Requirement Analysis

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REQUIREMENT ANALYSIS

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Introduction• Requirements Gatherings

– Goals and Challenges– Standard Approaches– Example Requirements List– Documenting Operational Requirements

• Traditional Deliverables– Requirements Specification Documents– Analysis Diagrams:

• Context Diagram, • Entity Relationship Diagram, • Data/Control Flow Diagram

– Prototype

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Requirements Gathering

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Goals of Requirements Gathering• Find out what the users need• Document needs in a Requirements Specification

– Avoid premature design assumptions

– Resolve conflicting requirements

– Clarify ambiguous requirements

– Eliminate redundant requirements

– Discover incomplete or missing requirements

– Separate functional from nonfunctional requirements

• Ensure Requirements Traceability

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Requirement Specifications seldom clearly capture customer needs

What user wanted How customer described it How analyst specified it How designer implemented it

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Challenges in Requirements Gathering• Consider a scenario illustrating the normal state of flux:

Often you are using new business procedures, andyour job has changed to head development of a brand new application your company has announced, and you are scheduling training for you and your team to master a new computer environment and new software development techniques and new tools using a new programming language, how do you figure out and document how the new application is supposed to work in a way that is clearly understood by:

end users, analysts, training staff customers, designers,

support staff marketing staff,implementers, maintenance staff, managers, testers, . . . ?

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Standard Approaches for Requirements Gathering

• Elicit requirements through user interviews• Gathering representatives of stakeholders:

* executives developers maintenanceusers support staff ...

in one room at during uninterrupted session(s) to decide on requirements under an experienced leader/consensus maker:

Joint requirements planning (JRP)• focus on what the system will do

Joint application design (JAD) • focus on how the system will work

produce a document which includes a list of requirements

• Developing a Rapid Prototype

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Example Requirements List 1 (1 of 3)Table of Requirements with review comments by Kulak & Guiney1

1 Daryl Kulak and Eamonn Guiney. Use Cases: Requirements in Context, Addison-Wesley, New York, NY, 2000.

[KG00p16-18]

Requirement Kulak and Guiney Comments

The system will support client inquiries from 4 access points: in person, paper-based mail, voice communication, and electronic communication (Internet, dial-up, and LAN/WAN

Four access points are how; we should focus on who needs access and from where

The telephone system must be able to support an 800 number system

Can't use 888 or 877? Missing who needs what kind of access from where

The telephone system must be able to handle 97,000 calls/yr. and must allow for a 15% annual growth. It is estimated that 19% of these calls will be responded to in an automated manner and 81% will be routed to call center staff for response. 50% of calls can be processed without reference to the electronic copy of the paper file, and approximately 50% will require access to system files.

Valuable statistics. This requirement is actually pretty good.

For the calls that require access to system information, response times for the electronic files must be less than 20 seconds for the first image located on the optical disk, less than 3 seconds for electronic images on a server, and less than 1 second for data files.

"optical disk" is a design assumption. Response times are good non-functional requirements if not linked to design assumptions (hardware device types).

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Table of Requirements with review comments by Kulak & Guiney

[KG00p16-18]


The telephone system must be able to support voice recognition of menu selections, touch-tone menu selections, and default to a human operator. The telephone menu will sequence caller choices in order of most frequently requested information to the least requested

Pretty good one. Can you find anything wrong?

The telephone system must be able to provide a voice response menu going from a general menu to a secondary menu.

This seems to be trying to provide some pretty obvious advice to a dumb designer

The system must allow for the caller to provide address information through a digital recording and to indicate whether it is permanent.

"Through a digital recording"? This is a design assumption

The system must allow for the caller to provide address information through voice recognition and to indicate whether it is permanent.

Sound familiar? (It's redundant)

The telephone system must be able to store and maintain processor IDs and personal identification numbers to identify callers and to route calls properly to the appropriate internal response telephone.

Simplify it: "The system must be able to identify callers and route calls to the appropriate internal response telephone".

The telephone system must be able to inform callers of the anticipated wait time based on the number of calls, average duration of calls, and the number of calls ahead of them.

Great!

Example Requirements List 1 (2 of 3)

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Note: Each requirement should have a number to provide traceability.

[KG00p16-18]


The journal will contain entries for key events that have occurred within the administration of an individual's account. The system will capture date, processor ID, and key event description. The system will store pointers to images that are associated with a journal entry as well as key data system screens that contain more information regarding the entry.

This is a design for a journal. Why have it? What is its purpose?

