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An object-oriented application can easily become complex and difficult to understand. Programmers simplify this

complexity by using a leveling diagram, which depicts an application in layers, where the top level has the least amount of detail and is the easiest to understand. Subsequent levels have more detail and are usually the hardest to

understand.

Each level illustrates entities and processes. As the programmer drills down into the leveling diagram, they learn more details about each process. Figure 7-5 shows the first level of a leveling diagram that depicts how the bursar collects tuition from students.

Relationships Among Objects

Figure 7-5: The first level of the leveling diagram shows all the processes involved in how the bursar collects tuition from students.

Rectangles are used to represent entities, which are Student and Bursar in this example. Circles represent processes, such as registration, tuition, and payment of tuition. Also, two parallel lines are used to signify a data store, which is simply a place where data is stored. This example has two data stores: one that stores student information and another that stores tuition information. Arrows are used to show a movement of data among entities, processes, and data stores.

Notice that each process is assigned a unique number. This number is used to connect the first level with lower levels of the leveling diagram. Take a look at Figure 7-6 and you’ll see how this works.

Figure 7-6: Level 2 of the leveling diagram shows details of the Print Management Reports process from Level 1.

Relationships Among Objects

Figure 7-6 is the second level of the level diagram and describes the Print Management Reports process shown on Level 1. The Print Management Reports process actually has many subprocesses—one for each report. The second level shows these processes. Notice that each of the subprocesses is assigned a unique number. The number begins with corresponding number of the process shown on Level 1. Each of these subprocesses begins with 5, which is the number of the Print Management Reports process in Level 1.

The subprocess number contains a decimal followed by another number, which represents the subprocess in Level 2. For example, Print Student List By ID is the first subprocess on Level 2 and therefore is numbered 5.1. The number 5 links this subprocess to a process on Level 1, and the number 1 indicates this is the first subprocess on Level 2.

The same progression is used for subsequent levels. For example, you would look in Level 3 at process 5.1.1 to learn the details of the process used to print the student list by ID.

Quiz

Quiz

1. What is the difference between an attribute and data?

2. What is the purpose of using a leveling diagram?

3. What is an entity?

4. What is the purpose of using an entity relationship diagram?

5. What does 0:N mean?

6. What is the purpose of decomposing an attribute?

7. What is a processing model?

8. What is pseudo code?

9. What is a class diagram?

10. What is a many-to-one relationship?

Answers

1. An attribute is information used to describe an object, whereas data is the smallest amount of information used to describe an object. For example, a student name is an attribute, and a student’s first name and last name are data.

2. A leveling diagram is used to simplify the understanding of a complex application. The first level of the leveling diagram provides a simplified overview of the application, and subsequent levels provide a progressively more detailed view of the application.

3. Entity is another term used for “object.”

4. The purpose of using an entity relationship diagram is to illustrate the functional relationship between two or more entities that are not hierarchically related to each other.

5. 0:N is a ratio used in an entity relationship diagram to define a relationship. For example, 0:N in a student course relationship means that a student doesn’t have to register for any course and could register for many courses.

6. Decomposing an attribute is the process of reducing an attribute to data.

7. A processing model is a diagram that illustrates the steps in a behavior of an object.

8. Pseudo code is a textual description of a behavior that uses a combination of English words and programming language syntax.

9. A class diagram is an illustration that describes a class, its attributes, and its behaviors.

10. A many-to-one relationship defines the relationship between two entities where there are many instances of one entity to one instance of another. For example, many students are in one course.

Chapter 8: Real-World Modeling

Chapter 8: Real-World Modeling

Remember back during your grammar school days when you tried to shape a hunk of modeling clay into your favorite car? No matter how much you poked, pulled, and pounded, the clay never resembled an automobile. And yet

designers for auto manufacturers poke, pull, and pound the same clay as you, but are able to transform the hunk of clay into a work of art that eventually drives onto the showroom floor. Auto designers have the know-how to model a real-world automobile out of clay. The same can be said about professional object-oriented programmers. They have the skills to apply object-oriented programming theory to model real-world objects in a program. You’ll learn those skills in this chapter.