IS705 Class 1: Introduction to Web Services

Transcript IS705 Class 1: Introduction to Web Services

Aug 4, 2003

Tutorial

Introduction to Web Services By Mark Gaynor Boston University School of Management

Agenda

    What is a web service?

  Nobody really agrees!

“Using XML and SOAP to access distributed computing resources” – a good starting point Why are they good – interoperability is valuable Web services architecture  Expose business logic to other applications Business implications  Is this what we have been waiting for?

 How about EDI, we were waiting for this also Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

What is a web service? (1)

  Loosely coupled, reusable software components that semantically encapsulate discrete functionality and are distributed and programmatically accessible over standard Internet protocols”

(Sleeper 2001)

. Not so good – web services can have different degrees of coupling Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Tight vs. Loose Coupling

Tight coupling  Very efficient interaction   Very compressed communication Requires “deep knowledge” Loose coupling  Less efficient interaction   Not as many subtle details conveyed Does not require “deep knowledge” Aug 4, 2003 Bala, course,F02 BU Student Hay Bala, what course are you teaching?

Bala Now I am teaching a course about using information …..

Prof.

IS323 Bala AMCIS 2003

What is a web service? (2)

  First take: a replacement for “form scraping” Second take: Software component (module)  Platform independent – Maybe (ask Microsoft)     Language independent – Maybe (ask Sun) Implementation independent Available over a network   Can be easily discovered and learned about Can be easily invoked May be composed with other services Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

What is a web service

  A component with distributed access based on Internet standards A definable piece of business logic for internal or external use SOAP message

XML:

Temp for: Cambridge MA Weather-service SOAP message

XML:

Temp is: 91.5F

Client Aug 4, 2003 © Mark Gaynor, et al. 2003 Web services Yellow Pages Weather-service Directions for use Time-service Traffic-service AMCIS 2003

Example

Online shopping application Credit card verification & Authentication of user: Client Aug 4, 2003 WAN

SOAP

Credit card verification & Authentication of users web service Credit card verification: Client

SOAP

WAN Credit card verification web service Authentication of user: Client

SOAP

Authentication of users web service Web Server © Mark Gaynor, et al. 2003 Web

(soap)

Services Server AMCIS 2003

Why Web Services?

  Standardized distributed computing environments create value  The more users, the greater the value Dynamic Business Networks require Dynamic Information Systems   From a technical point of view web services allow this Common acceptance of a single standard allows the politics to work Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Owner Business model

Stakeholder Views of Web Services

Architect Component requirements Builder design principles,component requirements) End-user Requests Web Service Capabilities Web Service Architectures Web Service Products Web Service Applications Feasibility/ Business component requirements Design principles, Component requirements & interfaces Source: (Iyer et al 2003) Application Build-out & integration Results

Service-Oriented Architecture

Service Registry Find Publish Aug 4, 2003 Service Requestor Bind (HTTP) © Mark Gaynor, et al. 2003 Service Provider AMCIS 2003

Web Services Architecture

Service Registry Find Publish Aug 4, 2003 Service Requestor SOAP / XML Bind (to protocol) © Mark Gaynor, et al. 2003 Service Provider AMCIS 2003

Points to consider

    Are web services really tied to the web?

 Some are, some are not First time everybody has agreed to a common standard How are web services different from remote procedure calls?

How are web services different from EDI  They expose business logic to your partners Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Remote Procedure Call (RPC)

  What  Client calls procedure contained in server How   Stub procedure in client marshals parameters into a message Message sent to server  Skeleton procedure on server    converts message back to parameters calls procedure sends return message Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Other RPCs – A history

    DCE – Distributed computing environment DCOM – MS distributed component object model CORBA – Common object request broker architecture: language and platform independence Java RMI – Remote method invocation  Java VM gives platform independence Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Web Services are Much More

    They are very flexible, hence not well defined They may be applications communicating with messages They may be a fancy RPC architecture They may be something we have not discovered yet Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Grid and Web Services

   Does anybody know what the grid is?

A distributed computing enviroment.

 Sounds like a web service!

A grid service might be a bandwidth intensive super computer type problem  Or may not. Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

What’s Wrong With the Picture?

