XML & webservices Ayush Agrawal B.E. Fourth Semester C.S.E. A
EXTENSIBLE MARKUP LANGUAGEstore and organize just about any kind of informationAn open standardUnicode as its standard character set , so supports in writing anytype of script and symbolclear, simple syntax and unambiguous structureCan be combined with stylesheets to create formatted documents
What Is XML?XML is a protocol for containing and managing information.Family of technologies that can do everything from formattingdocuments to filtering data.Necessary foundation for the next levelSatellite technologies such as stylesheets, transformations,and do-it-yourself markup languages.
FACTS • Xml is different from Html.1 • In Xml we can create our own2 tags . • It is a W3C recommendation.3
XML TREEXML documents must contain a root element. This element is "the parent" of allother elements.The elements in an XML document form a document tree.The tree starts at the root and branches to the lowest level of the tree.A general view
SYNTAX AND RULESALL ELEMENTS MUST HAVE CLOSING TAGS.ALL TAGS ARE CASE SENSITIVE. ELEMENTS MUST BE PROPERLY NESTED. ATTRIBUTE VALUES MUST BE QUOTED. ENTITY REFRENCES SHOULD BE USED. WHITE SPACES IN A DOCUMENT ARE NOT TRUNCATED.
XML ELEMENTS An element can contain: An XML element is everything from 1.other elements (including) the elements start tag to 2.text (including) the elements end tag. 3.attributes or a mix of all of the above...XML elements must follow these naming rules:1.Names can contain letters, numbers, and other characters2.Names cannot start with a number or punctuation character3.Names cannot start with the letters xml (or XML, or Xml, etc)4.Names cannot contain spaces XML elements can be extended to carry more information.
XML VALIDATION AND VALIDATORA "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD) <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE note SYSTEM "Note.dtd"> The purpose of a DTD is to define the structure of an XML documentThe W3C XML specification states that a program should stop processing an XML document if it finds an error To validate xml files we can use various validators because with xml errors are not allowed
VIEWING XML FILES Raw XML files can be viewed in all major browsers. Dont expect XML files to be displayed as HTML pages. The XML document will be displayed with color-coded root and child elements A plus (+) or minus sign (-) to the left of the elements can be clicked to expand or collapse the element structure To view the raw XML source (without the + and - signs), select "View Page Source" or "View Source" from the browser menu.
WE CAN LINK XML FILE WITH A CSS FILE TO ADD DISPLAY INFORMATION TO A XML FILE INCUDE JUST A LINE: <?xml-stylesheet type="text/css" href=“filename.css"?> WE CAN EVEN USE XSLT TO PLAY WITH THE DISPLAY OF A XML FLEXSLT (eXtensible Stylesheet Language Transformations) IS THE RECOMMENDED STYLE SHEET LNGAGE FOR XML FILE Different browsers may produce different result when transforming XML with XSLT. To reduce this problem the XSLT transformation can be done on the server.
NAMESPACES Namespaces provide a method to avoid element name conflicts. In XML, element names are defined by the developer.This often results in a conflict when trying to mix XML documents from different XML applications. <table> Name conflicts in XML can easily be <tr> avoided using a name prefix. <td>Apples</td> <td>Bananas</td> <h:table> </tr> <h:tr> </table> <h:td>Apples</h:td> <h:td>Bananas</h:td> <table> </h:tr> <name>African Coffee Table</name> </h:table> <width>80</width> <length>120</length> <f:table> </table> <f:name>African Coffee Table</f:name> <f:width>80</f:width>The namespace is defined by the <f:length>120</f:length>xmlns attribute in the start tag of an </f:table>element.The namespace declarationhas the following syntax. xmlns:prefix="URI".
Web services• The basic standards for web services are:• XML (Extensible Markup Language)• SOAP (simple object access protocol)• WSDL (web services description language)• UDDI (universal description, discovery and integration)
• Web Services involve three major roles – Service Provider – Service Registry – Service Consumer • Three major operations surround web services – Publishing – making a service available – Finding – locating web services – Binding – using web servicesBecause web services deals with inter-organisation communicationthese must be universal standards.
SOAP• Actually used to communicate with the Web Service• Both the request and the response are SOAP messages• The body of the message (whose grammar is defined by the WSDL) is contained within a SOAP “envelope”• “Binds” the client to the web service
WSDL• Describes the Web Service and defines the functions that are exposed in the Web Service• Defines the XML grammar to be used in the messages – Uses the W3C Schema language
UDDI• UDDI is used to register and look up services with a central registry• Service Providers can publish information about their business and the services that they offer• Service consumers can look up services that are available by • Business • Service category • Specific service