Web 2.0 Patterns and Technologies - Lecture 07 - Web Information Systems (4011474FNR)

2 December 2005
Web Information Systems
Web 2.0 Patterns and Technologies
Prof. Beat Signer
Department of Computer Science
Vrije Universiteit Brussel
http://www.beatsigner.com

Beat Signer - Department of Computer Science - bsigner@vub.ac.be 2November 14, 2014
The Programmable Web
 Based on HTTP
 Data often encoded in XML
 Potential alternative data formats
 HTML
 plain text
 JavaScript Object Notation (JSON)
 binary formats

Rich Internet Applications (RIAs)
 Bring the desktop to the browser
 Highly responsive (good performance)
 asynchronous and partial content updates
 Rich Graphical User Interface (GUI)
 various RIA toolkits and environments introduced earlier
- Adobe Flash, Apache Flex and AIR
- Microsoft Silverlight
- Sun JavaFX
- JavaServer Faces (JSF)
- Mozilla XUL (XML User Interface Language)
- OpenLaszlo
- ...

Asynchronous Partial Updates
Client Server
 Rather than updating an entire resource (e.g. webpage),
we can asynchronously update parts of a resource
 Updates initiated by the client (or the server) based on
user interaction, state change, timeout, …
Service Service

Asynchronous Partial Updates …
 Updates cannot be initiated by the server if HTTP is used!
 have to use polling or long polling (e.g. Comet model)
 There are different possibilities how the partial update of
resources can be realised over the Web
 AJAX
 Action Message Format (AMF)
- used by Apache Flex
 REST-based implementations
 …

AJAX
 Asynchronous JavaScript and XML
 AJAX is not a technology by itself but a group
of existing technologies (term coined in 2005)
 HTML and CSS for the visualisation
 JavaScript in combination with DOM to dynamically change the
presented information and process messages on the client side
 method to asynchronously exchange data between the client
(browser) and the server
- often via the XMLHttpRequest (XHR) JavaScript object
- data can be in different formats including XML, plain text, JavaScript Object
Notation (JSON), ...
 client-side AJAX engine deals with asynchronous message
handling

XMLHttpRequest Object
 The XMLHttpRequest (XHR) object has several
important properties
 onreadystatechange
- registers a JavaScript function that will handle the response from the server
 readyState
- represents a response status from the server
• 0 (unititialised): object has been created but is uninitialised
• 1 (open): object has been created but send method not yet called
• 2 (sent): send method has been called and the HTTP response headers have been received
• 3 (receiving): some data (body) has been received but response not yet available
• 4 (loaded): all data has been received and the response is available
- a function registered via onreadystatechage is executed each time readyState changes
 responseText, responseBody and responseXML
- contains the server's response in different formats

AJAX Example
<html>
<body>
<script type="text/javascript">
function createXMLHttpRequest() {
if (typeof XMLHttpRequest != "undefined") {
return new XMLHttpRequest();
}
else if (typeof ActiveXObject != "undefined") { // code for IE5 and IE6
return new ActiveXObject("Microsoft.XMLHTTP");
}
else {
throw new Error("XMLHttpRequest object not supported!")
}
}
function getTime() {
xhr = createXMLHttpRequest();
xhr.onreadystatechange=function() {
if (xhr.readyState == 4 && xhr.status == 200) {
document.testForm.time.value=xhr.responseText;
}
}
xhr.open("GET","time.php",true);
xhr.send(null);
}
</script>

AJAX Example ...
 createXMLHttpRequest() deals with different browser
versions
 For more advanced AJAX examples see
 http://www.w3schools.com/Ajax/
 Getting Started with Ajax
 http://refcardz.dzone.com/refcardz/
getting-started-ajax
<form name="testForm">
Input: <input type="text" name="input" onkeyup="getTime();" />
Time: <input type="text" name="time" />
</form>
</body>
</html>

Google Search (Suggest) AJAX Example

AJAX
 Advantages
 reduced load time and higher responsiveness
 application state can be maintained across multiple pages since
the main container page is not reloaded
 Disadvantages
 not possible to bookmark any particular state of an application
 content may not be crawled by certain search engines since they
do not execute JavaScript code
 cannot be used in browsers with disabled JavaScript functionality
 page updates are not automatically registered in the browser's
history engine
 Various libraries simplify the AJAX development
 e.g. the jQuery JavaScript library