   Vendors, and pundits agree, but remember they are never right!

 Remember OSI, X.400 email, and ATM The overhead may be very high (100X)  There are some research ideas to help this Too much hype Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Key technologies

    XML  describe the information to be exchanged SOAP  package the information and move it between client and service WSDL  Describe a service UDDI  Provide a list of available services Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

XML – Describes Complex Data

   XML can describe documents & data  Document v. Data -- What is the difference?

 For web services our primary interest is in data XML is used to describe both data structure, and data  Data structure: what each bit is supposed to mean XML describes complex, hierarchical data structures  In a form that is easily processed by a computer Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

SOAP – Simple Object Access Protocol

     Very flexible message architecture SOAP is defined using XML SOAP provides an envelope Two styles of SOAP messages   RPC – remote calling XML data message – send/receive arbitrary XML data SOAP can be used over HTTP, SMTP, FTP Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

SOAP RPC

    Encode the RPC call into a SOAP envelope with XML data RPCs rely on special-purpose APIs RPCs are vulnerable to small changes in API or data structure  Limited “separation of concerns” between client and service Tightly coupled!

Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

SOAP RPC Trade-offs

 Advantages  Well understood   Automatically encodes/decodes application data Easy to synchronize  Disadvantages  Not very flexible   Server must be running for call to succeed Only one-to-one interaction Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

SOAP Messaging

   Send XML data from one application to another – loose coupling!

More flexible than RPC Queued Vs Direct Sender Aug 4, 2003

Direct

Recipient Sender © Mark Gaynor, et al. 2003 Queue

Queued

Recipient AMCIS 2003

SOAP Messaging Trade-offs

 Advantages  Simple API    Any data can be passed Separates data from code Allows disconnected operation (if queued)  Disadvantages  Application must encode and decode data  Queued systems are asynchronous, which may be hard to program Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

WSDL – Describing Web-Services

   How does the client know how to access the web-service?

What are the parameters, and their data types?

What is returned by the service?

Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

UDDI – Register Web-Services

     Helps find the service Just a list of services Will this be by people, or programs?

Useful to look at many different services to decide which one you want You, too, can browse UDDI registries Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Overview

    XML SOAP WSDL UDDI Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

HTML Review

 HyperText Markup Language   Mark up text with “tags” to identify formatting and links Here is some

text

a tag in the middle.

Here are the tags you can use with Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Examples

    Emphasize some text  4 days of classes to go!

A heading 

Ozzie’s Weblog

A hypertext link  BU A list

milk

Aug 4, 2003

soup

HTML Limitations

    Inflexible Focus on formatting not content No semantics Presentation not data Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Enter XML

 XML (eXtensible Markup Language) is programming language!

not a  XML is a standard (a set of rules, guidelines or conventions) for designing data format for structured document interchange on the Web.  XML is defined by The World Wide Web Consortium (W3C). Source: (W3C 2001) http://www.w3.org/XML/1999/XML-in-10-points Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Why XML? HTML Limitations

    Inflexible Focus on formatting not content No semantics Presentation not data Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

XML is for Structuring Data

 Structured data examples:  Spreadsheets    Address books Financial transactions Technical drawings  XML makes it easy for a computer to:  Read data  Generate data  Ensure that the data structure is unambiguous Source: (W3C 2001) http://www.w3.org/XML/1999/XML-in-10-points Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

XML Looks a Bit Like HTML

  Use of   tags (words bracketed by '<' and '>') and attributes (of the form name="value") Tags:   Only delimit pieces of data Leave the interpretation of the data completely to the application that reads it Source: (W3C 2001) http://www.w3.org/XML/1999/XML-in-10-points Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

XML is New, but Not that New

 Development of XML started in 1996  Has been a W3C Recommendation since February 1998.

Source: (W3C 2001) http://www.w3.org/XML/1999/XML-in-10-points Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

XML Applications v. Processors

 XML

Application

 A markup language derived using XML  XML

Processor

 Software created to process XML documents Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

“Hello World” XML Example

Hello, world! Stop the planet, I want to get off! Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Example Application #1: XHTML

 XHTML is the successor to HTML  An application restricts XML syntax  XHTML allows "

", but not ""  An application adds semantics to XML syntax  XHTML says that "

" stands for "paragraph", not for "price" Source: (W3C 2001) http://www.w3.org/XML/1999/XML-in-10-points Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

But there’s more!

