Welcome!

Cloud Expo Authors: Yeshim Deniz, Pat Romanski, Esmeralda Swartz, Carmen Gonzalez, Roger Strukhoff

Related Topics: .NET

.NET: Article

The UML Class Diagram

The UML Class Diagram

The class diagram is an excellent aid to model the attributes, operations, and associations of the classes in your applications. This article, the second in a series of articles that introduce the reader to the concepts of object-oriented design and the Unified Modeling Language, focuses on UML class diagrams. It reviews UML class diagramming notation and the use of Visio to construct a class diagram.

The Need for Modeling Classes
Class structures are fundamental to any object-oriented programming language. The class structure is a template for the objects that will implement the functionality of your applications. As a .NET developer, you need to become increasingly familiar with the classes available in the .NET Framework. As you gain experience developing .NET applications you will discover the need to develop your own class libraries. Good design of object-oriented applications dictates a clear separation of functionality between the user interface, business logic, and data access logic. Well-designed applications achieve this separation of functionality through the development of class libraries that encapsulate internal processing. By developing class libraries, your applications become more manageable, scalable, and extendable.

An all-too-common problem in many object-oriented applications is a lack of preplanning. Class libraries evolve haphazardly. As a result, the distinction of roles and responsibilities among the various classes in the library becomes muddled and convoluted. These class libraries are difficult to manage, revise, and employ. This is especially problematic when large teams of developers build an application. Employing a tool to model your class libraries is imperative to ensure that the application remains consistent, manageable, and clearly defined. A UML class diagram is an excellent tool for modeling the structure of your class libraries.

Modeling Class Structure Using UML
In a UML class diagram, a rectangle divided into three parts represents the class. The top section contains the name of the class, the middle section contains the attributes of the class, and the lower section contains the operations performed by the class. Operations may take the form of methods, constructors, destructors, properties, or events. Figure 1 illustrates a UML class diagram representing a loan class. This class is part of a library loan application that tracks loan, member, and inventory information for a small library.

Examining the class diagram reveals that along with the name of the attribute, it defines the attribute's accessibility. A minus sign (-) in front of the attribute name indicates it is private. A plus sign (+) indicates it is public, and a pound sign (#) indicates it is protected. A private element is only accessible from within the class. A public element is accessible from any code in the same project or any project with a reference to the project containing the class. A protected element is accessible from within the class and any class derived from the class.

Although the UML specifications do not define specific data types, when developing classes for use in .NET assemblies you can strongly type the attributes using the supported types of your implementation language. Visio allows the choice of either VB, C#, C++, or IDL supported data types. Data types can also be complex data types defined by your class library or the .NET class library. For example, a catalog class may have an item attribute that is of type System.Data.DataRow. Another possible scenario would be to create a catalog class as a collection class whose item attribute is an Item class type.

The lower section of the UML class shape defines the operations of the class. Typically, the class diagram will define the name of the operation, its accessibility, any parameters passed in to the operation, and any return value passed back when the operation executes. The loan class represented in Figure 1 contains two constructors (Sub New), a function (CalculateDueDate), an event procedure (OverDueNotice), and a property (LoanID). Unfortunately, the UML specifications do not define a way to identify the various operation types in the diagram. You can, however, add your own notation to indicate the various types depending on the modeling tool you use. Figure 2 shows the loan class shape with custom stereotypes added to identify the various operations defined in the diagram.

Modeling Class Associations
When a class refers to or uses another class, the classes form an association. For example, in the library loan application we have identified the need to construct a Loan class and a Book class. The responsibility of the Loan class is to maintain information about a book out on loan. This includes the member who has the book, the book, and the due date. The responsibility of the Book class is to maintain relevant information about the book. This includes ISBN, title, author, and publisher. Since the Loan class maintains a reference to the Book class, the book class is a collaborator of the Loan class. A line connecting the two classes represents this association in the class diagram. The association line often includes a label to describe the association.