If an individual double-clicks on an event in a member's journal, the system will display the electronic information and the images associated with the event.

Double-click is a user interface design assumption

The system will restrict options on the information bar by processor function. When an icon is clicked, the screen represented by the icon will be displayed and the system will display appropriate participant information.

This one has many user interface design assumptions.


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[KG00p3-7]


6.7.1.2 The system must provide the capability to capture all of the customer transactions for fiscal year

Too vague. Implies fiscal year has some impact on how customer transactions are organized, but does not specify what that is. Implies some data entry, but needs to be stated more specifically. May be trying to make a statement about volume, meaning old transactions can't be archived until they are a year old?

6.7.1.3 The system will provide restricted remote inquiry access (via dial-in) to view images and data separately or simultaneously

Saying "restricted" is OK, but details about the restriction (who can, who can't) should be stated clearly in this context. Also vague is the reference to remote inquiry. How remote? Saying "remote access" when referring to mobile employees working in the field but still within a couple of miles of the office or worldwide access. Can have huge implications on system.

6.7.1.4 The system will barcode documents automatically prior to distribution. At a minimum, the codes will be used to identify to which work queue the documents should be routed within the organization when they are returned

Makes several technical design assumptions. Barcoding is a solution, not a requirement. This system probably needs a way to identify each document uniquely, but it doesn't have to be barcodes. If all existing systems use document barcoding (not the case with this system), should write a nonfunctional requirements that states, "Unique identification of all documents will be done through barcoding". By specifying barcoding in the functional specifications, changing to glyphs, optical character recognition (OCR) will be more difficult. The reference to queues makes an assumption about a workflow-package-oriented system. Better to state: "At a minimum, the unique id will ensure routing to a specific worker in the organization when documents are returned."


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[KG00p3-7]


6.7.1.5 When a workflow is initiated, the system must be able to prefetch the documents that are in electronic image format by document type or grouping of documents by process

Look at references to workflow. Requirements document has specified a workflow solution! This whole entry is suspicious. Seems to be saying that we must cache documents by two different criteria: by type or by process. Criteria are good requirements, but caching(prefetching) is a solution to address performance problems.

6.7.1.6 The system must create an entry in the journal file whenever a letter is created

Assumes presence of a journal file containing entries inserted when a letter is created. Seems focused on front end ("do this") instead of back end ("in order to get this"). Why put entries in a journal file? To create a list of all letters created, when and by whom? This would make a better, clearer requirement.

6.7.1.7 System must maintain list of current, open work processes and identify work process to be executed and workflow queue for process. When documents are scanned, system determines whether there is a process open for that SSN. If there is, the system routes document to appropriate workflow queue, displays work process script, and highlight current work process.

Seems to be focused on how rather than what. Instead of specifying the steps a system must go through, clearly document the end in mind. Example: "When a new document image is brought into the system, it should be routed to the worker who has the account open for the same SSN as the new document and should be made obvious to that worker. If no worker has an open account, the document should be made available to any worker."


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Eliciting Operational Requirements

Problems with traditional ways of specifying problems:

1. customer may not adequately convey the needs of the user.

2. developer may not be an expert in the application domain, which inhibits communications.

3. users and customers may not understand the requirements produced by the developer

4. developer's requirements specifications typically specifies system attributes such as • functions, • performance factors, • design constraints, • system interfaces and

• quality attributes, but typically contains little or no information concerning operational characteristics of the specified system.

[FT97] R. E. Fairley and R. H. Thayer, "The Concept of Operations: The Bridge from Operational Requirements to Technical Specifications," Software Engineering, M. Dorfman and R. H. Thayer (eds.), IEEE Computer Society Press, Los Alamitos, CA, 1997.

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Guidelines for Operational Concept Document

Operational Concept Document (OCD) describes the mission of the system, its operational and support environments, and the functions and characteristics of the computer system within an overall system. Several guidelines and standards exist to prepare an OCD:• Mil-Std 498 for Department of Defense SW

development• IEEE Standard 1498 for commercial SW development,• AIAA OCD 1992 for the American Inst. of

Aeronautics and Astronautics (for embedded real-time systems)• ConOps 1997 Concept of Operations Document

Guidelines proposed by Fairley and Thayer [FT97] because they felt the

above guidelines were systems-oriented and developer-oriented instead

of user-oriented.

[FT97] R. E. Fairley and R. H. Thayer, "The Concept of Operations: The Bridge from Operational Requirements to Technical Specifications," Software Engineering, M. Dorfman and R. H. Thayer (eds.), IEEE Computer Society Press, Los Alamitos, CA, 1997.

