Overview of some newer web applications methods
• Web 2.0
• Ajax fundamentals
• Ruby on Rails
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 Software Architectures
 Larger organization of components
 Frameworks include:

Components we’re given as building blocks
 Standard forms of behavior between components
 Some frameworks for web-based applications
 AJAX and supporting frameworks
 Ruby on Rails
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 Client/Server architectures
 Web interface through the browser
 Client-side processing (Javascript)
 Server needs
 Underlying database management
 Server side processing
 Security, authorization, etc.

Transaction processing
 Business logic
 Etc.
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 Have a look at:
 Ajax: A New Approach to Web Applications, by Jesse
James Garrett http://www.adaptivepath.com/publications/essays/archives/000385.php
 Building Rich Web Applications with Ajax, by Linda
Dailey Paulson. (From IEEE Software .) http://www.computer.org/portal/cms_docs_ieeecs/ieeecs/images/ajax.pdf
 Book: Pragmatic Ajax: A Web 2.0 Primer (Overview)
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 Interact with a page
 Maybe enter info in forms, then hit Submit
 Server receives the URL (and forms data etc.)

Processes information, and then…
 New page is returned to the browser and loaded
 Even small changes require entire page to be reloaded
 (The web as a hypertext system, not a SW app platform)
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 Web 2.0: just a buzzword?
 See Wikipedia for the history
 In part, Web 2.0 is about
 The web as a computing platform
 But also:

“new generation” of web usage
 Collaboration, sharing, things linked together
 Examples (?):
 Blogs, social networking, Flickr, del.icio.us, Skype, games,
SecondLife, wikis, podcasts, RSS,…
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 Ajax

Named from “Asynchronous JavaScript and XML”
 Used to refer to two things

Collection of “old” Web-related technologies
 A web-based SW architecture
 Example apps: Google maps; new Yahoo mail
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 Presentation with XHTML and CSS
 Dynamic page display and interaction using the
DOM (Document Object Model) in the browser
 Data interchange and processing with XML and
XSLT
 Asynchronous data retrieval with
XMLHttpRequest (or equivalent)
 JavaScript
 Ties it all together on the client-side
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 Small events
 Small request to the server that makes small change to the page
 No refresh of complete page!
 Asynchronous processing

Browser doesn’t block while waiting
 Key is a XMLHttpRequest (Javascript to server)
 Richer events on the client-side
 Browser recognizes and shares events much like a
GUI-application does
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 from Garrett’s web article
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

From Pragmatic Ajax
See explanation given in class
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1.
2.
3.
4.
5.
6.
Browser requests original page
Servers sends back complete page
Browser displays and creates a DOM tree
(later) Some user activity initiates a request to the server
 Asynchronous! To a different URL for a script
Server returns data to browser to be handled differently than in (3) above
Browser process server-response and updates current DOM in memory
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 On the client side with JavaScript
 An object of type XMLHttpRequest (XHR for short)
 On the server side

Most basic: any kind of script like those you’ve written before
 More complex and useful: a larger framework
 E.g. servlets, Ruby on Rails, etc.

 Get request (with parameters) and send back data
(not a webpage)
 Simple, or more complex (XML)
Note that browsers must be “smarter” too
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
What’s it need to do?
 Be created and used by some JavaScript function
 Create a request to a script on the server
 E.g. a URL with parameters
 Send it
 Be linked to a call-back function that will be run on the client when the data is returned
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 From the demo (simplified) var xhr = XMLHttpRequest(); // not for older IE xhr.onreadystatechange= callback-func-name ; xhr.open(“GET”, “/ scriptURL ?” + param ); xhr.send(null);
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 Server talks to the call-back function multiple times

 xhr.readystate -- an int that indicates status
Value of 4 means it’s done and data is ready
 Also, xhr.status is set to HTTP response code


E.g. 404 “not found”.
200 means “OK”
 In call-back function, after checking the above:
 Get data sent back: xhr.responseText (text data)
 Process it and update current page using DOM

No reload of entire page occurs!
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 http://people.virginia.edu/~tbh3f/cs453/ajax1/
 Two very simple demos of XMLHttpRequest processing with JavaScript
 Very simple server-side processing with PHP
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 Serverside “remoting”
 Frameworks and toolkits to support communications more easily
 Client-side
 GUI toolkits for Ajax apps (Java Script)
 More complete toolkits for building larger apps

Rails, Tapestry, Dojo, Django, …
 SEAS Final 4 Bracket Challenge
 Aptana, includes support for Ajax/Javascript libraries

Used Dojo and Yahoo UI
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 Many frameworks use Ajax and provide
 Higher-level support for requests and responses
 Data integration between DBs on the server and client-side objects
 GUI support


Separation of data, control, presentation, business rules
“components” or “helpers”: sessions, carts, etc.
 Internationalization
 PHP users:
 Check out symfony
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 A framework for developing web apps
 Remember what a framework is?
 Rails derived from a real commercial application
 Features
 client-side dynamic pages (DHTML)
 good integration with database on the server
 coding written in Ruby
 based on the MVC architecture
 AJAX characteristics
 Book: Agile Web Development with Rails
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 More slogans!

DRY: Don’t repeat yourself

Things defined in code in one place only
 Convention over Configuration
 Code less by submitting to defaults
 Often depends on naming conventions
 Can override these if needed
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 Challenge: putting together an OO program with class design and a set of database tables
 ORM: object-relational mapping
 Rails version of ORM called Active Record
 Define class and get both Ruby class and DB table
 Get certain methods for free
 Other parts of the architecture rely on naming conventions etc. to make all work together with far less programming effort
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 MVC is a design pattern for interactive applications
 Model: just like in Observer
 Also enforces business rules
 View: displays the user-interface
 Controller
 receives external events from the user etc.
 interact with model and view
 Many other frameworks also use MVC
 E.g. Struts, JavaServer Faces
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(from book Agile Web Development with Rails)
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
First step: Rails code generation…
 Views:
 You write HTML pages with embedded Ruby
 Your code interacts with the controller
 Controller:
 You write code focused on application-specific functions
 Rails provides
 routing events/requests from pages/views to your handlers
 sessions, caching, …
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 The high-level big picture here is:

Certain kinds of applications…


(E.g. web-applications, DB-centered, etc.)
… benefit from particular architecture models…

 (E.g. Ajax ideas)
… and we use frameworks at the architecture level…


 (E.g. Rails or AJAX environments)
… and lower-level design and coding “tools”

(E.g. specific IDEs, toolkits, GUI libraries,…)
… to build larger, better systems quicker.
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