Transcript
UMLPrimera Herramienta
Casos de Uso
Roadmap• Use case and use case diagram• Break • Challenges and visions for software modeling
Steps Before CodingPhase Action Results
Initiation Raise a business need domain model, business use cases
Requirement What to accomplish(abstract)
use case, activity diagrams
Design How the system works(more details: software architecture, components, data types, algorithms)
component, class, sequence diagrams, formal specifications
Source of Requirements- Where they came from?
• Initial requirements come from the customer, by:1. Documents, such as RFI/RFP 2. Meetings, reports
• Advanced requirements come from the analysts, after studying scope and price 1. Feasibility (technological, organizational etc)2. Prototypes
• Final requirements are stabilized in an iterative process.
Types of RequirementsVisible Functional Requirements
“The system will deliver cash to the customer” “Cash will be delivered after card was taken out”
Qualitative Requirements “The authorization process will take no more than 1 sec” “The user interface will be easy to use”
Hidden Requirements “Database maintenance processes will occur every night”
Intro: Use Case and Use Case Diagram
Use Cases as Means of Communication
The use case should stimulate a discussion about what the system should do, mainly with people who are outside of the development team.
Customer Designer User
Use Case
A use case is a contract of an interaction between the system and an actor.
Use Case Diagram: an integration of use cases
Use Case DiagramA use case diagram illustrates a set of use cases for a system, the actors, and the interactions between actors and use cases.
A graphical overview of the functionality provided by a system in terms of actors, their goals (represented as use cases), and any dependencies between those use cases.
Use Case Diagram Objectives1. Create a semi-formal model of the functional
requirements
2. Analyze and define: • Scope • External interfaces • Scenarios and reactions
What makes a good Use Case Diagram?
Lack of ambiguity - Each requirement must be interpreted in a single manner.
Completeness - The collection of all use cases is everything that can be done to/with the system.
Consistency - Requirements should not conflict with each other. If there are, tradeoffs must be detected and discussed.
Avoid design- Requirements should raise a need, not answer it.
Construct a Use Case Diagram
Finding actors
External objects that produce/consume data:
1. Must serve as sources and destinations for data 2. Must be external to the system
Humans Machines External systems Sensors
Actor Relationships – Generalization/Specialization
Define hierarchy for actors
Notation
The child actor inherits all use-cases associations
Should be used if (and only if), the specific actor has more responsibility than the generalized one (i.e., associated with more use-cases)
Association: Actor and Use Case
Solid line:
Interaction between actors and use case
Arrowhead (optional)
• Control flow
• Initial invocation, primary actor
Use Case Levels
Use Case Relationships
• Goal: enable flexibility in requirements specification 1. Isolating functionality 2. Enabling functionality sharing 3. Breaking functionality into manageable chunks
• Relationships1. Include 2. Extend 3. Generalization
IncludeGoal: 1.Decomposing complicated behavior 2.Centralizing common behavior
the behavior of the included use case is inserted into the behavior of the including use case - The first use case often depends on the outcome of the included use case.
Extendthe behavior of the extension use case may be inserted in the extended use case under some conditions
Note the direction of the arrow The base use-case does not know which use-case extends it
Example: Amazon
Actors?
Base Use Cases?
Include?
Extend?
Generalization
use case may have common behaviors, requirements, constraints, and assumptions with a more general use case.
Example: Cellphone Company System
Hint - Actors: Phones, Phone Companies
Writing Use Cases
• Name: • Actors:• Descriptions: – Precondition– Main flow– Sub flow– Alternative flow
Precondition
• What the system needs to be true before running the use-case. – User account exists – User has enough money in her account – There is enough disk space
Main flowThe success scenario is the main story-line of the use-case • Assumption: everything is okay, no errors or problems occur, and it leads directly to the desired outcome of the use-case • It is composed of a sequence of subflows
Example:
Step 1: Administrator enters course name, code and description (interaction)Step 2: System validates course code Step 3: System adds the course to the db and shows a confirmation message (interaction)
Branches:
If the user has more than 10000$ in her account, the system presents a list of commercials Otherwise…
Repeats:
User enters the name of the item he wishes to buy System presents the items User selects items to buy Systems adds the item to the shopping cart User repeats steps 1-4 until indicating he is done
Sub flow
Used to describe exceptional functionality
Examples: 1. Errors 2. Unusual or rare cases 3. Failures 4. Starting points 5. Endpoints 6. Shortcuts
Alternative flows
Write Include in User CaseReference
Write Exclude in Use Case
Extension Point
Effective Use Cases
• Only one side (system or actor) is doing something in a single step
• Write from an “objective” point of view using active tense
• Any step should lead to some progress
Effective Use Cases
“Get the amount form the user and give him the money”
“User click the enter key”
ATM
1. No actor 2. Too many user interface details “User types ID
and password, clicks OK or hits Enter” 3. Very low goal details • User provides name• User provides address • User provides telephone number
Effective Use Cases – Common Mistakes
From Use-Case to Use-Case Diagrams
• Top down ? Starting with an overview of the system, and then
splitting Use-cases
• Bottom up ?Starting with throwing all scenarios on the page, and then combining them:
Most of the analysis process are actually combined
Common Rules
• Number Limit: The diagram should have between 3 to 10 base use-cases. No more than 15 use cases (base + included + extending). ---- If the dependency between two parts of a use-case is weak, they should be divided.
• Abstraction: All use-cases should be in similar abstraction levels.
• Size: Use cases should be described in half a page or more. - split using include/exclude
When we are done
• When every actor is specified. • When every functional requirement has a use-
case which satisfies it. • A tractability matrix can help us determine it:
Use Case and Use Case Diagram a Summary
When to useWhat is Use Case and Use Case DiagramHow to Construct Use Case DiagramHow to Write Use Case
Questions?
Traceability Matrix
• A traceability matrix is a document, usually in the form of a table, that correlates any two baselined
documents that require a many-to-many relationship to determine the completeness of the relationship. It is often used with high-level requirements (these often consist of marketing
requirements) and detailed requirements of the product to the matching parts of high-level
design, detailed design, test plan, and test cases.
Traceability Matrix
• A requirements traceability matrix may be used to check to see if the current project requirements are being met, and to help in the creation of a request for proposal, software requirements specification, various deliverable documents, and project plan tasks.
MATRIX EXAMPLE
Wild and Crazy Ideas Session
Extreme Programming (coding, testing, listening, and
designing)
vs. Product life cycle…….
top related