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A web application framework is a software framework that is designed to support the development of dynamic websites, web applications and web services. The framework aims to alleviate the overhead associated with common activities performed in Web development. For example, many frameworks provide libraries for database access, templating frameworks and session management, and they often promote code reuse.^[1] For a comparison of concrete web application frameworks, confer Comparison of web application frameworks.

History

Template:Histinfo As the design of the World Wide Web was not inherently dynamic, early hypertext consisted of hand-coded HTML that was published on web servers. Any modifications to published pages needed to be performed by the pages' author. To provide a dynamic web page that reflected user inputs, the Common Gateway Interface (CGI) standard was introduced for interfacing external applications with web servers.^[2] CGI could adversely affect server load, though, since each request had to start a separate process.

Programmers wanted tighter integration with the web server to enable high traffic web applications. The Apache HTTP Server, for example, supports modules that can extend the web server with arbitrary code executions (such as mod perl) or forward specific requests to a web server that can handle dynamic content (such as mod jk). Some web servers (such as Apache Tomcat) were specifically designed to handle dynamic content by executing code written in some languages, such as Java.

Around the same time, new languages were being developed specifically for use in the web, such as ColdFusion, PHP and Active Server Pages.

While the vast majority of languages available to programmers to use in creating dynamic web pages have libraries to help with common tasks, web applications often require specific libraries that are useful in web applications, such as creating HTML (for example, JavaServer Faces).

Eventually, mature, "full stack" frameworks appeared, that often gathered multiple libraries useful for web development into a single cohesive software stack for web developers to use. Examples of this include ASP.NET, JavaEE (Servlets), WebObjects, web2py, OpenACS, Catalyst, Mojolicious, Ruby on Rails, Django, Zend Framework and Symfony.

Types of frameworks

Most web application frameworks are based on the model–view–controller (MVC) pattern.

Model–view–controller (MVC)

Many frameworks follow the model–view–controller (MVC) architectural pattern to separate the data model with business rules from the user interface. This is generally considered a good practice as it modularizes code, promotes code reuse, and allows multiple interfaces to be applied. In Web applications, this permits different views to be presented, such as web pages for humans, and web service interfaces for remote applications.

Push-based vs. pull-based

Most MVC frameworks follow a push-based architecture also called "action-based". These frameworks use actions that do the required processing, and then "push" the data to the view layer to render the results.^[3] Struts, Django, Ruby on Rails, Symfony, Yii, Spring MVC, Stripes, and Struts2^[4] are good examples of this architecture. An alternative to this is pull-based architecture, sometimes also called "component-based". These frameworks start with the view layer, which can then "pull" results from multiple controllers as needed. In this architecture, multiple controllers can be involved with a single view. Play, Lift, Tapestry, JBoss Seam, and Wicket are examples of pull-based architectures.

Three-tier organization

In Three Tier Organization, applications are structured around three physical tiers: client, application, and database.^[5]^[6]^[7]^[8] The database is normally an RDBMS. The Application contains the business logic, running on a server and communicates with the client using HTTP.^[9] The client, on web applications is a web browser that runs HTML generated by the application layer.^[10]^[11] The term must not be confused with MVC. Unlike in three-tier architecture, it is considered a good practice to keep business logic away from the controller, the "middle layer" in MVC.^[12]^[13]

Content management systems

Some projects that have historically been termed content management systems have begun to take on the roles of higher-layer Web application frameworks. For instance, Drupal's structure provides a minimal core whose function is extended through modules that provide functions generally associated with web application frameworks. The Joomla platform provides a set of APIs to build Web and command-line applications. However, it is debatable whether "management of content" is the primary value of such systems, especially when some, like SilverStripe, provide an object-oriented MVC framework. Add-on modules now enable these systems to function as full-fledged applications beyond the scope of content management. They may provide functional APIs, functional frameworks, coding standards, and many of the functions traditionally associated with Web application frameworks.

Features

Web template system

Dynamic web pages usually consist of a static part (HTML) and a dynamic part, which is code that generates HTML. The code that generates the HTML can do this based on variables in a template, or on code. The text to be generated can come from a database, thereby making it possible to dramatically reduce the number of pages in a site.

Consider the example of a real estate agent with 500 houses for sale. In a static web site, the agent would have to create 500 web pages in order to make the information available. In a dynamic website, the agent could potentially connect a single dynamic web page to a database table of 500 records.

