Web Services

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Web Services

• Updated by Dr Suthikshn Kumar
• Suthikshn.kumar_at_pes.edu

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Contents

• What is WS?
• SOAP
• RPC style SOAP
• Document Style SOAP
• WSDL
• REST Services
• JSON Format
• What is JSON?
• Array Literals
• Object Literals
• Mixing Literals
• JSON Syntax
• JSON Encoding and Decoding
• JSON vs XML

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Introduction

• When XML use began to take off after 2000,
  businesses, developers, and others looked for new
  ways to use it.
• The promise of separating content and
  presentation had been met, but how could this
  capability be capitalized upon?
• The answer was web services.
• Web services provide a way to exchange data
  between applications and services.
• To facilitate this communication, web services
  use the internet to send messages composed of XML
  data back and forth between the consumer and
  provider.
• The major difference with web services is that
  the data being transmitted is XML text instead of
  a binary format.
• The promise behind web services is that of having
  software components available on demand, to any
  application in the world.
• Whether that be a web application or a
  traditional desktop application, it is possible
  to use the same service to perform the same task.

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Related Technologies

• SOAP( Simple Object Access Protocol) is a
  combination of an XML-based language and any
  number of common protocols for transmitting this
  data.
• WSDL Web Services Description Language is
  another XML based language that was created to
  describe the usage of a particular web service,
  or rather, how a particular service could be
  called.
• REST Representation State Transfer, describes
  of using the existing HTTP protocol to transmit
  data.

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Service Oriented Architecture

• Service-Oriented Architecture (SOA) expresses a
  software architectural concept that defines the
  use of services to support the requirements of
  software users

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Service Oriented Architecture
Service Provider
Service Requestor
Internet
Legacy System
Service Broker
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Requirements for a SOA

• Interoperability between different systems and
  programming languages
• Clear and unambiguous description language
• Retrieval of the service
• Security

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Web Services DefinitionW3C

• A Web service is a software system
• Identified by a URL, whose public interfaces and
  bindings are defined and described using XML.
• Its definition can be discovered by other
  software systems
• These systems may then interact with the Web
  service
• using XML based messages conveyed by Internet
  protocols
• Web Services implement a Service Oriented
  Architecture

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Web Services

• Web services are an emerging technology that
  offer a solution for providing a common
  collaborative architecture.
• Web services provide functional building blocks
  which are not tied to any particular programming
  language or hardware platform.
• They are accessible over standard Internet
  protocols.

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The Evolution

• Online systems replace Batch systems
• Graphical User Interfaces replace green screens
• Networked systems replace standalone systems
• Internet based systems replace LAN based systems
• Future ???
• Web Services replace simple Internet and LAN
  based systems

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Technologies

• XML (eXtensible Markup Language)
• markup language that underlies most of the
  specifications used for Web services.  
• SOAP (Simple Object Access Protocol)
• (Simple Object Access Protocol), similar to JDBC,
  is a network, transport, and programming language
  and platform neutral protocol that allows a
  client to call a remote service. The message
  format is XML.
• WSDL (Web services description language)
• An XML-based interface and implementation
  description language. The service provider uses a
  WSDL document in order to specify the operations
  a Web service provides. 
• UDDI (universal description, discovery, and
  integration)
• Both a client-side API and a SOAP-based server
  implementation that can be used to store and
  retrieve information on service providers and Web
  services.

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How it works

• A Web Service is a URL-addressable software
  resource that performs functions (or a function).
  
• Web Services communicate using standard protocol
  known as SOAP (Simple Object Access Protocol).
• A Web Service is located by its listing in a
  Universal Discovery, Description and Integration
  (UDDI) directory.

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Integration
What are Web Services good for?

• In a lot of organizations, the data and logic of
  one application are basically useless to other
  applications.
• When an application and its data are isolated
  from other applications, we often say that they
  are in silos.
• Web Services are better at sharing data and
  functions.
• The result is that the silos come down, and
  previously isolated systems can talk to each
  other.

