Web Services. What are Web Services? r Today, we normally use Web browsers to talk to Web sites m Browser names document via URL (lots of fun and games.

Web Services

What are Web Services?

Today, we normally use Web browsers to talk to Web sites Browser names document via URL (lots of

fun and games can happen here) Request and reply encoded in HTML, using

HTTP to issue request to the site Web Services generalize this model so

that computers can talk to computers using much of the same protocols used to communicate between browsers and web servers + a lot more.

What are Web Services?

The concept of Web Service (WS) was introduced in 1999 by Hewlett-Packard. Microsoft coined the actual term “Web Services” in June 2000 as part of the .NET initiative.

Web services are often advertised as a new wave in business process automation Is suppose to allow a seamless integration of systems and

applications that communicate over the network and share data. This technology is in its infancy.

Work in progress Unproven Lots of hype?

What are Web Services?

Idea of treating software as a service. Nothing new

Evolution of many different technologies Remote Procedure Calls (RPC) CORBA DCOM Java RMI

What is novel? Overwhelming industry support Utilization of XML

Why Web Services

SUN RPC, DEC, CORBA, DCOM, Java RMI Not considered Internet-friendly Interoperability issues: standards are not always clear. Cannot be implemented in any language on any

platform Software components that comprise the application

are often not useful except for that application A web service

Can be implemented in any language on any platform Black boxes

• Component-like, reusable Based on Web standards

• HTTP, XML, SOAP, WSDL, UDDI

Examples of Simple Web Services

Return the distance in miles between 2 locations

Locate entertainment, restaurants and lodging in a given area

Return the name and the postal address associated with a given phone number.

Find ATM location for a given postal code.

Return stock quotes.

Examples of Web Services

A travel agent needs to book a flight, hotel and car in a warm place. The client wants the best prices. Travel agent contacts each airline for flight information, hotel chain for hotel information and car rental agencies. The airlines, hotel chains and car rental

agencies can be thought of as web services from the travel agent’s perspective.

The travel agent’s user may think of the travel agent as a web service.

Examples of Web Services

You should note the potential reusability of each of the services described on the last two slides.

Web services provide interoperability between various software applications running on various platforms.

Web services leverage open standards and protocols.

Web Services Architecture

(1) Publish

Service Directory

ServiceProvider

ServiceRequestor

(2) Discover Services

(3) Invoke Services

Web Services Architecture

Service Provider Implements the Web Service and makes it

available on the Internet Service Requestor

Consumer of the Web Service Service Directory

Logically centralized directory of services Place to publish a new web service or find

existing one.

XML

XML – Extensible Markup Language Open standard for data exchange; for

describing data which allows an infinite range of elements (tags) to be defined: Tags define content Separation of content from presentation

SOAP SOAP – Simple Object Access Protocol

Created by Microsoft and submitted to W3C in 1999 Multivendor support including IBM, Sun, Oracle, HP,

etc; SOAP operates as RPC mechanism with HTTP

used as transport protocol. Encodes requests and responses as XML

documents. SOAP is suppose to be simple, easy to extend

and interoperable.

SOAP Elements Envelope (mandatory)

Top element of the XML document representing the message

Header (optional) Determines how a recipient of a SOAP message should

process the message Adds features to the SOAP message such as

authentication, transaction management, payment, message routes, logging, auditing, etc…

Body (mandatory) Exchanges information intended for the recipient of

the message. Typical use is for RPC calls and error reporting.

Soap RequestSOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"

SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>

<SOAP-ENV:Body> <m:GetLastTradePriceRequest xmlns:m="Some-URI"> <symbol>HP</symbol> </m:GetLastTradePriceRequest> </SOAP-ENV:Body>

</SOAP-ENV:Envelope>

Identifies XML has SOAP message

Soap RequestSOAP-ENV:Envelope

xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"

SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>

<SOAP-ENV:Body> <m:GetLastTradePriceRequest xmlns:m="Some-URI"> <symbol>HP</symbol> </m:GetLastTradePriceRequest> </SOAP-ENV:Body>

</SOAP-ENV:Envelope>

Get price for HP stock

SOAP Response

<SOAP-ENV:Envelope

xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"

SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>

<SOAP-ENV:Body> <m:GetLastTradePriceResponse xmlns:m="Some-

URI"> <Price>34.5</Price> </m:GetLastTradePriceResponse> </SOAP-ENV:Body> </SOAP-ENV:Envelope>

WSDL

WSDL – Web Services Description Language

Type of XML used to describe abilities of Web Service to its potential user.

