Chapter 6 Introduction to Web Services

Objectives By study of the chapter, you will be able to: Describe what is Web services Describe what are differences between website access and Web services Describe what Web services can do and cannot do Identify the key components or technologies involved in Web services Identify who manages the Web services specifications examine the examples of the Web services Questions and Discussion Homework

What is Web services? A Web service is a software application that can be accessed remotely using different XML-based languages A Web service normally identified by a URL, just like you access any other website. You can use the service provided by the website, such as currency exchange rate and calculation, weather reports for a specified city, or language translation Those services are not stored at your computer, but in the server. You will can those services remotely at your computer to the remote server via the Internet

What is Web services? (continue) Your request for a Web service will be transmitted by XML and send the request with all parameters to the Web services server Then the request will be received, parsed, and executed by the server. Finally, the result of the service as a response, will be sent back to your screen, and extracted by SOAP message parser Doesn’t matter what operating system and computer language you use, A Web service will recognize your request, since it follows all of the standards, especially the XML and SOAP appliances Example of a Web service Example of a Web service –World Lingo (a free online translator) World LingoWorld Lingo

What are the difference between website access and Web services Most websites are designed to provide a response to a request from a user; furthermore, the user either type in the URL, or click on a hyperlink, to create a request. This request then takes the form of a text document that contains some fairly simple instructions for the server In a website access, these instructions are limited to the name of a document to be returned or a call to a server-side program with a few parameters

What are the difference between website access and Web services (continue) However, in a Web service, the content in a request from a user to the server is sending by XML document The document formatted in a special way in accordance with the rules of the SOAP specification A SOAP message can contain a call to a method along with any parameters that might be needed The complexity of a SAOP message far exceeds the complexity that is possible using only a Web browser We will discuss SOAP in later chapters

What are the difference between website access and Web services (continue) In summary, a Web service uses XML specification, but a website uses a text document A Web service follows SOAP specification, but a website only follows a web browser’s rules, so that its complexity to handle the request is greatly limited

What Web services can do and cannot do It doesn’t matter what kind of computer sends the SOAP message or on what operating system it’s running It’s doesn’t matter where in the world the client or user is sending the request for a service from It doesn’t matter what language the software that the client is running on was written in There is no need for the client to know what type of SOAP processor is running on the server

What Web services can do and cannot do Web services have the great promise that every software application in the world can potentially talk to every other software application in the world, doesn’t matter the boundaries of location, hardware, operating system, language, protocol and so on However, this Holy Grail computing is just begun; there is much work to be done before this promise is realized Areas such as security, transaction support, and business process execution are being addressed, but not yet incorporated into the SOAP specification

Identify the key technologies involved in Web services SOAP –Stands for Small Object Access protocol –Is a specification that defines an XML grammar for both sending messages and responding to messages that you receive from other parties –The goal of SOAP is to describe a message format that is not bound to any hardware or software architecture –SOAP can be downloaded from open source software foundations such as Apache; or you can purchase it from a vendor such as Microsoft, IBM, and so on; or you may write your own SOAP components –SOAP contains two parts: the header that carries processing instructions and the body that contains the message that you want to send

Identify the key technologies involved in Web services (continue) –There are two types of SOAP message: document and RPCs (Remote Procedure Calls) –Document is any XML document you want moved from one computer to another –An RPC is a method call that is intended to be executed on the Web service’s computer –An RPC performs the same function as an ordinary method call; the difference is that this call can take place over the Internet on a server machine –Example of a SOAP program (next slide)

Identify the key technologies involved in Web services (continue) <SOAP-ENV:Header> admin admin rover> rover> </SOAP-ENV:Header><SOAP-ENV:Body><checkAccountBalance> </checkAccountBalance></SOAP-ENV:Body>

Identify the key technologies involved in Web services (continue) XML (eXtensible Markup Language) –Is the language that all the Web services programs built on –Is a tool for constructing self-describing documents –Is used to create your own grammars –An XML schema can describe these grammars that specify the tags that are allowed and the relationships between the elements defined by these tags

Identify the key technologies involved in Web services (continue) –SOAP and all other Web service technologies are all XML-based grammars –Example of an XML program <ticketRequest> <lastName>Wang</lastName><firstName>Gong</firstName></customer>

Identify the key technologies involved in Web services (continue) HTTP (Hypertext transport Protocol) –Is a standard that precedes the advent of Web services –Was developed to facilitate the transfer of requests from a browser to a Web server – Web services take advantage of the existence of this mature protocol to move SOAP message and WSDL documents from one computer to another

Identify the key technologies involved in Web services (continue) WSDL (Web Services Description Language) –Is a specification that tells us how to describe the method calls that it responds to –These method calls are described in an abstract way that is independent of what programming language the actual service is written or what operating system it runs on –It also contains a concrete section in which the various details of how to actually make a connection to the service are stored; for example, a Web service may be accessed using HTTP, FTP, or SMTP, you will define three sections and one for each service

Identify the key technologies involved in Web services (continue) –Example of a WSDL program (service element) <wsdl:documentation> This tag is for adding new service </wsdl:documentation> </wsdl:port></wdsl:service>

Identify the key technologies involved in Web services (continue) UDDI (Universal Discovery Description Integration) –Is a specification that describes how a potential customer of a Web service could learn about its capabilities and obtain the basic information needed to make the initial contact with the site –Is also registries to specify if a Web service is a public, private, or semiprivate –A public Web service registry allows everyone to access

Identify the key technologies involved in Web services (continue) –A private registry exists behind the firewall of your organization and is only accessible by authorized members –A semiprivate registry is open to a limited number of outsiders such as your best trading partners –We will discuss UDDI in later chapter

Identify who manages the Web services specifications Specifications are about standards, rules, conventions, and suggestions in the field, particularly here, in Web services industries W3CW3C (World Wide Web Consortium) W3C –The most important organization in Web services –W3C is a forum for information, commerce, communication, and collective understanding –W3C manages SOAP, WSDL, XML, XML Schema, and HTTP specifications –W3C also manages Web services architecture document, which is currently in a draft status

Identify who manages the Web services specifications (continue) OASISOASIS (Organization for Advancement of Structured Information Standards) OASIS –Is a not-for-profit, global consortium that drives the development, convergence, and adoption of e-business standards –It manages UDDI, WS-Security, and SAML (Security Assertion Markup language) specifications and others

Identify who manages the Web services specifications (continue) WS-I WS-I (Web Services Interoperability) WS-I –Is a new established and open industry organization that promotes Web services across all platforms, operating systems, and programming languages –Works across the industry and standards organizations to customer needs by providing guidance, best practices, and the resources for developing Web services solutions

Examine the examples of the Web services Popular Web services websites: – –Check US Holidays using Web service: ayDates.asmx ayDates.asmx – –Free US government justice Web services

Questions and Discussion

Homework for Extra Points Using examples to explain what are differences between a website and a Web service? Why Web services, rather than using websites? Do a search to find a free Web service you are interested in and execute it. Copy and paste the execution result to a Word file, and save it as “webservicetryit.doc” Due: Wednesday, May 11, 2005 in the class