One to Three

CHAPTER ONE

Introduction to Software Engineering

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Why Software Engineering?• Software development is hard! • Important to distinguish “easy” systems (one developer, one

user, experimental use only) from “hard” systems (multiple developers, multiple users, products)

• Experience with “easy” systems is misleading– One person techniques do not scale up

• Analogy with bridge building:– Over a stream = easy, one person job– Over River Severn … ? (the techniques do not scale)

• The problem is complexity• Many sources, but size is key:

– UNIX contains 4 million lines of code– Windows 2000 contains 108 lines of code

NB: Software engineering is about managing this complexity.2

FAQs about software engineering

• What is – software?– software process?– software engineering?– software process model?

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What is software?• Computer programs and associated documentation

• Software products may be developed for a particular customer or may be developed for a general market

• Software products may be– Generic - developed to be sold to a range of different

customers– Bespoke (custom) - developed for a single customer

according to their specification

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What is software engineering?

Software engineering is an engineering discipline which is concerned with all aspects of software production

Software engineers should – adopt a systematic and organised approach to their

work – use appropriate tools and techniques depending on

• the problem to be solved, • the development constraints and • the resources available

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What is the difference between software engineering and computer science?

Computer Science Software Engineeringis concerned with

Computer science theories are currently insufficient to act as a complete underpinning for software engineering, BUT it is a foundation for practical aspects of software engineering

theory fundamentals

Algorithms, date structures, complexity theory, numerical methods

the practicalities of developing delivering useful software

SE deals with practical problems incomplex software products

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Software Engineering Body of Knowledge

Source: http://www.sei.cmu.edu/pub/documents/99.reports/pdf/99tr004.pdf7

SE history

• SE introduced first in 1968 – conference about “software crisis” when the introduction of third generation computer hardware led more complex software systems then before

• Early approaches based on informal methodologies leading to– Delays in software delivery– Higher costs than initially estimated– Unreliable, difficult to maintain software

• Need for new methods and techniques to manage the production of complex software.

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Software myths

• Management myths– Standards and procedures for building software– Add more programmers if behind the schedule

• Customer myths– A general description of objectives enough to start coding– Requirements may change as the software is flexible

• Practitioner myths– Task accomplished when the program works– Quality assessment when the program is running– Working program the only project deliverable

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Software failures• Therac-25 (1985-1987): six people overexposed during

treatments for cancer• Taurus (1993): the planned automatic transaction settlement

system for London Stock Exchange cancelled after five years of development

• Ariane 5 (1996): roket exploded soon after its launch due error conversion (16 floating point into 16-bit integer)

• The Mars Climate Orbiter assumed to be lost by NASA officials (1999): different measurement systems (Imperial and metric)

• However, important Progresses– Ability to produce more complex software has increased– New technologies have led to new SE approaches– A better understanding of the activities involved in software

development– Effective methods to specify, design and implement software

have been developed– New notations and tools have been produced

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What is a software process?• SP is a set of activities whose goal is the development or evolution of software• Fundamental activities in all software processes are:

– Specification - what the system should do and its development constraints– Development - production of the software system (design and implementation) – Validation - checking that the software is what the customer wants– Evolution - changing the software in response to changing demands

• What is a software process model?: SPM is a simplified representation of a software process, presented from a specific perspective– Examples of process perspectives:

• Workflow perspective: represents inputs, outputs and dependencies • Data-flow perspective: represents data transformation activities • Role/action perspective: represents the roles/activities of the

people involved in software process

– Generic process models• Waterfall• Evolutionary development• Formal transformation• Integration from reusable components 1111

What are the costs of software engineering?

• Roughly 60% of costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs

• Costs vary depending on the type of system being developed and the requirements of system attributes such as performance and system reliability

• Distribution of costs depends on the development model that is used

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What is CASE ? (Computer-Aided Software Engineering)

• Upper-CASE– Tools to support the early process

activities of requirements and design• Lower-CASE

– Tools to support later activities such as programming, debugging and testing

Software systems which are intended to provide automated support for software process activities, such as requirements analysis, system modelling, debugging and testing

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What are the attributes of good software?

• Maintainability– Software must evolve to meet changing needs

• reliability– Software must be trustworthy

• Efficiency– Software should not make wasteful use of system resources

• Usability– Software must be usable by the users for which it was

designed

The software should deliver the required functionality and performance to the user and should be

maintainable, reliable and usable

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What are the key challenges facing software engineering?