WSLD provides the standard method of describing web services and their specific capabilities to other applications.

Elements in WSDL Definitions Types

Based on XML Schema type system Message formats

Parts represent method parameters Port Types

Set of operations Parameter order Input and output messages

Bindings Map a Port Type to a specific protocol, using a specific data

encoding style Services

Set of ports that implement port types Access point for each port

<definitions>

<types> <!-- XML Schema --> </types>

<message name=“getQuoteRequest” />

<message name=“getQuoteResponse” />

<portType name=“StockQuoteServiceInterface”>

<operation name=“getQuote”>

<input message=“getQuoteRequest” />

<output message=“getQuoteResponse” />

</operation>

</portType>

<binding name=“StockQuoteServiceBinding” type=“StockQuoteServiceInterface”>

<soap:binding transport=“http://schemas.xmlsoap.org/soap/http” />

…

</binding>

<service name=“StockQuoteService”>

<port name=“StockQuoteServicePort” binding=“StockQuoteServiceBinding”>

<soap:address location=“http://www.acme.com/services/stockquote” />

</port>

</service>

</definitions>

WSDL – An Example

Definition of data types

Definition of messages

Definition of port type

Definition of the bindings

Definition of the service

UDDI

UDDI – Universal Description, Discovery, and Integration Enables the creation of searchable web service

directory that allows for the registration of a service and in response to a user provide the location of a service.

Search by business or service type Has a Web Services API for publishing and discovering

the existence of Web services A coalition of organizations working together to manage

UDDI registries and to further develop the Web Services API for accessing those registries.

How UDDI Works

UDDI Business Registry

3. Assigns a unique identifier to each business registration

Marketplaces, search engines, and business apps query the registry to discover services at other companies

4.SW companies, standards bodies, and programmers populate the registry withdescriptions of different types of services

1.

BusinessRegistrations

2.

Businesses populate the registry withdescriptions of the services they support

Business uses this data to facilitate easier integration with each other over the Web

5.

Web Service Example(from SUN)

Suppose that the owner of a chain of coffee houses, called Coffee Break, wants to expand by selling coffee online.

The owner instructs the business manger to find some new coffee supplier, get their wholesale prices, and then arrange for orders to be placed as the need arises.

Coffee Break can analyze prices and decide which new coffees it wants to carry and which companies it wants to buy them from.

Web Services Example (from SUN)

Locate coffee supplier through a UDDI service directory.

The Coffee Break will issue a query to the UDDI service directory. When the search is completed, the registry will send back information on how to contact the wholesale coffee distributors that meet the criteria set out in the query.

Web Services Example

Now Coffee Break can request price lists from each of the coffee distributors returned by the UDDI Service Directory. The Coffee Break has obtained a WSDL

description for each distributor which describes the procedure to call to get prices and the URL where the request is to be sent.

Upon receiving the responses for the request for prices, Coffee Break processes the price lists. This is used to send orders.

Traditional RPC vs Web Services

Traditional RPC Within enterprise Tied to a set of

programming languages

Procedural Usually bound to a

particular transport Tightly-coupled Firewall-unfriendly Efficient processing

Web Services Between enterprises Program language

independent Message-driven Easily bound to

different transports Loosely-coupled Firewall-friendly Relatively not

efficient processing

Challenges Standards are new and require further

development as to make sure that there is true interoperability.

Lack of Security Controversy over royalty fees (intellectual

property rights to SOAP, WSDL, UDDI are held by Microsoft and IBM).

Management, monitoring, auditing Performance: WS may be too slow for high

performance applications since parsing XML takes time.

Quality of Service: Lack of standards describing quality of various web services.