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Access
What are they good for?

• Web Services are especially good at providing
  access through different interfaces.
• A Web Service can have a dedicated client
  application, but it can also be readily accessed
  through browsers, wireless devices,
  voice-activated interfaces, and so on.
• Adding new access methods is much simpler than
  with a traditional application.

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Flexibility
What are they good for?

• One of the more important innovations in Web
  Services is machine-to-machine communications.
• This means that a Web Service can ask another Web
  Service to do something, and that Web Service can
  ask another Web Service to do something, and so
  on.
• In the future, many Web Services will really just
  be aggregations of other Web Services.

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Application Assembly
What are they good for?

• Future applications will be assembled from a
  diverse group of web services, aggregating
  functionality.
• Reusability is extended to the execution level,
  versus reusability from just the design and
  construction level.

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SOAP

• Simple Object Access Protocol
• SOAP is an open protocol specification defining a
  uniform way of performing RPCs using HTTP as the
  underlying communications protocol with XML for
  the data serialization.

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SOAP

• The SOAP spec describes an intricate language
  with numerous elements and attributes, intended
  to describe most types of data.
• This information can be transported over any
  number of protocols, but is most commonly sent
  over HTTP along with other web traffic.
• There are two ways of using SOAP
• Remote procedure call style
• Document Style

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RPC-Style SOAP

• The RPC style of SOAP treats the web service as
  though it were an object containing one or more
  methods.
• A request is made to the service detailing the
  method name to call and the parameters if any to
  pass.
• The method is executed on the server and an XML
  response is dispatched containing the return
  value, if any.

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RPC-Style SOAP example

• A web service that provides simple arithmetic
  ops addition, subtraction, multiplication and
  division. Each method takes two numbers and
  returns a result.
• An RPC style request for the add operation would
  look like this
• lt?xml version 1.0 encoding utf-8 ?gt
• ltsoapEnvelope xmlnssoap http//schemas.xmlsoap
  .org/soap/envelope
• soapencodingStyle http//schemas.xmlsoap.org/s
  oap/encoding/gt
• ltsoapBodygt
• ltwadd xmlnsw http//www.wrox.com/services/mat
  h gt
• ltwop1gt4.5lt/wop1gt
• ltwop2gt5.4lt/wop2gt
• lt/waddgt
• lt/soapBodygt
• lt/soapEnvelopegt

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RPC-style SOAP response

• If the request to add two numbers executed
  successfully, the response message would look
  like
• lt?xml version 1.0 encoding utf-8 ?gt
• ltsoapEnvelope xmlnssoap http//schemas.xmlsoap
  .org/soap/envelope
• soapencodingStyle http//schemas.xmlsoap.org/s
  oap/encoding/gt
• ltsoapBodygt
• ltwaddReponse xmlnsw http//www.wrox.com/servic
  es/math gt
• ltwaddResultgt9.9lt/waddResultgt
• lt/waddResponsegt
• lt/soapBodygt
• lt/soapEnvelopegt
• If there were any problems processing the SOAP
  request on the server, then a ltsoapFaultgt
  element will be returned.

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Document-Style SOAP

• The document style of SOAP relies on XML schemas
  to designate the format of the request and
  response.
• This style seems to be gaining in poularity and
  some predict that it will eventually all but
  replace the RPC style.
• A document-style request may not look that
  different from an RPC-style request. ( simply
  remove the soapencodingStyle attribute)
• lt?xml version 1.0 encoding utf-8 ?gt
• ltsoapEnvelope xmlnssoap http//schemas.xmlsoap
  .org/soap/envelope gt
• ltsoapBodygt
• ltwadd xmlnsw http//www.wrox.com/services/mat
  h op1 4.5 op2 5.4 /gt
• lt/soapBodygt
• lt/soapEnvelopegt

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WSDL

• Web Services Description Language
• WSDL is XML-based language
• Was created to describe the usage of a particular
  web service, how a particular service could be
  called.
• The WSDL specification describes an incredibly
  dense language, designed to be extremely flexible
  and allow for as much re-use as possible.
• Typically, a software tool is used for the
  initial WSDL file creation and then hand tweaked
  as necessary.

