UML-CHP02_用例图 (2)

The user to use the system. The other software system that interact with the system. The other hardware system that interact with the system.
notice：sometimes timer may be regarded as an actor.
(2) A condition or capability that must be met or
possessed by a system or system component to satisfy a contract, standard, specification, or other formally imposed documents
name
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Use Cases and Actors
From the perspective of a given actor, a use case does something that is of value to the actor, such as calculate a result or change the state of an object. The Actors define the environments in which the system lives
User of mobile
Make a calling
Use cases is the objectives that the user want to achieve using the system.
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Need to notice observable result of value to an actor
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Actors
An actor represents a set of roles that users of use case play when interacting with these use cases. Actors can be human or automated systems. Actors are entities which require help from the system to perform their task or are needed to execute the system’s functions. Actors are not part of the system.
Object-Oriented Modeling
Chapter 2 Use case Modeling
高俊涛
东北石油大学
计算机与信息技术学院
计算机科学系
软件工程
Preface
From the first chapter, you already know that the first step in writing great software is making sure it does what the customer wants it to. But how do you figure out what a customer really wants? And how do you make sure that the customer even knows what they really want? In this chapter, you are going to learn how to satisfy you customer by making sure what you deliver is actually what they asked for.
name
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Specifying the Behavior of a Use Case
Describing the flow of events within the use case. Can be done in natural language, formal language or pseudo-code. Includes: how and when the use case starts and ends; when the use case interacts with actors and what objects are exchanged; the basic flow and alternative flows of the behavior.
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Contents 2.1 Software Requirements
The Concept The difficulty
2.2
Use Case Modeling
Building Blocks Relationships between use cases Guidelines for use case model
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How to identify an use case？
ＲＵＰ（Jacobson）：the instance of an use case is a set of actions of the system. These actions will bring obvious value to the user. An use case define a set of scenario (the instance of an use case)
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2.1 软件需求的概念
The complexity of requirements analysis
(2)Requirements keep changing Developers: The technology of communication is not enough Lack of knowledge of requirements engineering Don’t grasp the business processes of users Requirements are not clear and detailed The management of project is disorder
Use case is document, not the diagram ！
2.3
Conclusions软件工程2.1Fra bibliotek软件需求的概念
The Definition of Software Requirements
(1) A condition or capability needed by a user to solve
a problem or achieve an objective.
Actor
Use Case
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Use Case
Use cases specify desired behavior. A use case is a description of a set of sequences of actions that a system performs to yield an observable result of value to an actor. Describes a system from an external usage viewpoint.
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2.1 软件需求的概念
The complexity of requirements analysis
(2)Requirements keep changing Users： Knowledge about IT is not enough The description is not clear The importance of requirements is not understood Business scope keep changing Business process changing
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2.3 需求分析技术：功能分析
Example for Use Case
User of mobile Search for numbers
Sends Message
Make a phone call
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How to identify actors?
Actor is anyone or anything that interacts with the system causing it to respond to events． An actor may be：
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The process of use case modeling
Determine the scope of the system Determine the actors Determine the use cases Describe the use cases Define the relationships between use cases Review the use case model
通过输入电话号码拨打电话的场景 通过查打电话号码簿拨打电话的场景 通过查打电话号码簿拨打电话,电话打到一半电话欠费的场景
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The guideline to modeling use cases
Use cases are short texts Use cases may be an scenario Use cases may be a set of scenario Use cases don’t include design Use cases don’t include user interfaces Use cases don’t include testing the count of actions of a primary scenario is less than 9 The secondary scenario is more important that primary scenario