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Foundations of Programming: Object-Oriented Design
Illustration by Mark Todd

Identifying the actors


From:

Foundations of Programming: Object-Oriented Design

with Simon Allardice

Video: Identifying the actors

An Actor in a use case is anything with behavior who lives outside of your system, outside of your application, but has a goal they want to accomplish within. And these are usually human beings, but not always. Now sometimes coming up with the actor is very straightforward. If you're building a Calculator App for a mobile device or a simple one person game, you may just have one actor, someone who uses the application, the user. However, if you were building, say, a backend internal Payroll Application, you might have multiple people that do very different goals within such as the payroll administrator, or a manager, or an employee, and you also need to interact with other computer systems.
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  1. 11m 35s
    1. Welcome
      1m 25s
    2. Who this course is for
      1m 15s
    3. What to expect from this course
      3m 6s
    4. Exploring object-oriented analysis, design, and development
      1m 41s
    5. Reviewing software development methodologies
      4m 8s
  2. 26m 14s
    1. Why we use object-orientation
      2m 42s
    2. What is an object?
      5m 22s
    3. What is a class?
      4m 43s
    4. What is abstraction?
      2m 45s
    5. What is encapsulation?
      3m 45s
    6. What is inheritance?
      3m 35s
    7. What is polymorphism?
      3m 22s
  3. 12m 16s
    1. Understanding the object-oriented analysis and design processes
      4m 13s
    2. Defining requirements
      6m 9s
    3. Introduction to the Unified Modeling Language (UML)
      1m 54s
  4. 23m 35s
    1. Understanding use cases
      6m 11s
    2. Identifying the actors
      4m 16s
    3. Identifying the scenarios
      5m 7s
    4. Diagramming use cases
      4m 18s
    5. Employing user stories
      3m 43s
  5. 16m 36s
    1. Creating a conceptual model
      1m 59s
    2. Identifying the classes
      2m 27s
    3. Identifying class relationships
      2m 38s
    4. Identifying class responsibilities
      6m 43s
    5. Using CRC cards
      2m 49s
  6. 22m 25s
    1. Creating class diagrams
      6m 11s
    2. Converting class diagrams to code
      4m 57s
    3. Exploring object lifetime
      5m 55s
    4. Using static or shared members
      5m 22s
  7. 19m 49s
    1. Identifying inheritance situations
      6m 49s
    2. Using inheritance
      2m 43s
    3. Using abstract classes
      2m 2s
    4. Using interfaces
      4m 20s
    5. Using aggregation and composition
      3m 55s
  8. 9m 23s
    1. Creating sequence diagrams
      5m 18s
    2. Working with advanced UML diagrams
      2m 3s
    3. Using UML tools
      2m 2s
  9. 10m 39s
    1. Introduction to design patterns
      2m 40s
    2. Example: the singleton pattern
      4m 53s
    3. Example: the memento pattern
      3m 6s
  10. 21m 47s
    1. Introduction to object-oriented design principles
      2m 50s
    2. Exploring general development principles
      3m 55s
    3. Introduction to SOLID principles
      6m 43s
    4. Introduction to GRASP principles
      8m 19s
  11. 7m 1s
    1. Reviewing feature support across different object-oriented languages
      3m 50s
    2. Additional resources
      2m 27s
    3. Goodbye
      44s

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Foundations of Programming: Object-Oriented Design
3h 1m Intermediate May 22, 2012

Viewers: in countries Watching now:

Most modern programming languages, such as Java, C#, Ruby, and Python, are object-oriented languages, which help group individual bits of code into a complex and coherent application. However, object-orientation itself is not a language; it's simply a set of ideas and concepts.

Let Simon Allardice introduce you to the terms—words like abstraction, inheritance, polymorphism, subclass—and guide you through defining your requirements and identifying use cases for your program. The course also covers creating conceptual models of your program with design patterns, class and sequence diagrams, and unified modeling language (UML) tools, and then shows how to convert the diagrams into code.

Topics include:
  • Why use object-oriented design (OOD)?
  • Pinpointing use cases, actors, and scenarios
  • Identifying class responsibilities and relationships
  • Creating class diagrams
  • Using abstract classes
  • Working with inheritance
  • Creating advanced UML diagrams
  • Understanding object-oriented design principles
Subjects:
Developer Design Patterns Programming Foundations
Software:
Java
Author:
Simon Allardice

Identifying the actors

An Actor in a use case is anything with behavior who lives outside of your system, outside of your application, but has a goal they want to accomplish within. And these are usually human beings, but not always. Now sometimes coming up with the actor is very straightforward. If you're building a Calculator App for a mobile device or a simple one person game, you may just have one actor, someone who uses the application, the user. However, if you were building, say, a backend internal Payroll Application, you might have multiple people that do very different goals within such as the payroll administrator, or a manager, or an employee, and you also need to interact with other computer systems.

Perhaps this application will send data to an external system or it needs to interact with another corporate system. Well, these would be considered actors too. They're external to your application, but they need to interact with it. So it's usual to spend a few minutes brainstorming the main actors, and we can actually start with one easy question. Does your App need to interact with other computer systems, other organization? Because even if the Use Case Scenario is complex with these external systems just identifying them as an Actor should be fairly straightforward, and that's all we're doing here.

Now switching to human actors, here's a couple of questions. Do you need to distinguish between Roles or Security Groups? Say if you're building a web application, you might have very different use cases for visitors and for members and for administrators. If you're working on an internal corporate application, thinking about different job titles or departments can also prompt these scenarios. How does the data entry staff interact with the application as opposed to the executive team? Although the idea of the security level or a roll or even a job title might prompt a particular scenario, a particular use case, or make you think of something that you need to write, always do remember that the focus is on the goal that the actor wants to accomplish, and that the same person in the same job title in the same role could actually be different actors on different days.

Now what I mean by that is if you're defining, say, a use case for a new internal Expense Approval System, that might be true that your organization has employees and contractors, full-time and part-time, administrators, managers, executives, all who expect to interact with this application. But the difference between them might not matter at all. If this particular situation comes down to somebody requests and somebody approves, all that might be needed to describe this completely successfully is that you phrase the actor Requester and Approver.

Not a job title, not a specific role, but a perfectly acceptable name for the actors who take part in this particular use case. And it's quite common as in this situation that use cases will involve multiple actors, and we'll typically refer to them as the primary actors and the supporting actors. Now the primary actors aren't necessarily the most important actor in the scenario. They're just the one who initiated this particular use case. So with this situation the primary actor is the Requester.

Anyone else is a secondary actor. So these are just a few of the ways you could brainstorm a quick list of primary actors of your system. Now because sometimes the actors will suggest the goals and sometimes the goals will suggest the actors, both of these are okay, whatever feels most natural. But one thing to bear in mind, the goals of an actor don't always succeed. A use case scenario for a bank might have the account holder actor who has the goal to transfer funds between accounts, and you should start up by describing the successful steps for that.

But you may well need to describe the alternative flow of not enough funds. Goals sometimes fail, and that leads us into talking more about sketching out those Scenarios and goals that the actors want to accomplish.

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