Association lines can also indicate the direction of the association. In the previous case, the Loan class maintains a reference to the Book class, but the book class does not maintain a reference to the Loan class. To depict a one-way association, you add an arrow to the association line. The class diagram shown in Figure 3 documents the association between the loan class and the book class.

Sometimes a single instance of one class associates with multiple instances of another class. For example, a member may have multiple books out on loan. In this case, a single instance of a member class is associated with multiple instances of the Loan class. Multiplicity is included in the class diagram by placing the appropriate symbol on the association line. The class diagram in Figure 4 indicates that an instance of the Member class may be associated with multiple instances of the Loan class.

Using Visio to Construct a Class Diagram
Now that you're familiar with some of the notations used to construct a class diagram, you are ready to investigate the use of Visio to create class diagrams. If you do not have Visio installed, you can still benefit from following along and completing the diagram with paper and pencil.
1.   Start up Visio. From the File menu choose New -> Software -> UML Model Diagram.
2.   Locate the Shapes window along the left side of the screen. This window includes a tab for the common UML diagrams. Select the UML Static Structure tab (see Figure 5).
3.   From the Shapes window click and drag the Class shape onto the design surface. Right-click the Class shape on the design surface and choose Properties. A UML Class Properties window becomes visible (see Figure 6). Change the name to "Book" and add the description "Responsible for maintaining book information" in the Documentation text box.
4.   Select Attributes on the Categories list box in the left side of the window. Click on the New button on the right side of the window to add a new attribute to the class. Click on the Properties button to display the UML Attribute Properties window. Change the name of the attribute to "mISBN". Change the type to "VB::Char" and verify that the visibility is "private". Click the OK button to return to the UML Class Properties window.
5.   Select Operations in the Categories list box on the left side of the window. Click on the New button on the right side of the window to add a new operation to the class. Click on the Properties button to display the UML Operation Properties window. Change the name of the operation to "ISBN". Change the return type to "VB::Char" and verify that the visibility is "public". Select "Code Generation Options" in the Categories list box on the left side of the window. Change the operation kind to "Property" and check the "Create Get Method" and "Create Set Method" check boxes to indicate it is a readable/writable property. Click the OK button to return to the UML Class Properties window.
6.   Select Operations in the Categories list box on the left side of the window. Click on the New button on the left side of the window to add a new operation to the class. Click on the Properties button to display the UML Operation Properties window. Change the name of the operation to "CheckAvailability". Change the return type to "VB::Boolean" and verify that the visibility is "public". Select "Parameters" in the Categories list box on the left side of the window. Click on the New button on the right side of the window to add a new parameter to the operation. Click on the Properties button to display the UML Parameter Properties window. Change the name of the parameter to "ReservationDate" and the type to "VB::Date". Click the OK button to return to the UML Operation Properties window. Click the OK button to return to the UML Class Properties window. Click OK to close the UML Class Properties window. The Book class diagram should look similar to the one shown in Figure 7.
7.   In order to demonstrate the creation of class associations, add a Member class and a Loan class to the class diagram. If you want some practice, add some attributes and operations to these classes.
8.   From the Shapes window, click and drag the Binary Association shape onto the design surface. Attach end 1 of the Binary Association to the Member class and end 2 to the Loan class. The Binary Association line will turn red if it is not attached properly. Right-click the Binary Association shape on the design surface and choose Properties. The UML Association Properties window will display. Change the name of the association to "Takes Out". Change the Name Reading Direction to "forward". Change End 1's multiplicity to 1 and check the IsNavigable check box. When you are finished, click OK to close the window.
9.   Right-click the "Takes Out" Binary Association shape on the design surface and choose Shape Display Options. The UML Shape Display Options window displays. Under the General section, click the Name check box. Under the Suppress section, click on the First end and Second end check boxes. When finished, click OK.
10.   Figure 8 shows the completed diagram, including an association between the Loan class and the Book class. For additional practice, add this association to your diagram.