Web Socket API
 Bidirectional, full-duplex socket connection between
the server and browser for real-time web applications
(low latency) with asynchronous partial updates
 server-initiated updates become possible!
 client and server upgrade from the HTTP protocol to the
WebSocket protocol (initial HTTP handshake)
- via Upgrade: websocket HTTP header field
- browser as well as server have to support the Web Socket protocol
 reduced "overhead" since no HTTP headers
 no longer necessary to do any polling or long polling
- faster since in the polling approach the server can send nothing while a client
request is transmitted
 similarly an EventSource object can be used if only the server
has to push information (server-sent events)
W3CCandidateRecommendation

Web Socket API ...
<script type="text/javascript">
var socket = new WebSocket("ws://chat-server.com");
socket.onopen = function(e) { alert("Opened connection ..."); };
socket.onmessage = function(e) {
var message = JSON.parse(e.data));
alert("Message received.");
...
};
socket.onclose = function(e) { alert("Closed connection."); };
socket.onerror = function(e) { alert("WebSocket Error" + e); };
socket.send("Hellow World");
...
socket.close();
</script>
W3CCandidateRecommendation

Web Sockets Support
When can I use..., http://caniuse.com/#search=socket

Example: Multiplayer Port of Quake II
 Google's browser port of Quake II uses
 canvas and WebGL
 <audio> for sound
 <video> for in-game videos
 Web Sockets for communication with the server (other players)
 Local Storage for managing preferences and saved games

JavaScript Object Notation (JSON)
 Developed as an XML alternative to represent JavaScript
objects as strings (language independent)
 Easy to produce and faster to parse than XML
 supports different data types
 JSON is based on a subset of JavaScript
 JSON document can be read via the JavaScript eval() function
- security issues: note that this approach can be dangerous if the source is not
trusted since any JavaScript code might be executed
 most recent browsers offer a JSON parser
- recognises only JSON data types and rejects any scripts
 Many Web 2.0 Applications offer a JSON interface
 Flickr, YouTube, Delicious, ...

JSON Data Types
 The values themselves can be simple values (number,
boolean or string), arrays or objects
 nesting is supported
Type Description
Number integer, real or float
Boolean true or false
String double-quoted Unicode (use backslash for escaping)
Array comma-separated ordered sequence of values enclosed in
square brackets
Object comma-separated collection of key:value pairs enclosed in
curly brackets
null null value

JSON Syntax Diagrams
http://www.json.org

JSON Example
{
"surname": "Signer",
"forename": "Beat",
"address": {
"street": "Pleinlaan 2",
"city": "Brussels",
"postalCode": 1050,
"country": "Belgium"
},
"phoneNumbers": [
{ "type": "office", "number": "123 456 789" },
{ "type": "fax", "number": "987 654 321" }
]
}

JSON-RPC
 Simple JSON-encoded remote procedure call protocol
that is very similar to XML-RPC (discussed earlier)
 multiple requests might be sent to a peer and answered out of
order (use id to match a request with its response)
{
"version": "1.1",
"method": "Math.multiply",
"id": "24034824",
"params": [128.0, 256.0]
}
JSON-RPC Request
{
"version": "1.1",
"result": 32768.0,
"error": null,
"id": "24034824"
}
JSON-RPC Response

Service-Oriented Architecture (SOA)
 Architecture that modularises functionality as
interoperable services
 loose coupling of services
 service encapsulation
 interoperability between different operating systems and
programming languages
 mashup of services
 ...
 Software as a service (SaaS)
 software is offered as a service and may itself be a composition of
third-party services

Representational State Transfer (REST)
 REST is an architectural style for distributed hypermedia
systems requirering the following constraints
(1) separation of concerns between client and server
 client and server can be developed and replaced independently
(2) uniform interface
 identification of resources (e.g. URIs on the Web)
 manipulation of resources on the server via representation on the client side
 self-describing messages (e.g. MIME type on the Web)
 hypermedia for application state change (e.g. hypertext links to related
resources)
(3) stateless
 no client state is stored on the server side
(4) cacheability
 responses must explicitly or implicitly define whether they are cacheable

