Software Engineering - Universitetet i...

Software Development Method by Jan Pettersen Nytun, page 1

Software Engineering

A systematic approach to the analysis, design, implementation

and maintenance of software.


Software Engineering Methods

• Most methods consist of both a modelling language and a process (who is doing what and when).

• The modelling language - the notation - typically includes some visual language (different types of diagrams).

• A tool to support the method is also crucial.


UML Is Not a Process • The UML is intentionally process independent - Different domain

may require different processes.

• But the UML authors promote a development process that is (examples of methods: The Unified Software Development Process and RUP)

• use-case-driven

• incremental and iterative

• architecture centric


• The Management Process - schedules work, deliveries and resources, monitor progress.

• The management process is controlling The Development Process – which is about developing software from requirements.

• Some methods contains both processes, e.g. RUP; others

are mostly development processes, like Catalysis, and others again are management processes, e.g. Dynamic Systems Development Method (DSDM).

Software Development – Two Processes at the Same Time


Heavy-weight And Light-weight Software Processes

• Heavy-weight: – many rules, practices and documents. Example: Standard

RUP (RUP can also be adapted to be a light-weight process).

• Light-weight: – few rules and practices or some that are easy to follow.

• Agile processes are examples of light-weight processes:

– Customer collaboration, responding to change, and focus on working software over documentation.


Software Process Models

• The waterfall model (the “original” version): Requirements are defined first and each phase is ended before moving to the next phase.

• Evolutionary, incremental and iterative development: Requirements are covered gradually and the system is delivered in releases.

The waterfall model of software development

Operation and Maintenance

Design Purpose: Transform the products of

the analysis phase into a more precise description that can be refined into an

executable program.

Implementation Purpose: Transform the products of the

design phase into concepts that can be executed on the computer.

Unit testing.

Testing and Integration System Testing

Requirements Analysis and Capture Purpose: Understand the problem domain and the system to be implemented; communicate with end

users and document the requirements.


Requirements Analysis and Capture - 1

A requirement is a wanted property or behavior of a system.

There are two types of requirements: – Functional – Nonfunctional

From Wikipedia In requirements engineering, a nonfunctional

requirement is a requirement that specifies criteria that can be used to judge the operation of a system, rather than specific behaviours. This should be contrasted with functional requirements that define specific behaviours or functions.


Requirements Analysis and Capture – 2

Functional Requirements

• Functional requirements are often modeled with use cases. – A use case is a short story describing a particular use of

the system; a dialogue between an actor and the system. – Visualized with a use case diagram and a descriptive text!

• Sometimes the user interface is developed or a prototype of the system is made.



Nonfunctional Requirements

• Reliability, Security (observable at run time )

• Testability, maintainability, extensibility and scalability (embodied in the static structure of the software system )

From Wikipedia:



Nonfunctional Requirements

• Examples: – From Wikipedia: A system may be required to present the

user with a display of the number of records in a database. This is a functional requirement. How up-to-date this number needs to be is a non-functional requirement.

– The data should be stored on ASCII files.


Perspectives when it comes to diagrams - one possible way to classify this

• Conceptual: – The concepts of the problem domain are addressed. – Analysis class diagrams – PIMs.

• Specification: – This perspective is typically employed under (early)

design (PIM/PSM). – Interfaces is typically specified, but not the

implementation.

• Implementation: – Class diagrams reflects the classes to implement – PSMs.

closer to the actual software solution


Requirements Analysis and Capture - 4 Domain Model

High Level Conceptual Model

• When you make a domain model you capture/understand the key concepts of the problem domain.

• A domain model is typically visualized with class diagrams.


Car

Person owner

Reality The Domain

Domain Model Concepts From The Domain

DESCRIBE AND UNDERSTAND THE MAIN CONCEPTS WITHIN THE DOMAIN

It is a sort of “thinking model”


• The domain model is less detailed and precise than a design model, e.g., use only a subset of UML, it is not large.

• The same domain model may be used as basis for many applications - so keep the latest version…

• Often there is a glossary of terms that describes the domain classes and other classes. It is important to have a common vocabulary!

Requirements Analysis and Capture - 5 Domain Model -

A Simple OO Model


• Deals with objects and functions that will be programmed.

• Some classes from the Domain Model may be used and extended with operations.

• Classes necessary for the implementation are added.

• The operations can be modeled with sequence diagrams – showing responsibility and interaction.

Design


• The design ends up with an implementation model.