Conclusion
This article has introduced you to using the Unified Modeling Language to model the class structure of your application. The class diagram is a great aid for modeling the attributes and operations of the classes that make up your application. The class diagram also shows how the various classes in your application associate with each other. A CASE tool such as Visio, although not necessary, is beneficial in the creation of the class diagram.

A future article will continue the study of UML and class associations, focusing on modeling class inheritance hierarchies. In addition, you will be introduced to modeling interfaces, meta classes, and utility classes, which are all commonly used in class library applications. Finally, you will experience using Visio to generate a Visual Studio .NET class library from the UML model.

More Stories By Dan Clark

Dan is a Microsoft Certified Trainer, Microsoft Certified Solution Developer, and a Microsoft Certified Database Administrator. For the past seven years he has been developing applications and training others how to develop applications using Microsoft technologies. Dan has been developing and training Microsoft's .NET technologies since the early betas. He has recently authored the book "An Introduction to Object-Oriented Programming with Visual Basic .NET," published by Apress.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@CloudExpo Stories
SYS-CON Events announced today that Verizon has been named "Gold Sponsor" of SYS-CON's 15th International Cloud Expo®, which will take place on November 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Verizon Enterprise Solutions creates global connections that generate growth, drive business innovation and move society forward. With industry-specific solutions and a full range of global wholesale offerings provided over the company's secure mobility, cloud, strategic network...
Blue Box has closed a $10 million Series B financing. The round was led by a strategic investor and included participation from prior investors including Voyager Capital and Founders Collective, as well as the Blue Box executive team. This round follows a $4.3 million Series A closed in December of 2012 and led by Voyager Capital. In May of this year, the company announced general availability of its private cloud as a service offering, Blue Box Cloud. Since that release, the company has dem...
Ixia develops amazing products so its customers can connect the world. Ixia helps its customers provide an always-on user experience through fast, secure delivery of dynamic connected technologies and services. Through actionable insights that accelerate and secure application and service delivery, Ixia's customers benefit from faster time to market, optimized application performance and higher-quality deployments.
SimpleECM is the only platform to offer a powerful combination of enterprise content management (ECM) services, capture solutions, and third-party business services providing simplified integrations and workflow development for solution providers. SimpleECM is opening the market to businesses of all sizes by reinventing the delivery of ECM services. Our APIs make the development of ECM services simple with the use of familiar technologies for a frictionless integration directly into web applicat...
The only place to be June 9-11 is Cloud Expo & @ThingsExpo 2015 East at the Javits Center in New York City. Join us there as delegates from all over the world come to listen to and engage with speakers & sponsors from the leading Cloud Computing, IoT & Big Data companies. Cloud Expo & @ThingsExpo are the leading events covering the booming market of Cloud Computing, IoT & Big Data for the enterprise. Speakers from all over the world will be hand-picked for their ability to explore the economic...
Cloudwick, the leading big data DevOps service and solution provider to the Fortune 1000, announced Big Loop, its multi-vendor operations platform. Cloudwick Big Loop creates greater collaboration between Fortune 1000 IT staff, developers and their database management systems as well as big data vendors. This allows customers to comprehensively manage and oversee their entire infrastructure, which leads to more successful production cluster operations, and scale-out. Cloudwick Big Loop supports ...
To manage complex web services with lots of calls to the cloud, many businesses have invested in Application Performance Management (APM) and Network Performance Management (NPM) tools. Together APM and NPM tools are essential aids in improving a business’s infrastructure required to support an effective web experience… but they are missing a critical component – Internet visibility. Internet connectivity has always played a role in customer access to web presence, but in the past few years use...
SAP is delivering break-through innovation combined with fantastic user experience powered by the market-leading in-memory technology, SAP HANA. In his General Session at 15th Cloud Expo, Thorsten Leiduck, VP ISVs & Digital Commerce, SAP, will discuss how SAP and partners provide cloud and hybrid cloud solutions as well as real-time Big Data offerings that help companies of all sizes and industries run better. SAP launched an application challenge to award the most innovative SAP HANA and SAP ...
