CSC/ECE 517 Fall 2009/wiki1b 13 a1

History and Applications of the MVC Pattern

Introduction

The Model View Controller (MVC) is an architectural design pattern for object-oriented software applications. MVC proposes the use of three different types of components to handle core application functionality. Each component has a distinct and specialized responsibility. The components of an MVC application are: a model, a view, and a controller.

• The model handles the data which is used by the application. The functionality provided by the model includes retrieving data from its source, usually a relational database, and saving such data once it has changed. The model also enforces the business logic needed to preserve the validity of the data.

• The view handles the presentation of the data or portions of it in a way that is accessible to the user, usually a Graphical User Interface (GUI). The view is solely concerned with the display of the data and does not perform any validation or business logic.

• The controller is in charge of processing the interaction between the user and the application. The controller determines which model methods should be invoked in response to user actions. Once data is delivered by the model, the controller also determines which view should display it. In the case of web applications, the controller is where navigation logic is processed [10, 15].

The following diagram illustrates a typical scenario for a web application implemented using the MVC pattern.

History

The MVC pattern was first proposed by "Trygve Reenskaugh in 1979 and implemented by Jim Althoff for Smalltalk-80 [8]." The first implementation of MVC took place at the Xerox PARC research lab as part of the Smalltalk-80 user interface [7]. Smalltalk-80 was a highly interactive graphical user interface which became the precursor of the Apple Lisa and later the Macintosh. The principles of MVC have largely influenced the software developed for the Mac.

The MVC was originally conceived for the implementation of interactive desktop applications with a graphical user interface. Other than the work on Smalltalk and Apple, MVC did not enjoy much popularity in subsequent years. The advent of the web changed things. Initial web applications were written with little or no separation of concerns. A typical web application would combine presentation, business, and data retrieval logic on a single file of code. As applications became more complex, maintenance issues became apparent. Developers started looking for ways to better structure web applications, which resulted in the emergence of the MVC pattern as a very popular choice to provide a solution.

One of the first widely used applications of the MVC pattern on web applications appeared as part of the Java Server Pages (JSP) specification, known as Model 2 [2, 10]. Model 2 implements MVC in Java using Servlets, Java Beans, and JSPs. Model 2 is perhaps the most popular implementation of the MVC pattern currently in use.

Another very popular Java implementation of the MVC pattern is the open source project Apache Struts. Struts provides the necessary framework to write web applications in Java following the MCV design pattern [1] using Java Server Pages (JSP) and Java Servlets as the main building blocks. The Struts framework has been in wide use since 2001 when the Jakarta project gained popularity [18].

Following the Java implementations came Microsoft's MVC versions for the Active Server Pages platform [16]. Initially MVC was proposed as part of the Microsoft Enterprise Library. The enterprise library is a set of suggested best practices along with standard code targeted to .NET Framework developers. Recently Microsoft has turned its MVC implementation into a full-fledged product, integral part of the latest version of ASP.NET and Visual Studio .NET [3].

Currently one of the most popular implementations of MVC can be found as part of the Rails framework for web-based development using Ruby. MVC is at the heart of Ruby on Rails and its principles determine how web applications written in the framework are structured [14]. Ruby on Rails is one of the factors that has largely contributed to the popularity of the Ruby language.

Benefits and Applications

• The main benefit of the MVC pattern is that it separates the data, application, and presentation logic from each other. Applications built following the MVC pattern result in an implementation that is more cohesive and less coupled. The essential functionality needed for an application's functionality is located in distinct components that specialize in one of the three core functions.

• The MVC pattern is an ideal choice for structuring web applications, where high interactivity is expected. MVC is particularly useful in applications where the same data must be presented in different ways. An example of this is a web-based catalog that offers a different interface for a desktop web browser and a more streamlined version for a browser used on mobile devices.

• Additional benefits of the MVC pattern include:
  • Applications that have a cleaner design. Key functionality is found in well known and clearly-defined components.
  • Increased code reuse and code that is easier to maintain.
  • The MVC pattern prevents the creation of monolithic applications where there is no separation of concerns.
  • Less coupling between application components.
  • Makes it easier to support multiple browser platforms, e.g. an application can be targeted to both desktop web browsers and mobile devices with the use of different views.
  • Simplifies the process of providing different types of interfaces to the same functionality.
  • More productive use of programming resources due to specialization. Some members of the team can focus on the data and business logic component (model) while others focus on the graphical user interface (view). Developer team responsibilities can be distributed to better match the capabilities of the team members, e.g. GUI experts can focus on producing an appealing and user-friendly interface without having to worry about data retrieval or navigation flow code.