Software engineering in the 21st century faces three key challenges:

• Legacy systems– Old, valuable systems must be maintained and updated

• Heterogeneity– Systems are distributed and include

a mix of hardware and software

• Delivery– There is increasing pressure for faster delivery of software

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Object Oriented Concepts• Object-oriented

– Means to organize the software as a collection of discrete objects that incorporate both data structure and behaviour

• Object concepts• We continue to explore the question “what are good

systems like?” by describing the object oriented paradigm.

• We shall answer these questions:– What is an object?– How do objects communicate?– How is an object’s interface defined?– What have objects to do with components?

• Finally we consider inheritance, polymorphism and dynamic binding.

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What is an object?• Conceptually, an object is a thing you can interact with:

– you can send it various messages and – it will react

• How it behaves depends on the current internal state of the object, which may change– For example: as part of the object’s reaction to receiving a

message.• It matters which object you interact with, an object has an

identity which distinguishes it from all other objects.

An object is a thing which has – behaviour, – state and – identity [Grady Booch, 1991]

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State• The state of the object is all the data which it currently encapsulates• An object normally has a number of named attributes (or instance

variables or data members) each of which has a value• Some attributes can be mutable

– An attribute ADDRESS • other attributes may be constant (immutable)

– Date of birth– Identifying number

Behaviour• The way an object acts and reacts, in terms of its state

changes as message passing.• An object understands certain messages,

• it can receive the message and act on them.• The set of messages that the object understands, like the set

of attributes it has, is normally fixed. 1818

Identity - is a little more slippery

• The idea is that objects are not defined just by the current values of their attributes

• An object has continues existence – For example the values of the object’s attributes

could change, perhaps in response to a message, but it would still be the same object.

• An object is normally referred to by a name, but the name of the object is not the same thing as the object, because the same object may have several different names

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Example • Consider an object which we’ll call myClock, which

understands the messages:– reportTime– resetTimeTo(07:43), resetTimeTo(12:30) or indeed more

generally resetTimeTo(newTime) • How does it implements this functionality?• The outside world doesn’t need to know – the information

should be hidden !!! – but perhaps it has an attribute time – Or perhaps it passes these messages on to some other

object, which it knows about, and has the other object deal with messages

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Object: classification• objects with the same data structure (attributes) and behaviour

(operations) are grouped into a class• each class defines a possibly infinite set of objects• Each object is an instance of a class• Each object knows its class• Each instance has its own value for each attribute (state) but

shares the attribute names and operations with other instances of the class– also “static” i.e. class variables

• class encapsulates data and behaviour, hiding implementation details of an object

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Deviation: why have classes????

• Why not just have objects, which have state, behaviour and identity as we require?

• Classes in object oriented languages serve two purposes:– Convenient way of describing a collection (a class) of objects

which have the same properties– In most modern OO languages, classes are used in the same way

that types are used in many other languages• To specify what values are acceptable

Classes and types• Often people think of classes and types as being the same thing

(indeed it is convenient and not often misleading, to do so). However, it’s wrong!

• Remember that a class defines not only what messages an object understand!

• It also defines what the object does in response to the messages. 2222

Object: inheritance• the sharing of attributes and operations among classes based upon

a hierarchical relationship• class can be defined broadly and then refined into successively

finer subclasses• each subclass incorporates or inherit all the properties of its super

class and its own unique properties• Subclass Superclass

– A subclass is an extended, specialized version of its superclass. – It includes the operations and attributes of the superclass, and

possibly some more• Inheritance – warning

– (!) An object class is coupled to its super-classes. Changes made to the attributes or operations in a super-class propagate to all sub-classes 2323

Object: Polymorphism

• it means that the same operation may behave differently on objects of different underlying class while being referenced as a superclass

• OOPL automatically selects the correct method to implement an operation based on the name of the operation (method signature) and the object’s class being implemented

• Polymorphism – exampleVehicle v = null;v = new Car();v.startEngine();v = new Boat();v.startEngine();

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CHAPTER TWO

The Unified Process

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Grady Booch speaks

“People are more important than any process.

Good people with a good process will outperform good people with no process any time.”

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Overview• Unified Process is component based

– system is built using software components interconnected using well defined interfaces

• Unified Process uses Unified Modelling Language (UML)

• Unified Process is distinguished by being• use-case driven• architecture-centric• iterative and incremental

• Based around the 4Ps - People, Project, Product, Process

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Cont...

