Welcome to this Video Learning Session. When you complete the session, you will be able to create object diagrams and models. Before you begin, you should review the previous session on object-oriented terms and concepts.
In this session, you’ll learn: What object modeling is, how to create object diagrams, and how to use a CASE tool for object modeling.
Object modeling sees an information system as a set of objects, such as people, places, events, and transactions. An object model uses various diagrams to show how objects behave, and how they perform real-world functions and tasks.
Suppose you want to model a Web-based order system that allows in-store pickup.
Each diagram type is like a camera that sees a different view. You start with an object relationship diagram.
Then you add: A use case diagram, a class diagram, a sequence diagram, a state-transition diagram, and an activity diagram.
Let’s review the diagrams one at a time.
An object-relationship diagram shows system objects and how they interact. This diagram shows an overview, so it’s a good way to start the object modeling process.
A use case diagram highlights events, transactions, and business processes, such as Add New Sales Rep, or Assign Accounts. The actors are shown as stick figures.
A use case diagram shows how each actor is involved with the use case, and with other actors.
A use case diagram must be documented carefully, with a description of the actors, successful completion, alternatives, pre-conditions, post-conditions, and any assumptions.
The next diagram is called a class diagram.
To create a class diagram, you use a concept called cardinality, which shows relationships between objects.
In this example, a sales manager can manage one sales office, a customer can place any number of orders, and an order can include any number of items.
Here are more examples:
An employee can have many payroll deductions, or none. This is called a zero or many relationship.
An employee can be single, or have one spouse. This is a zero or one relationship.
A manager is in charge of one and only one sales office, so it is a one and only one relationship.
An order can include one or many items, so it is a one or many relationship.
Let’s view the class diagram again. Now you can see how it uses cardinality notation to describe relationships among the objects.
A sequence diagram is like a flowchart that shows the actions and events. It uses a timeline to show the interaction among actors.
A state-transition diagram shows how an object changes from one state to another, based on specific events. It defines all possible states, or characteristics, of an object, and what causes the changes.
An activity diagram resembles a horizontal flowchart that shows actions and events. It shows the order in which actions occur, and identifies the outcomes.
In Part 2, you’ll get ready, grab your tools, and begin creating object diagrams.
You can’t create an accurate model without good documentation, so it’s important to prepare carefully. Here are some steps to follow.
First, you identify all the objects and describe them.
Then, list the actors who are using the system, describe all system events and transactions, and the states, or conditions that objects can have.
You’ll also need a timeline to keep things in order, and you’ll need to identify the outcomes, the actions that cause them, and the order in which they take place.
When it comes to tools, you have many choices. Applications like Visio, Word, and PowerPoint have built-in drawing tools that you can use.
Or, you can use special drawing and modeling tools. Some are expensive, some are shareware, and some offer free versions, like this one, which is quite powerful, and can create many types of object diagrams.
The most powerful modeling tools are CASE tools.
CASE stands for computer-aided software engineering. CASE tools can speed up development, improve quality, and reduce costs.
In Part 3 you’ll see how a CASE tool stores information in a central repository, like a library. This assures that the documentation is accurate, consistent, and easy to find.
Here’s an example of using a CASE tool to create a simple sequence diagram, like the one you saw earlier.
We’ll create a new diagram, and select a sequence diagram type from the list.
First, we’ll add an ACTIVE student who is a member of the STUDENT class.
Next, we’ll add a focus box for methods and messages into or out of this object.
Here are two more objects, an ADVISOR and a REGISTRAR, with their focus boxes.
We added an action called Update Information, which the REGISTRAR sends to the ADVISOR.
Next, the STUDENT meets with the ADVISOR, who Approves a schedule.
Here are the rest of the actions. Notice that a sequence diagram shows the order in which events occur.
And here’s the best part: All the objects and messages you created were automatically stored in the Repository. You can easily modify, update, or reuse them in other parts of the system. The result is consistency, better quality, and easier maintenance.
In this session you learned: What object modeling is, how to create object diagrams, and how to use a CASE tool for object modeling.
For more information, you can refer to the textbook or your Student Study Tool.
Now it’s Your Turn to apply your skills and check your work.
For background information, tasks to complete, and sample answers, go to the Management Information Systems CourseMate at www.cengagebrain.com. Select this text, and navigate to the Video Learning Sessions.
Thanks for attending this Video Learning Session.
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