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Difference between Document Style and RPC style
SOAP

• The Document Style sends the message as elements
  within the ltsoapbodygt that can have whatever
  structure the sender and receiver agree on using
  the embedded schema as a guide.
• An RPC-style message had an element named after
  the method being called. This in turn will have
  one element for each parameter the method
  accepts.

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REST ( Representation State Transfer)

• Describes a way of using the existing HTTP
  protocol to transmit data.
• REST can be used for any type of HTTP based
  request and response systems as well.
• With regard to web services, REST enables you to
  call a given URL in a specific format to return
  the data.

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REST example

• Wrox would like to provide a way for others to
  retriev a list of all authors. REST style web
  service use simple URLs to access data the wrox
  book service could use this URL to retrieve the
  list of authors
• http//www.wrox.com/services/authors
• This service may return an XML representation of
  the known authors along with information on how
  to access details about each one, such as
• lt?xml version 1.0 encoding utf-8 ?gt
• ltauthors xmlnsxlink http//www/w3.org/1999/xlink
  
• Xmlns http//www.wrox.com/services/authors-books
  
• Xlinkhrefhttp//www.wrox.com/services/authors/gt
• ltauthor forenames Michael surname kay
• xlinkhref http//www.wrox.com/services/authors/
  kaym
• id fawcettj /gt
• lt! More authors --- gt
• lt/authorsgt

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REST example contd

• Xlink is a way of linking documents that goes way
  beyond the straightforward hyperlinks in HTML. It
  provides capabilities to specify a two-way
  dependency so that documents can be accessible
  from each other as well as indicating how a link
  should be activated for exmaple by hand,
  automatically or after a preset time.
• If used in a web site or web application, the XML
  returned from the REST service would be
  transformed either client side or server-side to
  a more user-friendly format
• lthtmlgt
• ltheadgt
• lttitlegt Wrox Authors lt/titlegt
• lt/headgt
• ltbodygt
• lta href http//www.wrox.com/services/authors/kay
  mgtMichael Kaylt/agt
• lta href http//www.wrox.com/services/authors/faw
  cettjgtJoe Fawcettlt/agt
• lt/bodygt
• lt/htmlgt

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How Is a Service Described?

• WSDL (Web Service Description Language)
• XML-based
• Submitted to W3C for standardization
• Terraserver example
• httpterraserver.microsoft.com/default.aspx

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How Do I Find Web Services?

• UDDI project by Microsoft, IBM, and others. Take
  a look at //uddi.org
• Websites
• //www.xmethods.net
• //www.salcentral.com
• Commercial
• //www.serviceobjects.com
• //www.xmethods.net

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ServiceObjects
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FastWeather
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Using the FastWeather Web Service
ServiceObjectsWeb Service
RV Application
Internet
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WebSphere Studio Wizards

• Wizards make it easy for you to create and use
  Web Services
• Wizard to create a Web Service from a JavaBean
• Generates WSDL document
• Creates all required software components
• Create a Test client
• Wizard to create a Web Service Client
• Use the WSDL document as input

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Generate a Web Service Client
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Client Configuration
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Web Service Selection
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Web Service Client Test
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Testing
Input.jsp
Method.jsp
Result.jsp
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Web Service HTML File
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weather.html
ltIFRAME src"Input.jsp?method13" nameinput
scrolling"no" frameborder"0" align"top"
height"350"gt lt/IFRAMEgt ltIFRAME
src"Result.jsp" name"result" scrolling"no"
frameborder"0" align top height"350"gt
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weather.html
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Web Service as part of RV Application
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Lab Exercises