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The Concept of Operations Document

Identifies •classes of users and •modes of operation

•normal mode •emergency mode•maintenance mode•backup mode•degraded mode •diagnostic mode

Users communicate•essential needs•desirable needs -- prioritized•optional needs -- prioritized

Prioritized user needs provide the basis for •establishing an incremental development

process, and •making trade-offs among operational needs, schedule and budget.

[FT97]

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Concept Analysis Team, include representatives from• user organization • training• buyer organization • operational support• developer organization or development

experts/consultants

Results of concept analysis are recorded in the ConOps document written in narrative prose using users' language, and using visual forms (diagrams, illustrations, graphs, etc.) wherever possible.

Each operational scenario needs a test scenario to validate the system in user's environment. Validate proposed system by walking thru all scenarios, include both normal and abnormal operations: • exception handling, • stress load handling, • handling incomplete data,• handling incorrect

data.

Concept Analysis

[FT97]

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5 Concepts of Operations for the New or Modified Proposed System 5.1 Background, Objectives & Scope5.2 Operational Policies & Constraints5.3 Description of Proposed System5.4 Modes of Operation5.5 User Classes

5.5.1 Organization Structures5.5.2 Profiles of User Classes5.5.3 Interactions among User Classes

5.6 Other Involved Personnel5.7 Support Environment

6 Proposed Operational Scenarios

7 Summary of Impacts7.1 Operational Impacts7.2 Organizational Impacts7.3 Impacts During Developments

8 Analysis of Proposed System8.1 Summary of Improvements8.2 Disadvantages & Limitations8.3 Alternatives/Tradeoffs considered

9 Notes, Appendices, and Glossary

1 Scope1.1 Identification1.2 System Overview1.3 Document Overview

2 Referenced Documents3 The Current System or

Situation3.1 Background, Objectives, & Scope3.2 Operational Policies & Constraints3.3 Description3.4 Modes of Operation3.5 User Classes

3.5.1 Organizational Structure3.5.2 Profiles of User Classes3.5.3 Interactions3.5.4 Other Involved Personnel

3.6 Support Environment4 Justification for and Nature of Proposed

Changes & New Features4.1 Justification4.2 Description4.3 Priorities among Changes/ Features4.4 Changes/Features Considered but

Not Included4.5 Assumptions and Constraints

Outline for a Concept of Operations Document

[FT97]

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Rapid Prototype

[www.dilbert.com ]

Having a prototype during requirements phase gives you something to work from when communicating with the users and client, and results in a user-centered GUI design

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Traditional Expressions of Functional Requirements

• Requirements specifications– Hard to read. Contract-like.

• Context Diagram– Specifies users, software, hardware that interface with system

• Data-flow Diagrams (DFD)– Useful for technical people but tend to confuse users– Useful in design of non-object-oriented systems

• Entity-relationship diagrams (ERD)– Critical to database design but are not easily understood by users

• Prototypes– Good communication tool to elicit information from user. – Great for proof-of-concept tasks. – Useful in developing user interface designs.

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Unified Modeling Language (UML)

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UML Diagrams• Instead of the Context, Data-Flow and Entity-

Relationship Diagrams used in Structured Analysis, UML produces 9 types of diagrams– Use Case Diagram– Sequence Diagram– Collaboration Diagram– Statechart Diagram– Activity Diagram– Class Diagram– Object Diagram– Component Diagram– Deployment Diagram

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Use Cases

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History of Use Cases• Ivar Jacobson and his team at Ericsson in

Sweden introduced Use Cases in their book:I. Jacobson, M. Christerson, P. Jonsson, and G. Overgaard. Object-Oriented Software Engineering: A Use Case Driven Approach, ACM Press, 1992.

• Use Cases were included as part of their overall system development lifecycle methodology, called Objectory, which was sold to Rational Software. Now Use Cases are part of the Rational Unified Process, created by the "three amigos":

I. Jacobson, G. Booch and J. Rumbaugh. The Unified Software Development Process, Addison-Wesley, 1999.

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What is a Use Case?• The Use Cases describe the behavior of a system

from a user's standpoint using actions and reactions.• The Use Case Diagram defines the system's

boundary, and the relationships between the system and the environment:– different human users roles interact with our system– other software systems/applications– hardware systems/devices

• Use Cases support the specification phase by providing a means of capturing and documenting requirements

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Use Case Deliverables• There are two parts to document a use case:

– the use case diagram, • provides visual overview of important interactions

• captures scope (identifies external entities)

– the use case itself• documents in a textual form the details of the

requirements, what the use case must do.

