|By Dan Clark||
|April 28, 2003 12:00 AM EDT||
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.
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.
SYS-CON Events announced today that Isomorphic Software will exhibit at DevOps Summit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Isomorphic Software provides the SmartClient HTML5/AJAX platform, the most advanced technology for building rich, cutting-edge enterprise web applications for desktop and mobile. SmartClient combines the productivity and performance of traditional desktop software with the simp...
Aug. 28, 2016 03:30 AM EDT Reads: 2,337
With so much going on in this space you could be forgiven for thinking you were always working with yesterday’s technologies. So much change, so quickly. What do you do if you have to build a solution from the ground up that is expected to live in the field for at least 5-10 years? This is the challenge we faced when we looked to refresh our existing 10-year-old custom hardware stack to measure the fullness of trash cans and compactors.
Aug. 28, 2016 02:00 AM EDT Reads: 1,762
Extreme Computing is the ability to leverage highly performant infrastructure and software to accelerate Big Data, machine learning, HPC, and Enterprise applications. High IOPS Storage, low-latency networks, in-memory databases, GPUs and other parallel accelerators are being used to achieve faster results and help businesses make better decisions. In his session at 18th Cloud Expo, Michael O'Neill, Strategic Business Development at NVIDIA, focused on some of the unique ways extreme computing is...
Aug. 28, 2016 01:45 AM EDT Reads: 2,147
The emerging Internet of Everything creates tremendous new opportunities for customer engagement and business model innovation. However, enterprises must overcome a number of critical challenges to bring these new solutions to market. In his session at @ThingsExpo, Michael Martin, CTO/CIO at nfrastructure, outlined these key challenges and recommended approaches for overcoming them to achieve speed and agility in the design, development and implementation of Internet of Everything solutions wi...
Aug. 28, 2016 01:30 AM EDT Reads: 2,072
Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is expected in the amount of information being processed, managed, analyzed, and acted upon by enterprise IT. This amazing is not part of some distant future - it is happening today. One report shows a 650% increase in enterprise data by 2020. Other estimates are even higher....
Aug. 28, 2016 01:00 AM EDT Reads: 2,961
Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more business becomes digital the more stakeholders are interested in this data including how it relates to business. Some of these people have never used a monitoring tool before. They have a question on their mind like “How is my application doing” but no id...
Aug. 28, 2016 12:15 AM EDT Reads: 1,821
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportuni...
Aug. 27, 2016 11:00 PM EDT Reads: 3,994
Identity is in everything and customers are looking to their providers to ensure the security of their identities, transactions and data. With the increased reliance on cloud-based services, service providers must build security and trust into their offerings, adding value to customers and improving the user experience. Making identity, security and privacy easy for customers provides a unique advantage over the competition.
Aug. 27, 2016 08:45 PM EDT Reads: 2,345
Qosmos has announced new milestones in the detection of encrypted traffic and in protocol signature coverage. Qosmos latest software can accurately classify traffic encrypted with SSL/TLS (e.g., Google, Facebook, WhatsApp), P2P traffic (e.g., BitTorrent, MuTorrent, Vuze), and Skype, while preserving the privacy of communication content. These new classification techniques mean that traffic optimization, policy enforcement, and user experience are largely unaffected by encryption. In respect wit...
Aug. 27, 2016 08:45 PM EDT Reads: 1,775
Fact: storage performance problems have only gotten more complicated, as applications not only have become largely virtualized, but also have moved to cloud-based infrastructures. Storage performance in virtualized environments isn’t just about IOPS anymore. Instead, you need to guarantee performance for individual VMs, helping applications maintain performance as the number of VMs continues to go up in real time. In his session at Cloud Expo, Dhiraj Sehgal, Product and Marketing at Tintri, wil...
Aug. 27, 2016 06:15 PM EDT Reads: 739
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...
Aug. 27, 2016 06:00 PM EDT Reads: 3,095
Enterprises have forever faced challenges surrounding the sharing of their intellectual property. Emerging cloud adoption has made it more compelling for enterprises to digitize their content, making them available over a wide variety of devices across the Internet. In his session at 19th Cloud Expo, Santosh Ahuja, Director of Architecture at Impiger Technologies, will introduce various mechanisms provided by cloud service providers today to manage and share digital content in a secure manner....
Aug. 27, 2016 06:00 PM EDT Reads: 731
SYS-CON Events announced today that 910Telecom will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
Aug. 27, 2016 05:00 PM EDT Reads: 1,884
To leverage Continuous Delivery, enterprises must consider impacts that span functional silos, as well as applications that touch older, slower moving components. Managing the many dependencies can cause slowdowns. See how to achieve continuous delivery in the enterprise.
Aug. 27, 2016 04:45 PM EDT Reads: 1,636
There is growing need for data-driven applications and the need for digital platforms to build these apps. In his session at 19th Cloud Expo, Muddu Sudhakar, VP and GM of Security & IoT at Splunk, will cover different PaaS solutions and Big Data platforms that are available to build applications. In addition, AI and machine learning are creating new requirements that developers need in the building of next-gen apps. The next-generation digital platforms have some of the past platform needs a...
Aug. 27, 2016 04:00 PM EDT Reads: 588
Announcing @TelecomReseller Named “Media Sponsor” of @CloudExpo Silicon Valley | #IoT #Cloud #BigData
SYS-CON Events announced today Telecom Reseller has been named “Media Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
Aug. 27, 2016 03:15 PM EDT Reads: 775
DevOps at Cloud Expo – being held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real results. Am...
Aug. 27, 2016 02:45 PM EDT Reads: 3,452
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
Aug. 27, 2016 12:30 PM EDT Reads: 3,624
Traditional on-premises data centers have long been the domain of modern data platforms like Apache Hadoop, meaning companies who build their business on public cloud were challenged to run Big Data processing and analytics at scale. But recent advancements in Hadoop performance, security, and most importantly cloud-native integrations, are giving organizations the ability to truly gain value from all their data. In his session at 19th Cloud Expo, David Tishgart, Director of Product Marketing ...
Aug. 27, 2016 12:00 PM EDT Reads: 562
SYS-CON Events announced today that eCube Systems, a leading provider of middleware modernization, integration, and management solutions, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. eCube Systems offers a family of middleware evolution products and services that maximize return on technology investment by leveraging existing technical equity to meet evolving business needs. ...
Aug. 27, 2016 12:00 PM EDT Reads: 647