 2010 v2.6 48
Key points
² We’ve looked at what constitutes a well-formed analysis
class
² We have looked at two analysis techniques for finding
analysis classes:
§ Noun verb analysis of use cases, requirements, glossary and
other relevant documentation
§ CRC analysis