Chapter 9 Web Services Architecture and XML

Objectives By study in the chapter, you will be able to: Describe what is the goal of the Web services architecture Conduct the historical review of other technologies before Web services Describe why the previous technologies are dissatisfied by the industries Exam what Web services can provide to allow us to avoid those problems Exam the major components of the architecture Describe how to make interactions between components in a Web service

Objectives Describe the components and structure of XML Exam the similarity and differences between XML and HTML Analyze the namespace and schema of XML Be able to write XML documents Questions and Discussion Homework

The goal of the Web services architecture Is application-to-application communication over the Internet. More specifically, this communication is performed with the idea of facilitating Enterprise Application Integration (EAI) and e-commerce, specially business-to-business e- commerce

Historical review of other technologies before Web services Web service is not the first attempt to reach the goal described before There are two major technologies even still available today to that attempt. They are: –CORBA (Common Object Request Broker Architecture) –DCOM (Distributed Component Object Model)

Historical review of other technologies before Web services (continue) What is CORBA? –Is released in 1991 by OMG (Object Management Group, Inc.) –Is language neutral and designed to work any language –Is using Stub/Skeleton based architecture –Is supported by many third-party vendors –More information about CORBA:

Historical review of other technologies before Web services (continue) What is DCOM? –Is released in earlier 1990’s by Microsoft to compete with OMG’s CORBA –Is using stub/skeleton based architecture –It can be built with Visual C++, Visual Basic, C#, and other languages –It only works with Microsoft Windows platforms –More information about DCOM: en-us/dndcom/html/msdn_dcomarch.asp en-us/dndcom/html/msdn_dcomarch.asp

Why the previous technologies are dissatisfied by the industries They are not to support asynchronous remote method calls They are weak in data encoding with binary formats only Programmer-defined data is not easy to work with CORBA and DCOM Data validation has to tie with program logic without the separation They are competing but rarely interoperating

What Web services can promise? Provides an approach that allow us to avoid many of the problems that CORBA and DCOM suffer from Supports message-centric asynchronous transactions as well as RPC-style synchronous transactions with equal ease Emphasizes on application integration and interoperation-ability Utilizes XML schema for data encoding

What Web services can promise? (continue) Utilizes XML documents that are human and machine readable and make debugging easier Utilizes XML to support arbitrary or programmer-defined data by using the WSDL in its description Separate Data validation from the program logic by adding to any XML document in ease

Major components of the architecture The following software specifications are considered as components of Web services: –HTTP –HTTP State Management mechanism (cookies) –SOAP –UDDI –WSDL –XML

Major components of the architecture (continue) HTTP –HyperText Transport Protocol –Current version 1.1 is required in Web services –Purpose of HTTP is to provide communications protocol to move the requests and responses between clients and servers –It’s a popular way to transport SOAP messages between clients and Web services –HTTP may be optional if SOAP 1.2 is used as a component in Web services because other protocols have been added

Major components of the architecture (continue) HTTP State Management Mechanism (Cookies) –It’s also called as RFC 2965 –It specifies how to create stateful sessions using HTTP requests and responses –It carries three headers’ information between participating clients and services ( ) –More information about RFC

Major components of the architecture (continue) SOAP (Simple Object Access protocol) –See explanation of the terminology and example in slides of Chapter 6 –We will discuss WSDL in next chapter

Major components of the architecture (continue) WSDL (Web Services Description Language) WSDL (Web Services Description Language) –See explanation of the terminology and example in slides of Chapter 6 –We will discuss WSDL in next chapter

Major components of the architecture (continue) UDDI (Universal Description, Discovery, and Integration) –See explanation of the terminology in slides of Chapter 6 –We will discuss UDDI in next chapter

Major components of the architecture (continue) XML (eXtensive Markup Language) –We will discuss it next

Interactions between components

Introduction to XML The components of XML –XML document A file that obeys the rule of XML –XML parser A software that takes XML as its input and produces a readable representation of its contents –Document Type definition (DTD) A description of the tags that are allowed in a document and their relationships to each other The DTD was made obsolete by the publication of the XML schema specification in 2001

Introduction to XML (continue) –XML schema A description of the tags that are allowed in a document and their relationships to each other –Namespaces A unique name can be used to avoid conflicts between tags names because a document may contain other XML documents so we must guarantee none tag names are identical to others

Simple Example of XML <SHOWS><PERFORMANCE> Fairy Princess Fairy Princess <AUTHOR/><DESCRIPTION> Scratch sound with emphasis on color, texture. </DESCRIPTION> 04/16/ /16/2002 </PERFORMANCE></SHOWS> is an empty tag without data --> is an empty tag without data -->

Simple Example of XML (continue) Execution result in Netscape 6.0: Fairy Princess Scratch sound with emphasis on color, texture. 04/16/2002 Execution result in Internet Explorer: - - Fairy Princess Fairy Princess Scratch sound with emphasis on color, texture. Scratch sound with emphasis on color, texture. 04/16/ /16/2002 </SHOWS>

XML vs. HTML in syntax Every XML document must have one root element, i.e., ….. Every XML document must have one root element, i.e., ….. Tags are case-sensitive in XML, but not in HTML No whitespace is permitted at the beginning of a tag (i.e., is not allowed), however whitespace at the end of tag is allowed (i.e., is okay), but not a case in HTML

XML vs. HTML in syntax (continue) The tag name must start with either a letter or an underscore, but user-defined tags are not allowed in HTML The tag names may contain any of following: letters, numerals, hyphens, periods, or underscores The tag names may contain any of following: letters, numerals, hyphens, periods, or underscores

XML vs. HTML in syntax (continue) Each tag must have an end tag, the same as HTML: i.e, ……………., or just an empty tag as, which is incorrect in HTML Tags must be nested i.e., ….. ….. is incorrect, but is okay in HTML Attribute values must be enclosed in quotes i.e., date status=canceled is incorrect Comments use the same HTML syntax i.e., i.e.,

XML Structure Each XML file starts with an optional prolog:, or, or Each XML file must have one and only one root element Each XML file may have DTD section or schemas section

Another example of XML file <ticketRequest> <customer custID=“1003” <lastName>Carter</lastName><firstName>Joseph</firstName></customer> <destination>Hawaii</destination><port>Honolulu</port><sailing>7/7/2005</sailing><numberOfTickets>5</numberOfTickets></isCommissionable></cruise></ticketRequest>

Namespaces in XML To be able to have unique tag names in an XML file, as namespaces, a prefix string is added before each tag and defined at the beginning of the root tag using a unique URL; for example:

XML schema and example Since the DTD did not allow us to specify data types well, W3C has released a new way to specify the legal contents of an XML file called XML schema In addition, XML schema also allow us to specify the range of values and data types of an element Example of XML schema for TicketRequest.xml

Questions and Discussion

Homework for Extra Points Create a simple XML file with at least four tags in which at least two tags with attributes for your college Create an XML schema file that validates the XML file above Due: Wednesday, June 1, 2005 in the class