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In software and systems engineering , a use case is a list of actions or event steps typically defining the interactions between a role known in the Unified Modeling Language UML as an actor and a system to achieve a goal. The actor can be a human or other external system. In systems engineering, use cases are used at a higher level than within software engineering , often representing missions or stakeholder goals. In he co-authors the book Object-Oriented Software Engineering - A Use Case Driven Approach ,  which laid the foundation of the OOSE system engineering method and helped to popularize use cases for capturing functional requirements , especially in software development. In he publishes a book about use cases and object-oriented techniques applied to business models and business process reengineering.
In software and systems engineering , a use case is a list of actions or event steps typically defining the interactions between a role known in the Unified Modeling Language UML as an actor and a system to achieve a goal.
The actor can be a human or other external system. In systems engineering, use cases are used at a higher level than within software engineering , often representing missions or stakeholder goals. In he co-authors the book Object-Oriented Software Engineering - A Use Case Driven Approach ,  which laid the foundation of the OOSE system engineering method and helped to popularize use cases for capturing functional requirements , especially in software development. In he publishes a book about use cases and object-oriented techniques applied to business models and business process reengineering.
The resulting Unified Process is published in and promotes a use case driven approach. Since then, many authors have contributed to the development of the technique, notably: Larry Constantine develops in , in the context of usage-centered design , so called "essential use-cases" that aim to describe user intents rather than sequences of actions or scenarios which might constraint or bias the design of user interface;  Alistair Cockburn publishes in a goal-oriented use case practice based on text narratives and tabular specifications;  Kurt Bittner and Ian Spence develop in advanced practices for analyzing functional requirements with use cases;  Dean Leffingwell and Don Widrig propose to apply use cases to change management and stakeholder communication activities;  Gunnar Overgaard proposed in to extend the principles of design patterns to use cases.
Use cases are a technique for capturing, modelling and specifying the requirements of a system. Actors represent the role that human users or other systems have in the interaction. In the requirement analysis , at their identification, a use case is named according to the specific user-goal that it represents for its primary actor.
The case is further detailed with a textual description or with additional graphical models that explains the general sequence of activities and events, as well as variants such as special conditions, exceptions or error situations. According to the Software Engineering Body of Knowledge SWEBOK ,  use cases belong to the scenario-based requirement elicitation techniques, as well as the model-based analysis techniques.
But the use cases also supports narrative-based requirement gathering, incremental requirement acquisition, system documentation, and acceptance testing. There are many ways to write a use case in text, from use case brief , casual , outline , to fully dressed etc. Writing use cases in templates devised by various vendors or experts is a common industry practice to get high-quality functional system requirements. The template defined by Alistair Cockburn in his book Writing Effective Use Cases has been one of the most widely used writing styles of use cases.
Cockburn suggests annotating each use case with a symbol to show the "Design Scope", which may be black-box internal detail is hidden or white-box internal detail is shown.
Five symbols are available: . Other authors sometimes call use cases at Organization level "Business use cases". Cockburn suggests annotating each use case with a symbol to show the "Goal Level";  the preferred level is "User-goal" or colloquially "sea level"  : Sometimes in text writing, a use case name followed by an alternative text symbol!
Cockburn describes a more detailed structure for a use case, but permits it to be simplified when less detail is needed. His fully dressed use case template lists the following fields: .
In addition, Cockburn suggests using two devices to indicate the nature of each use case: icons for design scope and goal level. Cockburn's approach has influenced other authors; for example, Alexander and Beus-Dukic generalize Cockburn's "Fully dressed use case" template from software to systems of all kinds, with the following fields differing from Cockburn: . Cockburn recognizes that projects may not always need detailed "fully dressed" use cases.
He describes a Casual use case with the fields: . Martin Fowler states "There is no standard way to write the content of a use case, and different formats work well in different cases. A use case defines the interactions between external actors and the system under consideration to accomplish a goal. Actors must be able to make decisions, but need not be human: "An actor might be a person, a company or organization, a computer program, or a computer system—hardware, software, or both.
Similarly, a person using a system may be represented as different actors because of playing different roles. For example, user "Joe" could be playing the role of a Customer when using an Automated Teller Machine to withdraw cash from his own account, or playing the role of a Bank Teller when using the system to restock the cash drawer on behalf of the bank.
Actors are often working on behalf of someone else. Cockburn writes that "These days I write 'sales rep for the customer' or 'clerk for the marketing department' to capture that the user of the system is acting for someone else. A stakeholder may play both an active and an inactive role: for example, a Consumer is both a "mass-market purchaser" not interacting with the system and a User an actor, actively interacting with the purchased product.
Cockburn advises to look for actors among the stakeholders of a system, the primary and supporting secondary actors of a use case, the system under design SuD itself, and finally among the "internal actors", namely the components of the system under design. The primary difference is that the system considered in a business use case model may contain people in addition to technological systems. These "people in the system" are called business workers. In the example of a restaurant, a decision must be made whether to treat each person as an actor thus outside the system or a business worker inside the system.
If a waiter is considered an actor, as shown in the example below, then the restaurant system does not include the waiter, and the model exposes the interaction between the waiter and the restaurant. An alternative would be to consider the waiter as a part of the restaurant system a business worker , while considering the client to be outside the system an actor.
Use cases are not only texts, but also diagrams, if needed. In the Unified Modeling Language , the relationships between use cases and actors are represented in use case diagrams originally based upon Ivar Jacobson 's Objectory notation.