• Provides disciplined approach to assigning tasks and responsibilities

• Guide for how to use Unified Modelling Language (UML) effectively

• Activities create and maintain (UML) models• Is a configurable process

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Characteristics of Modern Systems

• Volatile business environment subject to constant change - BPR; rapid IS development needed

• Wide range of more complex system types CAD/CAM, GIS, Office Automation, CASE tools

• Increased use of complex data types - text documents, video, sound, graphics, spatial data

• Sophisticated user interfaces (GUIs)• Client-Server environments / distributed systems• Tendency for larger systems with complex and varied

interrelationships among software components

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Effective Deployment of 6 best practices

• Develop software iteratively• Manage requirements• Use component-based architectures• Visually model software• Verify software quality• Control changes to software

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Unified Process : Use Case Driven• Use Case

“A description of a set of sequence of actions, including variants, that a system performs which yields an observable result of

value to a particular actor.”(Jacobson et.al. 1999)

– i.e. A piece of functionality that gives a user a result of value• Development process follows a flow

– proceeds through a series of workflows derived from the use cases

– use cases are specified, designed and are the source for test cases

– they drive system architecture which in turn influences use case selection

– both mature as the development lifecycle continues 31

Unified Process : Architecture-Centric• Software architecture shows different views of the

system being built and embodies the static & dynamic aspects of the system (design framework)

• Also influenced by the computer architecture, operating system, DBMS, network protocols etc.

• Related as function (use case) and form (architecture) • The form must allow the system to evolve from initial

development through future requirements (i.e. the design needs to be flexible)

• Key use cases influence the design of the architecture which may in turn influence development of other use cases

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Unified Process : Iterative and Incremental• Systems development is frequently a large undertaking - may

be divided into several “mini-projects” each of which is an iteration resulting in incremental development of the system

• Iterations must be selected & developed in a planned way i.e. in a logical order - early iterations must offer utility to the users

• iteration based on a group of use cases extending the usability of the system developed so far

• iterations deal with the most important risks first• not all iterations are additive - some replace earlier

“superficial” developments with a more sophisticated and detailed one.

• Concepts of use case driven, architecture centric and iterative & incremental are of equal importance

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An iterative and incremental process

Initial Planning

Analysis & Design

Evaluate

ImplementationManagementEnvironment

Planning

Requirements

DeploymentTest

Each iterationresults in executablerelease

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Benefits of an iterative approach

• Risks are mitigated earlier• Change is more manageable• Higher level of reuse• Project team can learn along the way• Better overall quality

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Life Cycle of the Unified Process• Unified Process repeats over a series of cycles each

concluding with a product release to the users• Each cycle has 4 phases (each with a number of

iterations)• Inception, Elaboration, Construction & Transition

• Delivered products will be described by related models each with “trace” dependencies which chain backwards and forwards

• Use Case Model; Analysis Model; Design Model• Deployment Model; Implementation Model;

Test Model36

Cont…

• The Unified Software Process has four phases:– Inception - Define the scope of project– Elaboration - Plan project, specify features,

baseline architecture– Construction - Build the product– Transition - Transition the product into end

user community

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Core Workflows & Phases

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The 4Ps in Software Development

Process

Product

People Project ToolsParticipants

Template

Automation

Result

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People• People are an integral part of the lifecycle of a software

product, therefore, the process that guides the development must be people orientated

• Actual development process affects people• project feasibility / risk management / team

structure• project schedule / project understandability / sense

of achievement• In modern large and complex systems developers will be

part of a team and will be playing varying and changing roles within it

• Allocation of tasks should maximise project experience40

Project• The first project in the lifecycle (“green-field”

project) develops & releases the initial system; successive cycles extend the life of the system over many releases

• The project team will have to be concerned with:– A sequence of change– A series of iterations– An organisational pattern

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Product• The product is the developed system and comprises:

– Software system (executables, machines, procedures)– Artifacts developed (UML models, prototypes etc.)– A collection of models and relationships between

them• Use Case Model; Analysis Model; Design

Model• Deployment Model; Implementation Model; Test

Model• In the Unified Process the set of models illuminate the

system from the perspective of all people involved in the project (users, developers, project managers) 42

Process• The Unified Software Development Process is a

definition of a complete set of activities to transform users’ requirements through a consistent set of artefacts into a software product

• Unified Process is a template and each project is a process instance of the template (i.e. the template is the definition of the set of activities not the execution of them)

• A process is described in terms of workflows where a workflow is a set of activities with identified artifacts that will be created by those activities

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Static Structure of ProcessesA process describes ‘who, ‘what’, ‘when’ ‘how’

Workers (who) Activities (how)

Artifacts (what)

Workflow (when) - sequence of activities

Designer Use Case Analysis Use Case Design

responsible for

Use caserealisation

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Requirements engineeringRequirements engineering is the process of establishing: •the services that the customer requires from a system •the constraints under which it operates and is developed

Requirements The descriptions of the system services and constraints

that are generated during the requirements engineering process

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What is a requirement?