• A use case is actually a page or two of text representing each oval in the use case diagram

• A project should have a standard template for use cases.

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Use Case Diagram

Buyer

Advisor

Seller

Sell Property

Real Estate System

actor

interaction

use case

system

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Use Case Documentation TemplateUse Case Number: A unique numeric identifier Use Case Name: A unique descriptive identifier

Iteration: Facade (Outline and high-level description), Filled (Broader, deeper), Focused (Narrower, pruned), Finished

Summary: Briefly state the purpose of the use case in one or two sentences to provide a high-level definition of the functionality provided by the use case.

Basic Course of Events: 4. Include the following:

4.1 What interaction the use case has with the actors

4.2 What data is needed by the use case 4.3 When and how the use case starts and ends 4.4 The normal sequence of events for the use case 4.5 The description of alternate or exceptional flows, what happens if ... 5. The description of each step grows in detail as analysis

progresses

1. This is a numbered list. The use case number is used togetherfor with this number to provide requirements traceability

2. Write this as a flow of events describin what the system should do, not how the system should do it.

3. Write it in the language of the domain, not technical jargon

Alternative Paths: What happens if ... invalid information is entered, unusual types of processing occurs, or uncommon conditions occur, how is the flow completed?

Exception Paths: What happens if... an error occurs, how is the flow affected?

Extension Points: Describes an <<extend>> relationship, shows steps which are extended by optional steps in another case

Trigger: Describe entry criteria for use case, may describe business need, may be time-related, or completion of other case

Assumptions: Critical section for project manager. Things (out of scope of system) you assume to be true but might not be true

Preconditions: List things that must be in place before interaction can occur. (Part of contract between use case & outside world.

Postconditions: List things that will be satisfied if use case is completed successfully. Independent of alternative paths taken.

Related Business Rules: Written and unwritten company business rules that relate to requirements presented in this use case

Author: This is placed at the bottom, together with the date to allow critical information to be speed read

Date: Facade, Filled, Focused, Finished dates [KG0042]

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Use Case Documentation ExampleUse Case Number: 1 Use Case Name: Sell Property

Iteration: Filled (Four stages of iteration are Facade, Filled, Focused, and Finished)

Summary: System Context Use Case. The seller lists the property, a buyer purchases the property, and the agent guides them through the process and offers advice, caution, and recommendations

Basic Course of Events: 9. System responds by notifying seller and seller's agent10. Seller responds to the offer with a counteroffer.11. System responds by notifying buyer and buyer's agent.12. Buyer and seller agree to terms13. System responds by recording the agreement14. Buyer indicates a loan is required15. System responds by locating an appropriate loan provider16. Buyer and loan provider agree to loan terms.17. System responds by recording terms of loan18. Buyer and seller close on property.19. System responds by recording details of close.

1. Seller selects an agent2. System responds by assigning an agent and notifying the

seller's agent.3. Seller lists the property to sell.4. System responds by displaying this property in the property

listing and linking it for searches5. Buyer selects an agent.6. Buyer reviews the property listings by entering search criteria7. System displays properties matching buyer's search criteria8. Buyer finds a property and makes an offer on it.

Alternative Paths: N/A

Exception Paths: N/A

Extension Points: N/A

Trigger: N/A

Assumptions: N/A

Preconditions: N/A

Postconditions: N/A

Related Business Rules: N/A

Author: Rumpel Stilskin

Date: March 10, 2001 – Facade; April 20, 2001 -- Filled

[KG00p25-26]

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A Simpler Use Case Template• A simpler template for Use Case documentation is

recommended by Terry Quatrani [TQ98]• For each use case:

X Flow of Events for the <name> Use Case

X.1 Preconditions

X.2 Main Flow

X.3 Subflows (if applicable)

X.4 Alternative Flowswhere X is a number from 1 to the number of the use case

[TQ98] Terry Quatrani. Visual Modeling with Rational Rose and UML, Addison-Wesley, Reading, Mass., 1998.