SysML uses the same notation at a system block level. In addition, other behavioral UML diagrams such as activity diagrams , sequence diagrams , communication diagrams and state machine diagrams can also be used to visualize use cases accordingly. Specifically, a System Sequence Diagram SSD is a sequence diagram often used to show the interactions between the external actors and the system under design SuD , usually for visualizing a particular scenario of a use case.
Use case analysis usually starts by drawing use case diagrams. For agile development, a requirement model of many UML diagrams depicting use cases plus some textual descriptions, notes or use case briefs would be very lightweight and just enough for small or easy project use.
As good complements to use case texts, the visual diagram representations of use cases are also effective facilitating tools for the better understanding, communication and design of complex system behavioral requirements. Below is a sample use case written with a slightly-modified version of the Cockburn-style template.
Note that there are no buttons, controls, forms, or any other UI elements and operations in the basic use case description, where only user goals, subgoals or intentions are expressed in every step of the basic flow or extensions.
This practice makes the requirement specification clearer, and maximizes the flexibility of the design and implementations. Brief : equivalent to a user story or an epic. Since the inception of the agile movement, the user story technique from Extreme Programming has been so popular that many think it is the only and best solution for agile requirements of all projects.
Alistair Cockburn lists five reasons why he still writes use cases in agile development. In summary, specifying system requirements in use cases has these apparent benefits comparing with traditional or other approaches:. Use cases constitute a powerful, user-centric tool for the software requirements specification process. These user goals then become the ideal candidates for the names or titles of the use cases which represent the desired functional features or services provided by the system.
This user-centered approach ensure that what has the real business value and the user really want is developed, not those trivial functions speculated from a developer or system inside perspective.
Use case authoring has been an important and valuable analysis tool in the domain of User-Centered Design UCD for years. Use cases are often written in natural languages with structured templates. This narrative textual form legible requirement stories , understandable by almost everyone, complemented by visual UML diagrams foster better and deeper communications among all stakeholders, including customers, end-users, developers, testers and managers.
Better communications result in quality requirements and thus quality systems delivered. Analyzing a use case step by step from preconditions to postconditions, exploring and investigating every action step of the use case flows, from basic to extensions, to identify those tricky, normally hidden and ignored, seemingly trivial but realistically often costly requirements as Cockburn mentioned above , is a structured and beneficial way to get clear, stable and quality requirements systematically.
Minimizing and optimizing the action steps of a use case to achieve the user goal also contribute to a better interaction design and user experience of the system. With content based upon an action or event flow structure, a model of well-written use cases also serves as an excellent groundwork and valuable guidelines for the design of test cases and user manuals of the system or product, which is an effort-worthy investment up-front.
There is obvious connections between the flow paths of a use case and its test cases. Deriving functional test cases from a use case through its scenarios running instances of a use case is straightforward. User stories are agile; use cases are not. Agile and Scrum are neutral on requirement techniques. As the Scrum Primer  states,. Product Backlog items are articulated in any way that is clear and sustainable. Contrary to popular misunderstanding, the Product Backlog does not contain "user stories"; it simply contains items.
Those items can be expressed as user stories, use cases, or any other requirements approach that the group finds useful. But whatever the approach, most items should focus on delivering value to customers.
Use case techniques have evolved to take Agile approaches into account by using use case slices to incrementally enrich a use case. Craig Larman stresses that "use cases are not diagrams, they are text". Use cases will often contain a level of detail i. Novice misunderstandings. Each step of a well-written use case should present actor goals or intentions the essence of functional requirements , and normally it should not contain any user interface details, e.
As for capturing requirements for a new system from scratch, use case diagrams plus use case briefs are often used as handy and valuable tools, at least as lightweight as user stories. The format of the use case makes it difficult to describe a large system e.
CRM system in less than several hundred pages. It is time consuming and you will find yourself spending time doing an unnecessary amount of rework.
Spending much time in writing tedious use cases which add no or little value and result in a lot of rework is a bad smell indicating that the writers are not well skilled and have little knowledge of how to write quality use cases both efficiently and effectively.
Use cases should be authored in an iterative, incremental and evolutionary agile way. Applying use case templates does not mean that all the fields of a use case template should be used and filled out comprehensively from up-front or during a special dedicated stage, i.
In fact, the use case formats formulated by those popular template styles , e. The quality of a good use case documentation model should not be judged largely or only by its size.
It is possible as well that a quality and comprehensive use case model of a large system may finally evolve into hundreds of pages mainly because of the inherent complexity of the problem in hand, not because of the poor writing skills of its authors.
For large and complex system requirements, dedicated use case tools are helpful. Most UML tools support both the text writing and visual modeling of use cases. From Wikipedia, the free encyclopedia. Main article: Actor UML. This section needs expansion. You can help by adding to it. July This section does not cite any sources. Please help improve this section by adding citations to reliable sources.
Use Cases in Practice:: A Study in the Norwegian Software Industry
Here we provide some examples of UML use case diagrams. Purpose : An example of a business use case diagram for airport check-in and security screening. Purpose : Two alternative examples of business use case diagram for a Restaurant - external and internal business views of a restaurant. Summary : Several business actors having some needs and goals as related to the restaurant and business use cases expressing expectations of the actors from the business. Purpose : Show that ticket vending machine allows commuters to buy tickets.
viewed from the outside, e.g., by a user, using specific examples. Note on For the second question, the student chooses to edit a previous answer. Student A.
use case diagram exam questions and answers
Use Case Diagram captures the system's functionality and requirements by using actors and use cases. Use Cases model the services, tasks, function that a system needs to perform. Use cases represent high-level functionalities and how a user will handle the system.
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