![]() The system must support users on the move. Combining generalizations of actors and use-cases can be dangerous Bad: Undergrad can submit thesis Good: Only graduate student can submit thesis Introduction | Diagrams | Writing | GuidelinesĮxample: Phone Company Operational System Orange’s objective: Build a system that handles SMS messages, handles calls (for 2 and 3 generation phones), including conference calls and multiple calls from a single phone.Overriding occurs through the textual description Example Introduction | Diagrams | Writing | Guidelines.Child use-case can substitute parent Use case.Use case links (associations, include, extend, generalization).The interaction (described in the textual description).The child use case inherits the behavior parent use case:.The base use-case does not know which use-case extends it Example > Product is a gift Perform Sale After checkout Introduction | Diagrams | Writing | GuidelinesĮxample: Amazon Shopping Cart Product Page Review Writing Introduction | Diagrams | Writing | GuidelinesĮxample – cont’d Rank Supplier «extend» Search Product View Product Details «include» Write Review After page generation «extend» Navigate Deals «include» Add to cart «extend» Checkout «include» «extend» user is not a member Login Register Handle Order Status «include» Introduction | Diagrams | Writing | Guidelines.The base use case can incorporate another use case at certain points, called extension points.Gift wrap Products Extend – Graphical Representation Example > Introduction | Diagrams | Writing | Guidelines The base use case explicitly incorporates the behavior of another use case at a location specified in the base.Perform Sale Fill-in billing info The “Include” Construct Use-Case Levels Base Use Case: Used directly by the user Perform Sale User goals Sub-functionality Fill-in billing info Choose Products Alistair Cockburn “Writing Effective Use Cases” Introduction | Diagrams | Writing | Guidelines Inheritance Introduction | Diagrams | Writing | Guidelines.Breaking functionality into manageable chunks. ![]() Linking enables flexibility in requirements specification.Must be external to the system Humans Machines External systems Sensors Database Printer Organizational Units Introduction | Diagrams | Writing | GuidelinesĪctors can be generalized Example 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) Introduction | Diagrams | Writing | Guidelines.Must serve as sources and destinations for data.External objects that produce/consume data:.Customers Designers Users Introduction | Diagrams | Writing | GuidelinesĪ Simple Example Example Actors Association Use Case System boundary Introduction | Diagrams | Writing | Guidelines 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. (Why?) Introduction | Diagrams | Writing | Guidelines Requirements should raise a need, not answer it.If there are, tradeoffs must be detected and discussed. Requirements should not conflict with each other.They should cater for all current demands of the system.Each requirement must be interpreted in a single manner.Scenarios and reactions Introduction | Diagrams | Writing | Guidelines.Create a semi-formal model of the functional requirements.A document describing the use case in details admin Use Case in script Use case in diagram Introduction | Diagrams | Writing | Guidelines.A diagram, describing relations between use-cases and actors.A use case is a contract of an interaction between the system and an actor.“Database maintenance processes will occur every night” Introduction | Diagrams | Writing | Guidelines.“The user interface will be easy to use”.“The authorization process will take no more than 1 sec”.“Cash will be delivered after card was taken out”.“The system will deliver cash to the customer”.More detailed Introduction | Diagrams | Writing | Guidelinesįunctional Visible Requirements Hidden Functional Requirements Qualitative Requirements Types of Requirements.Introduction | Diagrams | Writing | Guidelines Final requirements are stabilized in an iterative process.Feasibility (technological, organizational etc).Advanced requirements come from the analysts, after studying:.Initial requirements come from the customer, by:.Where are we? Introduction | Diagrams | Writing | Guidelines Spring 2007 Session 3: Specifying Requirements with Use Case Diagrams Eran Toch
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