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Associations in Use Case Diagram• Associations can exist

– between an actor and a use case, – between use cases, and – between actors

• Types of Use Case Associations– Communicates between actor and use case

• named or unnamed relationship showing participation of actor in use case, use a solid line connecting actor to use case

– Generalization between actors– Adornments = Stereotyped Associations between use cases

• <<extend>> indicates relationship between use cases in which a special use case (the non-arrow end) extends an original use case (the arrow end)

• <<include>>reuses steps in a use case instead of cut-and-pasting steps into multiple use case documents, by pulling out common steps into a new use case and specifying with an arrowed line the <<include>> association between this new use case and those use cases requiring the steps

• <<uses>>An instance of the source use case includes behavior described by the targetShows a stereotyped generalization relationship between use cases

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Example of Generalization between Use Case Actors

Service Representative

Customer Service Representative Field Service Representative

[KG00p40]

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Example of Communicates Use Case Relationship

Buyer

Sell Property

Buyer

Sell PropertyTriggers

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Example <<uses>> and <<extends>> Use Case Relationships

Remote Customer

Transfer by computer

Transfer

<<extends>>Local Customer

Identification

<<uses>>

[PM97p97][PM97] Pierre-Alain Muller. Instant UML, Wrox Press, Birmingham, UK.

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Office Administrator

Schedule Customer Appointment

<<extends>><<includes>>

Example <<include>> and <<extends>> Use Case Relationships

Schedule Recurring Customer AppointmentSchedule Designer

Enter Customer Order

<<includes>>

[KG00p41]

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Course Registration ExerciseProblem Statement:

At the beginning of each semester, students may request a course catalog containing a list of course offerings needed for the semester. Information about each course, such as professor, department and prerequisites are included to help students make informed decisions.The new system will allow students to select four course offerings for the coming semester. In addition, each student will indicate two alternative choices in case a course offering becomes filled or canceled. No course offering will have more than ten students or fewer than three students. A course offering with fewer than three students will be canceled. Once the registration process is completed for a student, the registration system sends information to the billing system so the student can be billed for the semester.Professors must be able to access the online system to indicate which courses they will be teaching, and to see which students signed up for their course offerings.For each semester, there is a period of time that students can change their schedule. Students must be able to access the system during this time to add or drop courses.

Exercise: Create a Use Case Diagram and Use Case Documentation.

[TQ98p17]

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Introduction to Rational Rose

Rational Rose 2000 (v6.5)

1 month trial version needs key

www.rational.com

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Diagram window

Diagram toolbar (unique to each type of diagram)Browser window

(used to organize and navigate)

Documentation window

Standard toolbarStandard menu

Rat

ion

al R

ose

En

viro

nm

ent

Status bar

Can be hidden, docked or floating

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The View Menu• Allows you to control the desk top arrangement by

hiding, or displaying:– The Browser Window– The Documentation Window– The Status Bar– The Standard Toolbar– The Diagram Toolbox

• Right clicking on one of the above items (on one of the components in them) allow the item to be– Docked– Floating– Hidden

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The Toolbars• Right Clicking on a Toolbar/Toolbox button

allows you to:– Dock the Toolbar– Float the Toolbar– Use Large Buttons– Customize

• If the Toolbar/Toolbox is not visible, select it using the View Toolbars menu

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The Tools Menu• Under the Tools menu item, can:

– Generate Code in • Ada• Java• Oracle8• C++• XML_DTD

– Reverse Engineer Models from Code– Add Version Control– ...

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The Browser Window• Used to navigate through the

models and documentation using an textual outline• Expand and contract using

or in front of the View• Select model/component

• Browser may be made visible or hidden by• using the View menu, or• right-clicking on an item in the

Browser window.• Browser may be docked or

floating by • right-clicking on one of the

items in the Browser window.

Views from theBrowser window

+-

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4+1 View of Software Architecture• Software architecture consists of 5 concurrent views [PK94]

• Rational Rose provides 5 different perspectives/views.• Selecting a view allows users to focus only on what is

architectural significant and meaningful to themView Target Audience:

Use-Case View End UserLogical View Analyst/DesignerProcess View System IntegratorDeployment View System EngineerImplementation View Programmer

[PK 94] Philippe Kruchten. Software Architecture and Iterative Development. Rational Software Corporation,Santa Clara, CA, April 1994.

in Rose: Component View

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4 Views + 1 Architectural View

[RR00]

in Rose: Component View

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The Use-Case View• From end-users' perspective• Concerned with

– Understandability– Communication– Usability

• Use Case Modelcaptures system's intended functions and interactions with environment

– use case diagrams– use case flow of events– supplemental documentation– activity diagrams (optional)

• requirements specification.Use Case Model can serve as a contract between customer and developer instead of the traditional text requirement specification

A Use Case Diagram [RR00]