XML is Modular

  XML allows you to define a new document format by combining and reusing other formats.

To eliminate name confusion when combining formats, XML provides a namespace mechanism.

Source: (W3C 2001) http://www.w3.org/XML/1999/XML-in-10-points Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

XML Namespace

 Tags can be given a prefix to identify context  Example: does solution refer to chemical compound or mathematical answer?

  Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

What is SOAP?

  Simple Object Access Protocol XML-based protocol for exchange of information in a distributed environment.

   Route information to remote process Deliver binary data using MIME attachments Encapsulate RPC calls Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

SOAP Message

  A

header envelope

and a

body

   contained in an Header: directives for the SOAP processor Body: data to be delivered to remote recipient Envelope: contains header & body Envelope must be prefaced by protocol binding Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Simplified Example



 For simplicity have omitted namespace, XML directives, and other niceties Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Protocol Binding

   SOAP message is delivered by underlying protocol (typically HTTP) Protocol binding consists of directives to underlying protocol as to how to deal with SOAP message For HTTP includes  SOAPAction (optional)    Host = … Content-Type = text/xml; charset=… Content-Length = … Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Special Messages

 SOAP-RPC  Represents remote procedure call & response  SOAP-Fault  Reports errors encountered in SOAP processing Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

SOAP-RPC

  The procedure call is encoded in the SOAP body The call takes the form value  Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

SOAP-RPC (2)

   The response uses similar format Datatype of parameters is defined via a SOAP-Encoding Attribute  Example: Other aspects of RPC defined via WSDL Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Challenge: Can you identify the SOAP elements here?

POST /StockQuote HTTP/1.1 Host: www.stockquoteserver.com Content-Type: text/xml Content-Length: nnnn SOAPAction: Some-Namespace-URI#GetLastTradePrice

Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/ DIS

Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

This is the Response to the Previous Message HTTP/1.1 200 OK Content-Type: text/xml; charset="utf-8“ Content-Length: nnnn

Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/ 34.5

Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

What is WSDL?

   Web Services Description Language   XML format Defined by W3C Describes the internal structure of a web service Extensible  No commitment to specific message formats or network protocols Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Elements of WSDL

  Message  Used to communicate with the web service portType   A group of operations offered by one endpoint of the web service There can be more than one portType (endpoint) for a single web service Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Elements of WSDL (2)

  Binding  Maps a portType to a concrete protocol and data format (e.g. SOAP) Service  Maps each binding to a port located at some endpoint on the network Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Message

 Gives the data structure of each message (e.g. the parameters used in an RPC call) Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

portType



  The sequence of messages defines the behavior of the operation msgID points to one of the messages defined above Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Operation

 A set of messages which accomplishes some function Operation Behavior Sequence of Messages Request-response Input then Output Solicit-response Output then Input Notification One-way Output only Input only Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Binding

   Protocol specific binding extensions  HTTP, SOAP, and MIME are standard Each portType is associated with a binding Example: SOAP  Specifies type (document or RPC)  Specifies how messages are placed in the header and body Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Service

Brief description of the service



Source: (Christensen et al 2001) http://www.w3.org/TR/2001/NOTE-wsdl-20010315

Service (2)

  Used to aggregate a set of related ports Relationship between ports within a service:  None of the ports communicate with each other.   If a service has several ports that share a port type, but employ different bindings or addresses, the ports are alternatives.

 Allows a WSDL document consumer to choose particular port(s) to communicate with based on some criteria (e.g., distance). By examining its ports, we can determine a service's port types.  Allows a WSDL document consumer to determine if it wishes to communicate to a particular service based whether or not it supports several port types.

WSDL Design Issues

   Decomposition of a service into ports Granularity of operations Structure of the service, messages, data elements, and so on Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

What is UDDI?

  Universal Description, Discovery and Integration  An industry initiative to enable businesses to quickly, easily, and dynamically find and transact with one another. (www.uddi.org)  A specification under the ausipices of OASIS UDDI enables a business to  Describe its business and its services  Discover other businesses that offer desired services  Integrate with these other businesses.