In a template, variables from the programming language can be inserted without using code, thereby losing the requirement of programming knowledge to make updates to the pages in a web site. A syntax is made available to distinguish between HTML and variables. E.g. in JSP the <c:out> tag is used to output variables, and in Smarty, {$variable} is used.

Many template engines do support limited logic tags, like IF and FOREACH. These are to be used only for decisions that need to be made for the presentation layer, in order to keep a clean separation from the business logic layer, or the M(odel) in the MVC pattern.

Caching

Web caching is the caching of web documents in order to reduce bandwidth usage, server load, and perceived "lag". A web cache stores copies of documents passing through it; subsequent requests may be satisfied from the cache if certain conditions are met. Some application frameworks provide mechanisms for caching documents and bypassing various stages of the page's preparation, such as database access or template interpretation.

Security

Some web application frameworks come with authentication and authorization frameworks, that enable the web server to identify the users of the application, and restrict access to functions based on some defined criteria. Drupal is one example that provides role-based access to pages, and provides a web-based interface for creating users and assigning them roles.

Database access, mapping and configuration

Many web application frameworks create a unified API to a database backend, enabling web applications to work with a variety of databases with no code changes, and allowing programmers to work with higher-level concepts. For higher performance, database connections should be pooled as e.g. AOLserver does. Additionally, some object-oriented frameworks contain mapping tools to provide Object-Relational Mapping, which will map objects to tuples.

Some frameworks minimize web application configuration through the use of introspection and/or following known conventions. For example, many Java frameworks use Hibernate as a persistence layer, which can generate a database schema at runtime capable of persisting the necessary information. This allows the application designer to design business objects without needing to explicitly define a database schema. Frameworks such as Ruby on Rails can also work in reverse, that is, define properties of model objects at runtime based on a database schema.

Other features web application frameworks may provide include transactional support and database migration tools.

Scaffolding

Some model-view-controller frameworks generate code that the application can use to create, read, update and delete database entries.

URL mapping

A framework's URL mapping facility is the mechanism by which the framework interprets URLs. Some frameworks, such as Drupal and Django, match the provided URL against pre-determined patterns using regular expressions, while some others use URL Rewriting to translate the provided URL into one that the underlying engine will recognize. Another technique is that of graph traversal such as used by Zope, where a URL is decomposed in steps that traverse an object graph (of models and views).

A URL mapping system that uses pattern matching or URL rewriting allows more "friendly" URLs to be used, increasing the simplicity of the site and allowing for better indexing by search engines. For example, a URL that ends with "/page.cgi?cat=science&topic=physics" could be changed to simply "/page/science/physics". This makes the URL easier to read and provides search engines with better information about the structural layout of the site. A graph traversal approach also tends to result in the creation of friendly URLs. A shorter URL such as "/page/science" tends to exist by default as that is simply a shorter form of the longer traversal to "/page/science/physics".

Ajax

Ajax, shorthand for "Asynchronous JavaScript and XML", is a web development technique for creating interactive web applications. The intent is to make web pages feel more responsive by exchanging small amounts of data with the server behind the scenes, so that the entire web page does not have to be reloaded each time the user requests a change. This is intended to increase the web page's interactivity, speed, and usability.

Due to the complexity of Ajax programming in Javascript, there are numerous Ajax frameworks that exclusively deal with Ajax support. Some Ajax frameworks are even embedded as a part of larger frameworks. For example, the jQuery JavaScript Library is included in Ruby on Rails.

With the increased interest in developing "Web 2.0" Rich Media Applications, the complexity of programming directly in Ajax and Javascript has become so apparent that compiler technology has stepped in, to allow developers to code in high-level languages such as Java, Python and Ruby. The first of these compilers was Morfik followed by Google Web Toolkit, with ports to Python and Ruby in the form of Pyjamas and RubyJS following some time after. These compilers and their associated widget set libraries make the development of Rich Media Ajax Applications much more akin to that of developing Desktop applications.

Web services

Some frameworks provide tools for creating and providing web services. These utilities may offer similar tools as the rest of the web application.