• Create Web Services client
• Integrate Web Service into the RV application

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JSON

• JSON - JavaScript Object Notation
• Tutorial of this simple and universal data
  exchange format
• JSON is a part of the ECMAScript standard since
  ECMA has defined in 1999 the eval() function that
  parses the format.It has been popularized with
  the success of Ajax. The JSON word appears often
  when one is speaking about Ajax. We know this is
  another data format, that can replace XML, and
  this format is supported by a lot of programmers.
  But what is exactly JSON, what are the
  advantages?
• Content
• Why JSON?
• JSON and XML
• The syntax of JSON
• Example of JSON file
• How to use the format
• Client side (browser)
• Server side
• Data exchange
• Example
• Simple demo
• YAML and JSON
• Resources

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Why JSON

• Why JSON?
• The benefit of JSON is that it is recognized
  natively by JavaScript. No need for parsing an
  XML document to extract the data and get it
  throught the net.
• JSON and XML
• Benefits of JSON - The easiness of reading.-
  The easiness of using.Benefits of XML- XML is
  extensible.- It is widely used and recognized by
  almost all programming languages. Unfortunally,
  both XML and JSON are enable to integrate a large
  amount of data in binary form.

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The syntax of JSON

• The components of JSON- An object contains
  objets or attributes.- A scalar variable
  Number, String, Boolean.- An array.- Literal
  values null, true, false, "string of
  characters", and numerical values.
• Object
• It contains a member or a list of members, and
  each member has the form
• "name" "value" The syntax of the object is
• member, member, .... Array
• A collection of values, separated by commas.
  value, value, .... Values
• A value may be an object, an array, a litteral
  (string, number, true, false, null).
• Nothing more is required to create a JSON file!

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Example

•    "menu" "File",    "commands"       
             "title" "New",           
  "action""CreateDoc"       ,       
             "title" "Open",           
  "action" "OpenDoc"       ,       
             "title" "Close",          
  "action" "CloseDoc"            

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XML Equivalent

• lt?xml version"1.0" ?gt ltrootgt  
  ltmenugtFilelt/menugt   ltcommandsgt     
  ltitemgt          lttitlegtNewlt/valuegt         
  ltactiongtCreateDoclt/actiongt      lt/itemgt     
  ltitemgt          lttitlegtOpenlt/valuegt         
  ltactiongtOpenDoclt/actiongt      lt/itemgt     
  ltitemgt          lttitlegtCloselt/valuegt         
  ltactiongtCloseDoclt/actiongt      lt/itemgt  
  lt/commandsgt lt/rootgt

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How to use the format

• The JSON file allows to load data from the server
  or to send data to it, in this format. For
  example, storing the content of a form, just
  filled by an user. This involves three steps the
  browser processing, the server processing, and
  the data exchange between them.
• Client side (browser)
• This is rather easy, as JSON is a part of the
  JavaScript definition. The content of a file, or
  the definition of the data is assigned to a
  variable, and this variable becomes an object of
  the program.
• Server side
• JSON file are used by various programming
  languages, including PHP and Java thanks to
  parsers that allow to get the content and that
  may even convert it into classes and attributes
  of the language.The json.org includes a C parser
  and a list of parsers in other languages.
• Data exchange
• Loading a file may be accomplished from
  JavaScript in several ways- direct including of
  the file into the HTML page, as a JavaScript .js
  external file.- loading by a JavaScript
  command.- using XMLHttpRequest.The JSON file is
  parsed by the eval() JavaScript
  function.Sending the file to the server may be
  accomplished by XMLHttpRequest. The file is sent
  as a text file and processed by the parser of the
  programming language that uses it.

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Example

• The XMLHttpRequest code
• var req new XMLHttpRequest()
• req.open("GET", "file.json", true)
• req.onreadystatechange myCode // the handler
• req.send(null)
• The JavaScript handler
• function myCode()
• if (req.readyState 4)
• var doc eval('(' req.responseText ')')
• Using the data
• var menuName document.getElementById('jsmenu')
  // finding a field menu
• Name.value doc.menu.value // assigning a value
  to the field
• How to access data
• doc.commands0.title // read value of the
  "title" field in the array
• doc.commands0.action // read value of the
  "action" field in the array