• It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification

• This is inevitable as requirements may serve a dual function– May be the basis for a bid for a contract - therefore must be

open to interpretation– May be the basis for the contract itself - therefore must be

defined in detail– Both these statements may be called requirements

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Types of requirement• User requirements

– Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers

• System requirements– A structured document setting out detailed

descriptions of the system services. Written as a contract between client and contractor

• Software specification– A detailed software description which can serve as a

basis for a design or implementation. Written for developers 47

Requirements readersClient managersSystem end-usersClient engineersContractor managersSystem architects

System end-usersClient engineersSystem architectsSoftware developers

Client engineers (perhaps)System architectsSoftware developers

User requirements

System requirements

Software designspecification

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Functional and non-functional requirements

• Functional requirements– Statements of services the system should provide,

how the system should react to particular inputs and how the system should behave in particular situations.

• Non-functional requirements– constraints on the services or functions offered by the

system such as timing constraints, constraints on the development process, standards, etc.

• Domain requirements– Requirements that come from the application domain

of the system and that reflect characteristics of that domain

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Functional RequirementsDescribe functionality or system services

• Depend on the type of software, expected users and the type of system where the software is used

• Functional user requirements may be high-level statements of what the system should do BUT functional system requirements should describe the system services in detail

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Examples of functional requirements

• The user shall be able to search either all of the initial set of databases or select a subset from it.

• The system shall provide appropriate viewers for the user to read documents in the document store.

• Every order shall be allocated a unique identifier (ORDER_ID) which the user shall be able to copy to the account’s permanent storage area.

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Requirements imprecision

• Problems arise when requirements are not precisely stated

• Ambiguous requirements may be interpreted in different ways by developers and users

• Consider the term ‘appropriate viewers’– User intention - special purpose viewer for each

different document type– Developer interpretation - Provide a text viewer that

shows the contents of the document

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Requirements completeness and consistency

• In principle requirements should be both complete and consistentComplete– They should include descriptions of all facilities

requiredConsistent– There should be no conflicts or contradictions in the

descriptions of the system facilities• In practice, it is very difficult or impossible to

produce a complete and consistent requirements document

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Non-functional requirementsDefine system properties and constraints e.g. reliability, response time and storage requirements. Constraints are I/O device capability, system representations, etc.

• Process requirements may also be specified mandating a particular CASE system, programming language or development method

• Non-functional requirements may be more critical than functional requirements. If these are not met, the system is useless

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Non-functional Requirements classifications

• Product requirements– Requirements which specify that the delivered product must

behave in a particular way e.g. execution speed, reliability, etc.

• Organisational requirements– Requirements which are a consequence of organisational

policies and procedures e.g. process standards used, implementation requirements, etc.

• External requirements– Requirements which arise from factors which are external to

the system and its development process e.g. interoperability requirements, legislative requirements, etc.

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Examples

• A system goal– The system should be easy to use by experienced

controllers and should be organised in such a way that user errors are minimised.

• A verifiable non-functional requirement– Experienced controllers shall be able to use all the system

functions after a total of two hours training. After this training, the average number of errors made by experienced users shall not exceed two per day.

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Requirements measuresProperty MeasureSpeed Processed transactions/second

User/Event response timeScreen refresh time

Size K BytesNumber of RAM chips

Ease of use Training timeNumber of help frames

Reliability Mean time to failureProbability of unavailabilityRate of failure occurrenceAvailability

Robustness Time to restart after failurePercentage of events causing failureProbability of data corruption on failure

Portability Percentage of target dependent statementsNumber of target systems

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Domain requirements

• Derived from the application domain and describe system characteristics and features that reflect the domain

• May be new functional requirements, constraints on existing requirements or define specific computations

• If domain requirements are not satisfied, the system may be unworkable

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Domain requirements problems

• Understandability– Requirements are expressed in the language of the

application domain– This is often not understood by software engineers

developing the system

• Implicitness.... /indirectness– Domain specialists understand the area so well that they

do not think of making the domain requirements explicit

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User requirements

• Should describe functional and non-functional requirements so that they are understandable by system users who don’t have detailed technical knowledge