Software AG helps organizations transform into Digital Enterprises, so they can differentiate from competitors and better engage customers, partners and employees. Using the Software AG Suite, companies can close the gap between business and IT to create digital systems of differentiation that drive front-line agility. We offer four on-ramps to the Digital Enterprise: alignment through collaborative process analysis; transformation through portfolio management; agility through process automation...
What are the benefits of using an enterprise-grade orchestration platform? In their session at 15th Cloud Expo, Jeff Tegethoff, CEO of Appcore, and Kedar Poduri, Senior Director of Product Management at Citrix Systems, will take a closer look at the architectural design factors needed to support diverse workloads and how to run these workloads efficiently as a service provider. They will also discuss how to deploy private cloud environments in 15 minutes or less.
Headquartered in Santa Monica, California, Bitium was founded by Kriz and Erik Gustavson. The 1,500 cloud-based application using Bitium’s analytics, app management, and single sign-on services include bug trackers, customer service dashboards, Google Apps, and social networks. The firm states website administrators can do multiple tasks online without revealing passwords. Bitium’s advisors include Microsoft’s former CMO and the former senior vice president of strategy, the founder and CEO of Li...
The Transparent Cloud-computing Consortium (abbreviation: T-Cloud Consortium) will conduct research activities into changes in the computing model as a result of collaboration between "device" and "cloud" and the creation of new value and markets through organic data processing High speed and high quality networks, and dramatic improvements in computer processing capabilities, have greatly changed the nature of applications and made the storing and processing of data on the network commonplace. ...
StackIQ offers a comprehensive software suite that automates the deployment, provisioning, and management of Big Infrastructure. With StackIQ’s software, you can spin up fully configured big data clusters, quickly and consistently — from bare-metal up to the applications layer — and manage them efficiently. Our software’s modular architecture allows customers to integrate nearly any application with the StackIQ software stack.
Things are being built upon cloud foundations to transform organizations. This CEO Power Panel at 15th Cloud Expo, moderated by Roger Strukhoff, Cloud Expo and @ThingsExpo conference chair, will address the big issues involving these technologies and, more important, the results they will achieve. How important are public, private, and hybrid cloud to the enterprise? How does one define Big Data? And how is the IoT tying all this together?
The Internet of Things (IoT) is going to require a new way of thinking and of developing software for speed, security and innovation. This requires IT leaders to balance business as usual while anticipating for the next market and technology trends. Cloud provides the right IT asset portfolio to help today’s IT leaders manage the old and prepare for the new. Today the cloud conversation is evolving from private and public to hybrid. This session will provide use cases and insights to reinforce t...
TechCrunch reported that "Berlin-based relayr, maker of the WunderBar, an Internet of Things (IoT) hardware dev kit which resembles a chunky chocolate bar, has closed a $2.3 million seed round, from unnamed U.S. and Switzerland-based investors. The startup had previously raised a €250,000 friend and family round, and had been on track to close a €500,000 seed earlier this year — but received a higher funding offer from a different set of investors, which is the $2.3M round it’s reporting."...
The 3rd International Internet of @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
The Industrial Internet revolution is now underway, enabled by connected machines and billions of devices that communicate and collaborate. The massive amounts of Big Data requiring real-time analysis is flooding legacy IT systems and giving way to cloud environments that can handle the unpredictable workloads. Yet many barriers remain until we can fully realize the opportunities and benefits from the convergence of machines and devices with Big Data and the cloud, including interoperability, da...
All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades. Over the summer Gartner released its much anticipated annual Hype Cycle report and the big news is that Internet of Things has now replaced Big Data as the most hyped technology. Indeed, we're hearing more and more about this fascinating new technological paradigm. ...
In his session at 15th Cloud Expo, Mark Hinkle, Senior Director, Open Source Solutions at Citrix Systems Inc., will provide overview of the open source software that can be used to deploy and manage a cloud computing environment. He will include information on storage, networking(e.g., OpenDaylight) and compute virtualization (Xen, KVM, LXC) and the orchestration(Apache CloudStack, OpenStack) of the three to build their own cloud services.