What are Requirements? Functional requirements describe a list of functions that the system must...
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What are Requirements?
• Functional requirements describe a list of functions that the system must accomplish.
• Nonfunctional requirements describe other constraints such as performance expectations or standards to be used.
• This discussion centers around functional requirements. Knowing what is to be built is one of the most important aspects of a software development process.
• Getting the requirements in line with what the actual users need is also a very important aspect.
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Use Cases
• Requirements are often based on use cases. • A use case can be used to describe a systems functional
requirements.• A use case treats the system which is to be built as a
black box. A user (Actor) does something and the system responds.
• The use case is not described in terms of GUI components or specific systems. Instead it is described in more generic terms as simple user actions.
• For example, entering data, viewing the results of a query to the database, etc..
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How can Requirements be Described?
• SRS– The IEEE and many government agencies
describe requirements through the use of Software Requirements Specifications (SRS). Each has a definition for the required contents.
• Use Cases– Requirements can be described as use
cases.
• The two traditionally haven’t been related.
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Use Cases and RequirementsExample
• Actor:Auctioneer• UseCase:EnterBidInformation
– Requirement:InputPersonThe system shall allow the Auctioneer to enter the
contents of the city, name, useCreditCard associated with the Person
– Requirement:ProcessCreditCard The system shall allow the Auctioneer to run the
VerifyWithBank algorithm described as: Go out to the Bank server, process the credit card transaction
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How can Requirements be Described? Cont’d
• Simulation– A mechanism which can be used to communicate the
requirements as use cases.– The simulation shows how the user interacts with the
system and how the system responds.
• Modeling– UML tools such as Together™ enable you to create
requirements by creating use cases. They provide diagrams to chose from which you can drag and drop.
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RequireMentor™ Tool
• Guides you to describe use cases for a system which you are specifying– you pick and choose forms and fill in blanks
• Creates simulations of use cases• Relates requirements and use cases• Creates SRS• Creates a model
class diagrams sequence, activity, use cases
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1. Define Actors
• Start by creating Actors and Job Titles
• Create separate types of Actors.
• They are distinguished by the Jobs that they do using the computer.
• Each Actor belongs to an organization
• Create all your known Actors and assign only the ‘Jobs’ for now. Job’s are optional.
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Actors and Job Titles
• Attempting to answer the question:
• Who will be using the system and what types of activites do their jobs include?
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2. Create Roles
• For each Actor, define one or more Roles.
• Roles are distinct interactions that an Actor has with the computer to accomplish a meaningful unit of work
• Later, you will define a Use Case for each role.
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3.Create Use Cases
• Create Use Cases for each Actor, one for each of its Roles.
• For now, just fill out the Use Case name, select an Actor, and select one of its Roles.
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4. Define a Story for each use case
• A Story is a sequence of screens which simulate how the Actor will interact with the system.
• A Story has an initial Screen.• Each Screen is associated with a
Requirement in the form:– The system shall …
• Choose from a fixed collection of Screen types
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Five Screen Types
• Input Data
• View Data
• View and Select from Data
• Input from a Device
• Run Processing
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5. Enter Info for the Screen Type
• Enter the Screen name
• Select a previously defined Data Entity (or define one on the fly
• Do not link Screen into a sequence by filling out Select Next screen at this time.
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6. Define a Data Entity
• A Data Entity is named and has a collection of fields
• Each field has a type
• The type may be another Data Entity
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Add Additional Screens
• Create another Screen for each of the Requirements within the Story
• The initial screen must be so designated
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4. Link Screens Together
• Link a screen to another Screen defined for the story or to another story
• If you like to another Story, you can reuse it.
• For example, may want to always verify the user’s name and password from several different places.
• Link the Password Story as a next screen
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6. View the Documentation
• As an Software Requirements Spec
• As a running simulation in html
• As an XMI(eye) file which can be imported into a UML tool
• Can also export the project as XML(el) or just save it
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Together™ Import XMI
• Open Together 6.0
• Create a new Project using the Project Wizard
• Select File->Import->Model from XMI
• Class, Use Case, Sequence, and Activity Diagrams will be created
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Guided Generation of Software Requirements
• RequireMentor™ was used to discover classes and methods
• Together™ was used to create the UML models
• RequireMentor™ provided guidance for– defining the contents of a use case– defining the format of requirements– generating many descriptions of the
requirements