Representational State Transfer (REST) ...
(5) layering
 intermediary servers (proxies) can be transparently added between the client
and the server
(6) code on demand (optional)
 the server can send application logic (code) to the client (e.g. Java Applets)
 A service that conforms at least to the first five
constraints is called a RESTful service
 The Web is an implementation of a system conforming to
the REST architectural style
 however, RESTful services can also be implemented over
protocols other than HTTP

Web Services
 Web-based client-server communication
over HTTP
 Two main types of Web Services
 Big Web Services
- Universal Description, Discovery and Integration (UDDI)
- Web Services Description Language (WSDL)
- Simple Object Access Protocol (SOAP)
 RESTful Web Services
- better integrated with HTTP and web browsers
- makes use of GET, POST, PUT and DELETE HTTP methods

Big Web Services
Service
Provider
Service
Requester
Service
Broker
UDDI
WSDL
SOAP
SOAP
WSDL

Big Web Services ...
 Universal Description, Discovery and Integration (UDDI)
 yellow pages for WSDL
 "global" registry describing available business services
 very complex
 Microsoft and IBM shut down their public UDDI registries in 2006
 Web Service Description Language (WSDL)
 XML application to describe a Web Service's functionality
 complex
 Simple Object Access Protocol (SOAP)
 defines an envelope for transporting XML messages
 The Web Service Stack contains many other protocols
 BPEL, WS-Security, WS-Reliability, WS-Transaction, ...

SOAP
 Successor of XML-RPC (discussed earlier)
 Introduced in 1998 as Simple Object Access Protocol
 Dave Winer, Don Box, Bob Atkinson and Mohsen Al-Ghosein
 since version 1.2 the name is no longer treated as an acronym
 XML-based communication protocol
 A SOAP message consists of an <Envelope> element
which contains
 an optional <Header> element
 a <Body> element
- remote procedure call or response information
 SOAP requests are often sent via HTTP POST requests

SOAP Request Message Example
 predefined SOAP attributes
- encodingStyle: defines the used data types
- mustUnderstand: if set to 1 then the server has to understand the header
- actor: can be used to delegate the header to an intermediary receiver (proxy)
<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">
<soap:Header>
<t:username xmlns:t="http://wise.vub.ac.be/transaction/"
soap:mustUnderstand="1">pellens</t:username>
</soap:Header>
<soap:Body xmlns:c="http://wise.vub.ac.be/courses/">
<c:getCourseInfo>
<c:courseID>4011474FNR</c:courseID>
</c:getCourseInfo>
</soap:Body>
</soap:Envelope>

SOAP Response Message Example
 note that also a response message can have a <Header> element
 the body contains a <Fault> element if something went wrong on
the server side
<soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">
<soap:Body>
<c:getCourseInfoResponse xmlns:c="http://wise.vub.ac.be/courses">
<c:title>Web Information Systems</c:title>
<c:description>The goal of this course is to teach students the concepts and
technologies for realising Web Information Systems (WIS). This ranges from basic
network technologies and protocols to high level frameworks for the design and
...
</c:description>
</c:getCourseInfoResponse>
</soap:Body>
</soap:Envelope>

SOAP ...
 Advantages
 platform and language independent
 SOAP over HTTP results in less problems with proxies and
firewalls than other remote procedure call solutions (e.g. CORBA)
 there exist a lot of tools and language bindings that automatically
create the required client and server-side functionality
- e.g. Java API for XML Web Services (JAX-WS)
 Disadvantages
 slower than non-verbose protocols (e.g. CORBA)
 Big Web Services are not simple
 HTTP is reduced to a simple transport protocol for a large amount
of XML metadata payload
- does not make use of the rich functionality offered for HTTP envelopes
 no mechanism for the caching of results

RESTful Web Services
 A RESTful web service (or RESTful Web API) is a simple
web service implemented using HTTP
 The definition of RESTful web service includes
 the URI of the web service (e.g. http://wise.vub.be/course/)
- different resources identified by unique URIs
 the type (MIME) of data supported by the service
- e.g. application/json, application/xml, ...
 supported set of operations via HTTP methods
- e.g. GET, POST, PUT, DELETE
 One-to-one mapping between create, read, update, and
delete (CRUD) operations and HTTP methods
 POST (create), GET (read), PUT (update) and DELETE (delete)