• User requirements are defined using natural language, tables and diagrams

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Problems with natural language

• Lack of clarity – Precision is difficult without making the document difficult

to read

• Requirements confusion– Functional and non-functional requirements tend to be

mixed-up

• Requirements amalgamation/ mix– Several different requirements may be expressed together

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System requirements

– More detailed specifications of user requirements

• Serve as a basis for designing the system

• May be used as part of the system contract

• System requirements may be expressed using system models (will be discussed in Chapter 3 & 4)

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The requirements analysis document

• The requirements document is the official statement of what is required of the system developers

• Should include both a definition and a specification of requirements

• It is NOT a design document. As far as possible, it should set of WHAT the system should do rather than HOW it should do it

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CHAPTER THREE

USE Case Design

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Why Use Cases?

• Use Case– A set of scenarios related by a common actor and a goal– A description of sequences of actions performed by a given

system to produce a result for an actor• Use cases specify the expected behavior [what], and not

the exact method of making it happen [how]• Use cases are created based on identified functional

requirements but are not mapped one-to-one to requirements

• Use cases once specified can be denoted using a clear and precise visual modeling language such as UML

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Terms and Concepts• Actors

– Represent roles that humans, hardware devices, or external systems play while interacting with a given system

– They are not part of the system and are situated outside of the system boundary

– Actors may be both at input and output ends of a use case– Primary or Secondary– Notation:

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Cont…• Use case

– A set of interactions between a system and an external person or system that achieves a goal.

– defines a goal-oriented set of interactions between external actors and the system under consideration

– is initiated by a user with a particular goal in mind, and completes successfully when that goal is satisfied

– capture who (actor) does what (interaction) with the system, for what purpose (goal), without dealing with system internals.

– use case steps are written in an easy-to-understand structured narrative using the vocabulary of the domain

– Notation:

Use case Name67

Cont…• Scenarios

– instance of a use case, and represents a single path through the use case

– Specify behavior of use case by description, not modeling• Examples include informal structured text, formal

structured text with conditions, and pseudo-code– Typically specifies:

• How and when the use case starts and ends• Interaction with the actors and the exchange of objects• Flow of events: main / typical (success and exceptional

(failure) flows

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Cont…• Scenarios Example:

– In a human resources system, for the “Hire Employee” use case, the following scenarios may apply:• Typical success scenario: Hire a person from

outside of the company, for example, from another company

• Alternative success scenario: Hire a person from within the same company, for instance, from another division

• Exceptional failure scenario: No qualified person could be hired

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Cont…

• Entry and Exit Conditions– Entry conditions describe the environment under

which the use case is invoked– Exit conditions reflect the impact of the use case on

the environment through its execution• Quality Requirements

– Describe quality attributes in terms of a specific functionality

– For example, requires system response in < 30 seconds

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Cont….• Relationships

– Organize use cases by grouping them in packages– Generalization: The child use case exhibits a more

specific variation in behavior than as specified for its parent

– Include: Common behavior of more than one use case is referenced as a separate instance to avoid repetition

– Extend: Implicit integration of the behavior of another use case by declaring the extension points / events in the base

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Identifying Actors, Use Cases, and Scenarios

• Identifying Actors:– Define system boundary to identify actors correctly– Identify users and systems that depend on the

system’s primary and secondary functionalities– Identify hardware and software platforms with which

the system interacts– Select entities that play distinctly different roles in

the system– Identify as actors external entities with common

goals and direct interaction with the system– Denote actors as nouns

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Cont…• Identifying Use Cases:

– Business / Domain Use Cases:• Interactions between users and the business (or domain)

– System Use Cases:• Interactions between users and the system• One business use cases contains a set of system use cases

– To name the use cases, give it a verb name to show the action that must be performed

• Describe a transaction completely• No description of user interface whatsoever

– Capture use cases during requirements elaboration

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Cont…

• Identifying Scenarios– Extract the functionality that is available to each actor– Establish specific instances and not general

descriptions– Denote situations in the current and future systems– Identify:

• Tasks to be performed by the user and the system• Flow of information to the user and to the system• Events that are conveyed to the user and to the system• For the events flow, name steps in active voice