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The Logical View• Concerned with

functional requirements of the systems

• From analyst/designer perspective

• Includes • use case realization diagrams • class diagrams• interaction diagrams• statechart diagrams (optional)• activity diagrams (optional)

A Class Diagram [RR00]

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The Process View• Presents a perspective for the System Integrators• Non-functional requirements

Include:– Performance– Scalability– Availability– Fault Tolerance– Throughput– Concurrency and synchronization

• threads• processesNote: Not necessarily a single processing environment

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The Deployment View• For System Engineers• Used only for distributed systems• Captures how executables and other run-time

components are to be mapped to platforms or computer nodes

• Includes:– Performance – Delivery– Scalability – Installation– Availability – Fault Tolerance– Deployment Diagram

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The Implementation View• Called Component View in Rational Rose• Aimed at Programmers• Captures organization of static software modules:

– packaging, layering, and configuration management• source code files• data files• components• executable, etc.

• Concerned with derived requirements:– ease of development– software management– reuse– constraints imposed by programming language and development tools– sub-contracting– off-the-shelf components

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The Documentation Window

• Used to create, view and modify text documenting a selected item.

• May be visible or hidden; docked or floating– can be changed

• by selecting using View menu or • right clicking on an item in the Documentation Window

• The information added to the documentation window automatically updates the Documentation field in the appropriate specification.

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The Diagram Window• Allows you to create, update, and modify

graphical views of the current model.

• The Diagram Toolbox is unique to the diagram type, and changes automatically when you change types of diagrams.

• Select a diagram or add a diagram by selecting it from those listed under the appropriate view in the Browser Window

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The Specification Window• Textual

representation of a model element that permits viewing and manipulating the element's model properties

• Open by right clicking on a View in the Browser Window

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The Log Window• Reports

– progress– results– errors

• Right click in the Log Window to set available action

• Ctrl-tab from Log Windows returns to previous diagram

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Creating the 4+1 Views

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The Rational Unified Process

Inception

Elaboration

Construction

Transition

1 2 3 ...

Inception Phase: • establish business rationale for project• decide project scope • get go-ahead from project sponsor

Elaboration Phase: • collect more detailed requirements • do high-level analysis and design• establish baseline architecture• create construction plan

Construction Phase: • build, test and validate the project

Transition Phase: • beta-test• tune performance • train users

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Developing the Use Case View• In the Inception Phase

– Identify actors – Identify principal use cases

• In the Elaboration Phase– More detailed information is added

• associations

• stereotypes

– Additional use cases are added as needed

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Finding Actors• Actors are NOT part of the system.• Actors represent anyone or anything that interacts with

(input to or receive output from) the system• Questions to help find actors [TQ98p21-22]

– Who is interested in a certain requirement?– Where is the system used within the organization?– Who will benefit from the use of the system?– Who will supply the system with information, use this information, and

remove this information?– Who will support and maintain the system?– Does the system use an external resource?– Does one person play several different roles?– Do several people play the same role?– Does the system interact with a legacy system?

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Creating Actors in Rational Rose1. Right-click on the Use Case View package in the

browser to make the shortcut menu visible.

2. Select the NewActor menu option. A new actor called New Class will appear in the browser under Use Case View

3. The New Class actor to the desired name

4. Move cursor to the Documentation Window and add the documentation.

5. Repeat until all actors are added and documented

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Finding Use Cases• Use case = a sequence of transactions performed by a system that

yields a measurable result of values for a particular actor

• The use cases = all the ways the system may be used.• Questions to help find use cases [TQ98p25]

– What are the tasks of each actor?– Will any actor create, store, change, remove or read information in the

system?– What use cases will create, store, change, remove, or read this information?– Will any actor need to inform the system about sudden, external changes?– Does any actor need to be informed about certain occurrences in the system?– What use cases will support or maintain the system?– Can all functional requirements be performed by the use cases?

59

Creating Use Cases in Rational Rose

1. Right-click on the Use Case View in the Browser to make shortcut menu visible.

2. Select the NewUse Case menu option.

3. With the unnamed use case selected, enter the desired name.

4. Move cursor to documentation window and add a brief description.

5. Repeat for each use case.

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Finding Flow of Events• Flow of events document is typically created in the

elaboration phase• Each use case is documented with flow of events

– a description of events needed to accomplish required behavior– written in terms of what the system should do, NOT how it should do it– written in the domain language, not in terms of the implementation

• Flow of events should include– When and how the use case starts and ends– What interaction the use case has with the actors– What data is needed by the use case– The normal sequence of events for the use case– The description of any alternate or exceptional flows

• Each project should use a standard template.– See the previous slides in the requirements section for two suggested

templates used to document in detail each requirement.