Source: (OASIS 2003) http://www.uddi.org/faqs.html

The UDDI Business Registry (1)

   Provides a place for a company to register its business and the services that it offers.

People or businesses that need a service can use this registry to find a business that provides the service.

Operated as a distributed service.

 Currently, IBM and Microsoft operate registry nodes.  Access to and from the UDDI Business Registry is performed using SOAP.

 However, a service registered in the UDDI Business Registry can expose any type of service interface.

Source: (OASIS 2003) http://www.uddi.org/faqs.html

The UDDI Business Registry (2)

 Records the following information:     Business Entity  A business entity represents information about a business (name, contact information, description, and a URL pointing to more information about the business). Business Service  Associated with the business entity is a list of business services offered by the business entity. Specification Pointers  Associated with each business service entry is a list of binding templates that point to specifications and other technical information about the service. Service Types Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Source: (OASIS 2003) http://www.uddi.org/faqs.html

What is UDDI NOT?

  The UDDI Business Registry:  Not a general-purpose search engine    A search engine uses free-text queries to search unstructured data.

The UDDI Business Registry has very structured data.

 A query against the UDDI registry can only retrieve data stored within the registry.

Traditional search engines could use the UDDI Business Registry as a source when compiling their responses and results.

UDDI project is not "run" by any one company.

 Currently guided by industry leaders spearheading the early creation and design efforts Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

.NET and J2EE

Building Web Services

Web Service Development Environment

  Microsoft believes that you should be able to use any language to write a web service – They are right!

 As long as you use a Microsoft Platform Sun believes that you should be able to use any platform you want – They are right!

What is Microsoft® .NET?

•Microsoft software technologies •Connecting information, people, systems, and devices •Helps developers

create XML Web services

and

stitch them together

•Benefit to individuals: •Seamless, compelling experiences with information sharing •.NET connected software •Uses a distributed computing model •Builds on open standards like XML to connect PCs and other smart devices Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

.NET basics

.NET Framework

•The .NET framework has two components: •The common language runtime •Agent that manages code at execution time, providing core services such as memory management, thread management, remoting, etc… •.NET framework class library •Object-oriented collection of reusable types that can be used to develop applications ranging from traditional command-line or graphical user interface (GUI) applications to applications based on the latest innovations provided by ASP.NET

, such as Web Forms and XML Web services.

What is ASP.NET?

•

Hosting environment

that enables developers to use the .NET Framework to target Web-based applications.

•Architecture for developing Web sites and Internet distributed objects using managed code.

•XML Web services use ASP.NET as the publishing mechanism for applications.

What is J2EE?

•Java 2 Platform, Enterprise Edition •Component-based approach to the design, development, assembly, and deployment of enterprise applications •Not tied to the products or APIs of any one vendor •Freedom to choose products/components that best meet • needs •J2EE Offers:

Multitiered distributed application model

•Ability to reuse components •XML-based data interchange •Unified security model •Flexible transaction control Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Distributed Multitiered Applications

•Application logic is divided into

components

according to function and the various application components that make up a J2EE application are installed on

different machines

depending on the tier in the multitiered J2EE environment to which the application component belongs. •The J2EE specification defines the following

components

:  Application clients and applets : run on the client.  Java Servlet and JavaServer Pages (JSP) technology  Web components that run on the server  Enterprise JavaBeans (EJB) components (enterprise beans)  business components that run on the server Aug 4, 2003 © Mark Gaynor, et al. 2003 AMCIS 2003

Multitiered Applications

Web services implications

    Enterprise integration Cross-enterprise business processes Nice way to access legacy applications with Internet technology Is web-services the answer, no matter what the question?

References

 These slides are based on a lecture given by two of the authors as part of a new course, Issues in Managing Networked Systems, taught at the BU School of Management.

 Material drawn from online sources is cited with URL on individual slides.

 Additional references  Sleeper, B. "Defining Web Services," San Francisco: The Stencil Group, 2001.

 Iyer, B., Freedman, J., Gaynor, M., and Wyner, G. "Web Services: Enabling Dynamic Business Networks,"

Communications of the AIS

(11), 2003.