Different Implementations

Many frameworks have been created to help in the implementation of the MVC pattern. The existing frameworks span multiple programming languages and platforms. The following table shows a list of different application development frameworks that implement the MVC pattern or are based on it. The table is not all-inclusive but the most popular frameworks are listed.

Implementation	Language	Platform	Description
Ruby on Rails	Ruby	Multiple, including Linux, Mac OS, Windows.	An open-source framework used to create Ruby-based web applications that follow the MVC pattern.
Apache Struts	Java	Multiple	An open-source implementation of the Model 2 specification. Uses Java Server Pages and Java Beans to implement web applications that follow the MVC pattern.
ASP.NET MVC	C#, VB.NET	Windows	A Microsoft product for the development of web applications that follow the MVC pattern. Currently a there is no cost for using ASP.NET MVC.
WebObjects	Java	Mac OS	A set of tools offered by Apple Computer for the development of Java-based web applications.
JavaServer Faces	Java	Multiple	A J2EE standard for server-side user interfaces.
Service to Worker Pattern for J2EE applications.	Java	Multiple	Intended for Web-based desktop applications, i.e. applications with only one user [18].
Tapestry	Java	Multiple	Open-source framework for web applications in Java.
OpenMVC	Java, C#	Multiple, including Microsoft .NET	An open source framework with versions for both .NET and Java. OpenMVC uses five tiers to implement an architecture that is based on MVC. The five tiers are: the client, the presentation logic layer, the business logic layer, the data abstraction layer, and the database [6].
Maverick	Java, .NET, PHP	Multiple	Mainly for Java web development.
Model View Presenter (MVP)	C#, VB.NET	Windows	A pattern inspired by the MVC, widely used on applications written for ASP.NET.

Resources

Ruby Programming Language

Rails

Java

Apache Struts

ASP.NET

ASP.NET MVC

Martin Fowler - Patterns in Enterprise Software

References

[1] Apache Struts Web Application Framework. 2009, http://struts.apache.org/.

[2] Designing Enterprise Applications with the J2EE Platform, Second Edition. 2009, http://java.sun.com/blueprints/guidelines/designing_enterprise_applications_2e/web-tier/web-tier5.html.

[3] ASP.NET MVC : The Official Microsoft ASP.NET Site. 2009, http://www.asp.net/mvc/.

[4] JavaServer Faces Technology. 2009, http://java.sun.com/javaee/javaserverfaces/.

[5] Developer - WebObjects. 2009, http://developer.apple.com/WebObjects/.

[6] BARRETT, R. AND DELANY, S.J. 2004. OpenMVC: a non-proprietry component-based framework for web applications. In WWW Alt. '04: Proceedings of the 13th international World Wide Web conference on Alternate track papers & posters, New York, NY, USA, ACM, New York, NY, USA, 464-465.

[7] BURBECK, S. 1997. Applications Programming in Smalltalk-80(TM): How to use Model-View-Controller (MVC). 2009, http://st-www.cs.illinois.edu/users/smarch/st-docs/mvc.html.

[8] CURRY, E. AND GRACE, P. 2008. Flexible Self-Management Using the Model-View-Controller Pattern. IEEE Software 25, 84-90.

[9] FOWLER, M. 2006. GUI Architectures. http://www.martinfowler.com/eaaDev/uiArchs.html.

[10] FREEMAN, E., FREEMAN, E., SIERRA, K. AND BATES, B. 2004. Head First Design Patterns. O'Reilly Media, Inc.

[11] GAMMA, E. 1995. Design patterns: elements of reusable object-oriented software Addison-Wesley, Reading, Mass.

[12] HANSEN, S. AND FOSSUM, T.V. 2005. Refactoring model-view-controller. J.Comput.Small Coll. 21, 120-129.

[13] KRASNER, G.E. AND POPE, S.T. 1998. A Description of the Model-View-Controller User Interface Paradigm in the Small-talk-80 System. 1, 26-49.

[14] SAM RUBY, THOMAS, D. AND DAVID HEINEMEIER HANSSON. Agile Web Development with Rails Pragmatic Bookshelf, .

[15] SKRIEN, D.J. 2009. The Model-View-Controller Architecture. In Object-Oriented Design Using Java, McGraw-Hill Higher Education, , 234.

[16] WALTHER, S. ASP.NET MVC Framework Unleashed. Sams, .

[17] WALTHER, S. 2008. The Evolution of MVC. .

[18] YAN, N., LEIP, D. AND GUPTA, K. 2005. The use of open-source software in the IBM corporate portal. IBM Systems Journal 44, 419-425.

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CSC 517 Fall 2009

Wiki 1b Assignment

Author: Newwolf