RESTful Web Service Example
POST /users HTTP/1.1
Host: wise.vub.ac.be
Content-Type: application/xml
<user>
<name>Roels</name>
</user> create
GET /users/Roels HTTP/1.1
Accept: application/xml read
PUT /users/Roels HTTP/1.1
Content-Type: application/xml
<user>
<name>Signer</name>
</user> update
DELETE /users/Signer HTTP/1.1
Accept: application/xml delete

Apache CouchDB
 Document-oriented database
 provides a RESTful JSON API
- manage the database by simply using POST, GET, PUT and DELETE HTTP
requests with JSON payload
 non-relational database
- manages a collection of JSON documents
 free and open source
 Implemented in Erlang
 functional programming language that is ideal for building
concurrent distributed systems
 leads to a flexible CouchDB design that is scalable and extensible
 Nice example of a RESTful web service that can easily
be accessed from various types of clients

Really Simple Syndication (RSS)
 Format that is used to read and write frequently updated
information on the Web
 e.g. blog entries
 specific channels on news sites
 ...
 Special RSS readers or aggregators
 Two main RSS variants
 simple fork (Dave Winer)
- RSS 0.92, RSS 0.93, RSS 0.94 and RSS 2.0
 RDF fork
- RSS 1.0
 RSS feeds are represented as XML documents

RSS Example
 many other elements
 <language>, <copyright>, <pubDate>, ...
<?xml version="1.0" encoding="ISO-8859-1" ?>
<rss version="2.0">
<channel>
<title>W3Schools Home Page</title>
<link>http://www.w3schools.com</link>
<description>Free web building tutorials</description>
<item>
<title>RSS Tutorial</title>
<link>http://www.w3schools.com/rss</link>
<description>New RSS tutorial on W3Schools</description>
</item>
<item>
<title>XML Tutorial</title>
<link>http://www.w3schools.com/xml</link>
<description>New XML tutorial on W3Schools</description>
</item>
...
</channel>
...
</rss>

Atom
 Two related standards
 Atom Syndication Format
- similar to RSS
- supports more content formats (e.g. videos) than RSS
 Atom Publishing Protocol (APP)
- HTTP-based approach for creating and editing Web resources
- similar to the RESTful web service example shown earlier
 Many web service interfaces are based on
the Atom protocol
 Microsoft Windows Live
 OpenSocial
 …

Mashups
 Combine content or functionality from existing
websites, web services and RSS feeds
 different mashup tools may address different types
of users (e.g. developers vs. end users)
 Various Mashup tools
 Yahoo Pipes
 IBM Mashup Center
 ...

Video: Yahoo Pipes
Creating a basic pipe, http://blip.tv/file/get/Jc174-YahooPipesBasics201.wmv

Video: Yahoo Pipes ...
Sorting, filtering, and debugging, http://blip.tv/file/get/Jc174-YahooPipesSortingFilteringAndDebugging584.wmv

Video: Yahoo Pipes ...
Using other People’s Pipes, http://blip.tv/file/get/Jc174-YahooPipesTheYahooSearchModuleUnionModuleAndUsingOther879.wmv

Exercise 7
 Mashup Tools

References
 AJAX Tutorial
 http://www.w3schools.com/Ajax/
 Mike Amundsen, Building Hypermedia APIs with HTML5
& Node, O'Reilly Media, December 2011
 Jim Webber, Savas Parastatidis and Ian Robinson, REST
in Practice: Hypermedia and Systems Architecture,
O'Reilly Media, September 2010
 Dave Crane, Getting Started with Ajax
 http://refcardz.dzone.com/refcardz/getting-started-
ajax

References ...
 jQuery Cross-Browser JavaScript library
 http://jquery.com
 JSON Syntax Diagrams
 http://www.json.org
 Brian Sletten, REST: Foundations of RESTful
Architecture
 http://refcardz.dzone.com/refcardz/rest-foundations-
restful
 W3C Web Services Activity
 http://www.w3.org/2002/ws/
 Apache CouchDB
 http://couchdb.apache.org

References ...
 Dave Johnson, RSS and Atom
 http://refcardz.dzone.com/refcardz/rss-and-atom
 Yahoo Pipes Tutorial
 http://usefulvideo.blogspot.com/2007/02/yahoo-pipes-
tutorials.html

2 December 2005
Next Lecture
Mobile Information Systems

Web 2.0 Patterns and Technologies - Lecture 07 - Web Information Systems (4011474FNR)

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