• Automatic or manual mapping to code. • The implementation model is a full specification

of the system. • You can trace back from this model to the

models on higher levels of abstraction.

Design / Implementation Model


• The number of models and which abstraction levels to operation on is a matter of choice – there is no “completely right or wrong“.

• The larger (complex) the system, the more time should be spent on modeling.

Relationships Between The Different Models - 1


• Generally (waterfall):

– You go from more abstract models and end up with implementation models.

– More and more details are added. – You go from more logical models to more

concrete ones. You go from PIMs to PSMs.

– You go from a user point of view to an implementation point of view.

Relationships Between The Different Models - 2


• Domain Model (conceptual model/PIM): – Concepts of the domain (real world classes) – Analysis (requirement)

• Type Model (conceptual/specification model/PIM): – Software types that should be covered by the system – Analysis / preliminary design

• Design Model (specification/PIM/PSM): – Classes (with operations) that will be implemented

• Implementation Model (PSM): – A fully specified system that can be mapped to code

Models – An Example


Problem Domain

Domain Model (an analysis model)

Analysis/Type Model

Design Model

Implementation Model

Code / Implemented System

Map to code

Refine

What is needed in the system

How should the system work

Install

Understand

Static path

use case 1

use case 2

class X

attribut1 ....

<x>does<y>

....

Domain Model

Use Case Texts

Test Cases

use case 1

use case 2

void func1() {......} ......

Methods

class X{ .... }

.....

Coding

class X

attribut1 ....

method()

Design level Diagrams

class Y

attribut1 ....

Sequence Diagrams

obj1

met1() Obj2

Functional path

Use Cases

Requirements Analysis and Capture Design Implementation Testing


Iterative Development • [2] “The waterfall method should only be used

when the requirements are well understood and unlikely to change radically during system development.”

• [1] “As the developer work with a system and understand it better, the model must be iterated at all levels to capture that understanding; it is impossible to understand a large system in a single, linear pass.”


Iterative and incremental development. • Each cycle consist of one or more of the process components

(requirement, design,...), typically only a part (an increment) of the required functionality is implemented through each cycle.

• At each cycle the requirements are verified and validated, this can lead to changed requirements.

• In each cycle the most risky functionality is addressed, the cycle is aimed at eliminating the risk. In this way serious problems is exposed at an early stage, in some cases this can lead to termination of the project.

Requirements / Analysis Design Implementation Testing Requirements .... First Cycle ....


Types of risks • The requirements do not specify the right system.

• The selected technology is not adequate for solving the given types of problems.

• People with the right skills are not available to the project.

• There are political forces that will try to stop or delay the project.


High-level View Of The Development Phases (Unified Modeling Process)

• Inception - the vision of the project is received; initial ideas are discussed; a go-ahead of the project is given.

• Elaboration - the project is planned. Features and architecture is elaborated.

• Construction - the system is developed through a series of iterations.

• Transition - the product is set in production. User training is given.

• Analysis, design,… are called modeling stages, these are not synchronized with the development phases. In each phase the cycle of requirement, design, implementation and testing is preformed repeatedly.


The Development Process

At each phase several complete cycles are possible.

In the beginning requirements capture and analysis is focused, the other process components are more important later on.

Inception

R/A = Requirements / Analysis

D = Design

I = Implementation

T = Testing

R/A R/A R/A D A D I I T I T

Elaboration Construction Transition

Example of development process:

D


References • [1] James Rumbaugh , Ivar Jacobson, Grady Booch: The Unified Modeling Language

Reference Manual. Addison-Wesley, 1999

• [2] Ian Sommerville: Software Engineering, Eight Edition. Addison-Wesley, 2007

• Grady Booch, James Rumbaugh and Ivar Jacobson: The Unified Modeling Language User Guide. Addison-Wesley, 1999

• James Rumbaugh, Michael Blaha, William Premerlani, Frederick Eddy and William Lorenzen: Object-Oriented Modeling and Design. Prentice Hall, 1991

• Martin Fowler with Kendall Scott: UML Distilled. Addison-Wesley, 1997

• Terry Quatrani: Visual Modeling with Rational Rose and UML. Addison-Wesley, 1998

• Ari Jaaksi: A Method for Your First Object-Oriented Project. JOOP - The Journal of Object-Oriented Programming, Januar 1998

• Rational software: http://www.rational.com/uml/documentation.html

http://www.rational.com/uml/documentation.html

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