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UML Use Cases Example

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Courseware System Description• Informal Description:For this case study, the task is of constructing the design elements for a

system that can be used to manage courses and classes for an organization that specializes in providing raining. The name of the system is Courseware System. The organization offers courses in a variety of areas such as learning management techniques and understanding different software languages and technologies. Each course is made up of a set of topics. Tutors in the organization are assigned courses to teach according to the area that they specialize in and their availability. The organization publishes and maintains a calendar of the different courses and the assigns tutors every year. There is a group of course administrators in the organization who manage the courses including course content, assigning courses to tutors, and defining the course schedule. The training organization aims to use the Courseware System to get a better control and visibility to the course management and to also streamline the process of generating and managing schedules for different courses

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Courseware Overview

• The following terms and entities are specific to the system:– Courses and Topics that make up courses– Tutors that teach courses– Course Administrators who manage the assignment

of courses to tutors– Calendars and Course Schedules that are generated

as a result of the work performed by the course administrators

– Students who refer to Calendars and Course Schedules to decide which courses they wish to take up for study

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Courseware Actors and Use Cases

• Actors: Tutor, Student, Course Administrator (main actor)

• Use Cases (primary business: secondary user)– Manage courses: View courses, Manage topics for a

course, and Manage course information– Manage tutors: View course calendar, View tutors,

Manage tutor information, and Assign courses to tutors

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Courseware Scenarios Example /1• Use Case: Manage Course Information (UC_ID1)

– Participating Actors: Course Administrator– Entry Conditions: Course Administrator is logged into

CourseWare– Exit Conditions: Course Administrator has received

an acknowledgement from the system that the selected transaction is complete, or if not complete, a message explaining the failure

– Quality Requirements: (Performance) Course Administrator receives a response from the system in less than 3 seconds

– Related Requirements: Create, Modify, and Delete Course

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Courseware Scenarios Example /2

• Use Case: Manage Course Information (UC_ID1)– Typical flow of events:

1. Course Administrator selects Create New Course a) System invokes Create New Course use case

2. Course Administrator selects Modify Existing Coursea) System invokes Modify Existing Course use case

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Courseware Scenarios Example /3• Use Case: Create New Course (UC_ID2)

– Participating Actors: Course Administrator– Extends: Manage Course Information (UC_ID1)– Entry Conditions: Course Administrator has selected

Create New Course option– Exit Conditions: Course Administrator has received an– acknowledgement from the system that a course has

been created, or if not, a message explaining the failure– Quality Requirements: (Performance) Course

Administrator receives a response from the system in less than 3 seconds

– Related Requirements: Create Course83

Courseware Scenarios Example /4• Use Case: Manage Course Information (UC_ID2)

– Typical flow of events:1.Course Administrator enters New Course Information

a) System invokes Validate Course Information use caseb) For a valid response, system creates a new course

entry and sends an acknowledgment back to the actor

– Exceptions:1. Course Administrator enters New Course Information

a) Invalid response received, so system reports failure with a message indicating invalid course information

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Courseware Scenarios Example /5• Use Case: Modify Existing Course (UC_ID3)

– Participating Actors: Course Administrator– Extends: Manage Course Information (UC_ID1)– Entry Conditions: Course Administrator has selected

Modify Existing Course option– Exit Conditions: Course Administrator has received an

acknowledgement from the system that a course has been modified, or if not, a message explaining the failure


– Related Requirements: Modify and Delete Course85


– Typical flow of events:1. Course Administrator selects Find Existing Course

option a) System searches for a selected course and

returns existing course information2. Course Administrator enters new course

information a) System invokes Validate Course Information

use caseb) For a valid response, system updates the

existing course entry and sends an acknowledgment back to the actor

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– Alternatives:1. Course Administrator selects Delete Existing Course

optiona) System invokes Delete Existing Course use case

– Exceptions:1. Course Administrator selects Find Existing Course option

a) System searches for a selected course and returns failure stating that the course could not be found

2. Course Administrator enters New Course Informationa) Invalid response received, so system reports failure

with a message indicating invalid course information

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Courseware Scenarios Example /8• Use Case: Delete Existing Course (UC_ID4)

– Participating Actors: Course Administrator– Extends: Modify Existing Course (UC_ID3)– Entry Conditions: Course Administrator has selected

Delete Existing Course option– Exit Conditions: Course Administrator has received an

acknowledgement from the system that a course has been deleted, or if not, a message explaining the failure


– Related Requirements: Delete Course 88

Courseware Scenarios Example /9• Use Case: Delete Existing Course (UC_ID4)

– Typical flow of events: a) System deletes a selected course and sends an

acknowledgment back to the user– Exceptions:

a) System cannot delete a selected course so it returns failure stating that the course could not be deleted

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One to Three

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