61

The Use Case View for the

Case Study:Course Registration System

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The Actors• In the Course Registration System, answering the

questions suggested to find actors yields:– Students want to register for courses– Professors want to select courses to teach– Registrar must create the curriculum and generate a catalog for the

semester– Registrar must maintain all the information about courses, professors,

and students– Billing System must receive billing information from the system

• Actors identified from above:– Student – person registered/registering in classes at the University – Professor – person certified to teach classes at the University– Registrar – person who maintains the Course Registration System– Billing System – external software system that does student billing

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Add Actors to System

[TQ98p24-25]

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The Use Cases• Answering the questions to find use cases yields:

– The Student actor needs to use the system to register for courses– After the course selection process is completed, the Billing System must be

supplied with billing information– The Professor actor needs to use the system to select the courses to teach for a

semester, and must be able to receive a course roster from the system– The registrar is responsible for the generation of the course catalog for a

semester, and for the maintenance of all information about the curriculum, the students, and the professors needed by the system

• Based on the needs, the following cases are identified:1. Register for courses2. Select courses to teach3. Request course roster4. Maintain course information5. Maintain professor information6. Maintain student information7. Create course catalog

[TQ98p24-25]

65

Add Use Cases to the SystemGive a brief description of

each use case i the Documentation window

This is the summary description for

Register for courses

[TQ98p28-29]

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The Flow of Events• Exercise: Form a team and agree on a standard template

to use for documenting flow of events for the use cases.– Look at Quatrani's recommended template [TQ98] and

• The following flow of event for the Select Courses to Teach use case follows Quatrani's recommended template [TQ98]

• For each use case:X Flow of Events for the <name> Use CaseX.1 PreconditionsX.2 Main FlowX.3 Subflows (if applicable)X.4 Alternative Flows

where X is a number from 1 to the number of the use case

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The Flow of Events (1 of 4)

[TQ98p30]

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[TQ98p31]

69


[TQ98p31-2]

70


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Use Case Diagram (1 of 2)

[TQ98p38]

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Use Case Diagram (2 of 2)

[TQ98p31]

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Exercises• Individually create a Problem Statement and Use Case Diagram for

one of the following Vending Machines:1. Hot Drink Vending Machine that mixes and dispenses two sizes of hot drinks

(coffee, tea, hot chocolate) with/without cream and sugar/sweetener. 2. Ice Cream Vending Machine that dispenses prepackaged ice cream (individual

cups, bars, cones, sandwiches – pre-wrapped)3. Carousel Vending Machine that dispenses a variety of food (many with

expiration date) on a stack of see-thru carousels containing a number of individual food compartments. Each carousel has a door. The customer turns the carousels until the item is positioned in front of a door.. The action of sliding open the door, selects and dispenses the food.

• Meet in a team of 3-4, discuss each Problem Statement and Use Case Diagram, features (such as sensors, credit cards payment) that would enhance the marketing of the product. Produce a group Problem Statement and Use Case Diagram. – Turn in all the statements/diagrams with the author's name, clearly mark the

group approved ones with all the team members' names and initials. Select one team member and an alternate that will walkthrough the statement and diagram for the class to review.

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The Logical View

Develop Class Diagrams

Develop Interaction Diagrams

Develop State Diagrams

Develop Activity Diagrams

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Developing the Logical View• One of the main diagram produced in the logical view is the

Class Diagram.• The Rational Unified Process suggests using a model-view-

controller perspective to partition the system by separating the view from the domain from the control needed by the system.

• Typical Class Stereotypes:– Entity Classes (or Domain Classes)

• may reflect real-world entity or may perform tasks internal to the system. • may be used in multiple applications; are surrounding independent

– Boundary Classes • model system interfaces between the actors and the application• are surrounding dependent

– Control Classes• coordinate events needed to realize one or more use cases• typically are application-dependent

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Top-Down or Buttom-Up?• Top-Down – Identify Packages first, then Classes

– Right click on Logical View in the Browser, select NewPackage, or drag-drop toolbox icon into the Class Diagram, name the package and fill documentation. More details are added using Specification Window.

– To insert new classes into the package: Right click on the package in the Browser, and select NewClass, name the class and fill documentation description

– To insert existing classes into the package: In the Logical View in the Browser, click on class and drag into package.

• Buttom-Up – Identify classes first, then group– Right click on Logical View in the Browser, select NewClass, name the

class and fill documentation. Repeat until most classes are identified.