References

^ Multiple (wiki). "Web application framework". Docforge. Retrieved 2010-01-19.
^ "CGI: Common Gateway Interface". Retrieved 2007-07-29.
^ Thomson, Kris (2003-10-29). "Clarification on MVC Pull and MVC Push". Retrieved 2007-07-29.
^ http://struts.apache.org/2.2.1/docs/what-are-the-fundamental-differences-between-struts-and-jsf.html
^ Microsoft. "Three-tiered distribution". Retrieved 2011-09-19.
^ Oracle. "clustering_concepts_10en" (PDF). Retrieved 2011-09-19.
^ Robert R. Perkoski. [www.sis.pitt.edu/~perkoski/is1092/slides/chapter01.ppt "Introduction to Web Development"]. Retrieved 2011-09-19. {{cite web}}: Check |url= value (help)
^ IBM. "Using Client Access Express in a three tier environment". Retrieved 2011-09-19.
^ Oracle. "Understanding the Three-Tier Architecture". Retrieved 2011-09-19.
^ Microsoft. "Pragmatic Architecture: Layering". Retrieved 2011-09-19.
^ Arokia. "3-Tier Web Architecture". Retrieved 2011-09-19.
^ "ASP.NET MVC Controller Best Practices". Retrieved 2011-09-19.
^ Jamis Buck. "Skinny Controller, Fat Model". Retrieved 2011-09-19.

[1] Multiple (wiki). "Web application framework". Docforge. Retrieved 2010-01-19.

[2] "CGI: Common Gateway Interface". Retrieved 2007-07-29.

[3] Thomson, Kris (2003-10-29). "Clarification on MVC Pull and MVC Push". Retrieved 2007-07-29.

[4] ttp://struts.apache.org/2.2.1/docs/what-are-the-fundamental-differences-between-struts-and-jsf.html

[5] Microsoft. "Three-tiered distribution". Retrieved 2011-09-19.

[6] Oracle. "clustering_concepts_10en" (PDF). Retrieved 2011-09-19.

[7] Robert R. Perkoski. [www.sis.pitt.edu/~perkoski/is1092/slides/chapter01.ppt "Introduction to Web Development"]. Retrieved 2011-09-19. {{cite web}}: Check |url= value (help)

[8] IBM. "Using Client Access Express in a three tier environment". Retrieved 2011-09-19.

[9] Oracle. "Understanding the Three-Tier Architecture". Retrieved 2011-09-19.

[10] Microsoft. "Pragmatic Architecture: Layering". Retrieved 2011-09-19.

[11] Arokia. "3-Tier Web Architecture". Retrieved 2011-09-19.

[12] "ASP.NET MVC Controller Best Practices". Retrieved 2011-09-19.

[13] Jamis Buck. "Skinny Controller, Fat Model". Retrieved 2011-09-19.

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   | url=http://www.theserverside.com/patterns/thread.tss?thread_id=22143
   | date = 2003-10-29
-  | accessdate = 2007-07-29 }}</ref> [[Struts]], [[Django (web framework)|Django]], [[Ruby on Rails]], [[Symfony]], [[Yii]], [[Spring MVC]] and [[Struts2]]<ref>http://struts.apache.org/2.2.1/docs/what-are-the-fundamental-differences-between-struts-and-jsf.html</ref> are good examples of this architecture.  An alternative to this is pull-based architecture, sometimes also called "component-based". These frameworks start with the view layer, which can then "pull" results from multiple controllers as needed. In this architecture, multiple controllers can be involved with a single view. [[Play_Framework|Play]], [[Lift_(web_framework)|Lift]], [[Tapestry (programming)|Tapestry]], [[JBoss Seam]], [[Apache Wicket|Wicket]] and [[Stripes (framework)|Stripes]] are examples of pull-based architectures.
+  | accessdate = 2007-07-29 }}</ref> [[Struts]], [[Django (web framework)|Django]], [[Ruby on Rails]], [[Symfony]], [[Yii]], [[Spring MVC]], [[Stripes (framework)|Stripes]], and [[Struts2]]<ref>http://struts.apache.org/2.2.1/docs/what-are-the-fundamental-differences-between-struts-and-jsf.html</ref> are good examples of this architecture.  An alternative to this is pull-based architecture, sometimes also called "component-based". These frameworks start with the view layer, which can then "pull" results from multiple controllers as needed. In this architecture, multiple controllers can be involved with a single view. [[Play_Framework|Play]], [[Lift_(web_framework)|Lift]], [[Tapestry (programming)|Tapestry]], [[JBoss Seam]], and [[Apache Wicket|Wicket]] are examples of pull-based architectures.
 ===Three-tier organization===