XML – An Introduction XML is getting a lot of attention right now, because of it leverages existing internet infrastructure and also because it enables the next generation of web applications to be deployed. There is a lot going on regarding XML that could be of interest to us in the near future, especially SOAP/.NET from Microsoft.

What Is XML? Extensible markup language Encoding objects based on their structure and meaning of content Convergence of three technologies: Document markup Data interchange World wide web XML is the next generation language for the web. An open standard maintained by the World wide web consortium. Application independent data structure for machine to machine data exchange. Provides deep structural capabilities to information owners. Based on SGML – standard generalized markup language. From SGML perspective, XML is a profile. Valid XML = valid SGML Extensible Markup Language (XML) is the universal language for data on the Web. It gives developers the power to deliver structured data from a wide variety of applications to the desktop for local computation and presentation. XML allows the creation of unique data formats for specific applications. It is likewise an ideal format for the server-to-server transfer of structured data. Convergence: the document centric world. WWW and HTML today. Human readable, Linear, Portable, based on conventions. the “data-centric world”. B2B, B2C. Managed data, predictable structure, data management, information location and retrieval, sorting and filtering, types links, separation of processing from storage. Web. The new world. Universal addressing mechanism, simple but rich transfer protocol, link resolution infrastructure, browser interface.

Why XML? To address HTML limitations Enabling technology for a business web Next generation web HTML provides simple formatting and access to non-text objects. Too flat, too display oriented. HTML is primarily a formatting language. Business is done over the web. Data interchange. Meta-data. B2B. Better access to web-based information. Structured. XML will make web content more information oriented. Internationalized (Unicode). Rendering (Cascading Style Sheets, XSL – Extensible style sheet language). Addressing and linking (XML Query, Xpath, Xpointer, Xlink). Manipulation (SAX, DOM APIs). Multimedia (SVG, SMIL). Metadata.

Basic XML Process XML Document End Result Content, structure, meaning XML Document End Result Processing Engine What to do with XML Application SpecificationObject XML Processing Store it – file system, database (BLOB or data type), XML aware database as decomposed tree or as cluster of objects and relationships. Send and Receive it – Spit it out of my application, send it over the wire, pull it from the data store. Transform it – Transform to industry standard schema, display based vocabulary, down translation. Render it – XHTML, PDF, RTF, PostScript, Text, XSL Formatting objects, CSS Two step process – XML Parser & application layer.

Processing XML Parsers Parsers are commodity items Two basic types: Tree based (DOM) Event based (SAX) Your applications requirements decide which one to use Validating parsers Document Object Model W3C. Tree structure to create, access and modify XML document representation. DOM is specified in IDL. Simple API for XML – GUIs, stream based processing. SAX Implementations are available in Java, C/C++, Perl, COM, Python, Build and populate internal data models from XML documents, pull in XML data streams, do pipeline processing of XML documents. Xt, an XSLT engine uses SAX. Well formed documents need not be valid. Applications need data to be predictable.

XML Validity Well-formed is not always enough. Provides higher level conformance. Include formal definition of data model. Document type definition (DTD). Schema. A DTD defines a document type. Well-formed Vs Valid Well formed documents can be processed ny SAX or DOM, but applications need data to be predictable. All constructs used in the document must be defined. DTDs have been around for years. Stable W3C spec. Existing tools that understand and use DTDs. Schemas are an attempt to provide alternate to DTDs. Schema itself is a well-formed XML. Processable as XML. XML-Schema (Microsoft), SOX Commerce One, DDML/Xschema Schema supports data typing for attribute values. Enforces parser data typing. A DTD is a set of declarations that define a document type Each XML is an instance of its document type.

XSL and XSLT XSL XSLT XSLT – transformation stylesheet XSL FO – formatting objects XSLT XSL Style sheets are well-formed XML documents XSLT takes as input a well-formed XML document produces as output XML, HTML or non-XML XML Document HTML Document XSLT Engine XSLT Style sheet

Very Simple Example <xsl:stylesheet version=“1.0”> <person type=“fictional”> <name> <first>Peter</first> <last>Pan</last> <feature>flies</feature> </person> <xsl:stylesheet version=“1.0”> <xsl:template match=“person”> <html><p> <xsl:apply-templates/> </p></html> </xsl:template> </xsl:stylesheet> XSL Style sheets are well-formed XML documents XSLT takes as input a well-formed XML document produces as output XML, HTML or non-XML\ The Key to XSLT: Addressing Must be able to tell what elements a template would be used on, therefore must be able to identify elements in a document by : name : location : parentage : attribute : attribute value : content W3C provides standard way to do this: Xpath XSLT Engine <html><p>PeterPanflies</p></html>

XML Future Http & XML =. XML enabled data bases. Soap. XML-RPC. Can work across firewalls. Platform independent. XML enabled data bases. XML enabled search engines. Industry standard XML vocabularies. SOAP – Simple object access protocol Many of the top SGML vendors have made generalized XML versions of their products available, such as ArborText Adept7 (http://www.arbortext.com/), Inso Dynabase (http://www.inso.com/), Chrystal Software Astoria (http://www.chrystal.com/), and POET Object Server (http://www.poet.com/) for authoring, editing, and database publishing. Other vendors, such as DataChannel Inc. (http://www.datachannel.com/) have products based on XML for data management XML vocabularies are the elements used in particular applications or data formats—the definitions of the meanings of those formats. For example, in CDF, element names such as <schedule>, <channel>, and <item> make up the vocabulary for describing collections of pages, when these pages should be downloaded, and so on. Vocabularies, along with the structural relationships between the elements, are defined in XML DTDs or XML schemata. Users can even build their own XML vocabularies (hence the "Extensible" in XML). An automotive trade group, for example, could build a specialized XML vocabulary of automotive terms, and then tag its data with those terms. Microsoft is working with various industries to help them create their own XML vocabularies, Denning says. Standard Vocabulary We expect standard libraries of vocabulary to be developed to capture common semantics used in vertical applications and particularly in industry and application domains. Dublin Core and CDF are two examples of such standard libraries. CDF - Channel Definition Format (CDF) is an XML-based data format used in the Microsoft Internet Explorer version 4.0 browser, for describing Active Channel content and the Desktop components. Open Software Description (OSD) is an XML-based data format fully supported in Microsoft Internet Explorer version 4.01, for advertising and installing software components over the Internet. Open Financial Exchange (OFX) is a data format that Microsoft Money and Intuit Quicken personal finance applications use to communicate with financial institutions over the Web. Although it is currently described using SGML, OFX will soon be based on XML.