– Organize classes into groups by creating packages

– Insert the classes into the appropriate package: In the Logical View in the Browser, click on class and drag into package

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Select a Use Case and SubFlow• Look at a use case: Select Courses to Teach• Select a subflow: Add a Course Offering• Although the flow is written sequentially, in the real world many steps

may occur concurrentlyThe professor logs onto the Registration System and enters password. The system verifies the password is valid (E1) and prompts the professor to select the current semester or a future semester (E2). The professor enters the desired semester. The system prompts the professor to select the desired activity: ADD, DELETE, REVIEW, PRINT, or QUIT. The professor chooses ADD, the S-1: Add a Course Offering subflow is selected. S-1 Add a Course OfferingThe system displays the course screen containing a field for a course name and number. The professor enters the name and number of a course (E-3). The system displays the course offerings for the entered course (E-4). The professor selects a course offering. The system links the professor to the selected course offering (E-5). The use case then begins again.E-3: An invalid course name/number is entered. The user can re-enter a valid name/number combination or terminate the use caseE-4: Course offerings cannot be displayed. The user is informed that this option is not available at the current time. The use case begins again.E-5: A link between the professor and the course offering cannot be created. The information is saved and the system will create the link at a later time. The use case continues

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What is a Scenario?• What is a scenario?

– A use case is a class, not an instance; it describes the functionality as a whole and includes possible alternatives, exceptions and errors that are possible during the execution of the use case.

– A scenario is an instantiation of a use case or a collaboration. It represents an actual usage of the system -- a specific execution path through the flow of events.

Example from [EP98]:

Use Case: Signing Insurance

Scenario: "John Doe contacts the system by telephone and signs for car insurance for his new Toyota Corolla"

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Scenarios• Scenarios are used to complement (not replace) and

clarify a use case description in terms a user can understand

• A set of scenarios are used to illustrate the use case or collaboration. Make sure to select scenarios that illustrate normal and abnormal (using exceptions and alternate flows). – When a scenario is viewed as a use case, describe only the

external behavior toward the actors– When a scenario is viewed as an instance of a collaboration,

describe the internal implementation of the involved classes, their operations and communications

• A scenario is presented as a numbered sequence of steps.

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Relationship between Use Case, Collaboration, and Scenario

Scenario

[EP98p61]

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[EP98p63]

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Identify Classes and Create Packages

Identify Boundary Classes

Identify Entity Classes

Identify Control Classes

Create Packages

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Identify Boundary Classes• Identify Boundary Classes

– With what actors does the use case interact? Professor

• What information do we need to keep track of?– what options is the professor allowed to use

» add, modify, delete, review, print course offering

ProfessorCourseOptions• What information do we

– Class to take care of use case subflow:AddACourseOffering

• What general flows do we need to support?

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Identify Entity Classes• Domain Classes identified:

– Course– CourseOffering– ProfessorInformation keeps track of

professor's course assignment

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Identify Control Classes• Add control classes to handle the flow of

events for the use case:– ProfessorCourseManager

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Create Packages• Classes identified:

– Boundary Classes

ProfessorCourseOptions

AddACourseOffering

– Entity ClassesCourse

CourseOffering

ProfessorInformation

– Control ClassesProfessorCourseManager

• Group classes into packages:Three Logical Groups:

Interfaces

UniversityArtifacts

People

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References• References used:

[EP ] Hans-Erik Eriksson and Magnus Penker. UML Toolkit, John Wiley & Sons, New York, NY, 1998. ISBN 0-471-19161-2

[MF97] Martin Fowler with Kendall Scott. UML Distilled: Applying the Standard Object Modeling Language, Addison-Wesley, Reading, Mass, 1997. ISBN 0-201-32563-2

[KG00] Daryl Kulak and Eamonn Guiney. Use Cases: Requirements in Context, Addison-Wesley, New York, NY, 2000. ISBN 0-201-65767-8

[PK 94] Philippe Kruchten. Software Architecture and Iterative Development. Rational Software Corporation, Santa Clara, CA, April 1994.

[PM97] Pierre-Alain Mueller. Instant UML, WROX Press, Chicago, IL[TQ98] Terry Quatrani. Visual Modeling with Rational Rose and UML, Addison-Wesley,

Birmingham, UK, 1998. ISBN 1-861000-87-1

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Useful URLshttp://members.aol.com/acockburn -- Alistair Cockburn's papers on use cases

Requirement Analysis

Documents

Transcript of Requirement Analysis