www.getmyuni.com UNIT- III XML TECHNOLOGY FAMILY The Role of XML XML is a specification for defining new markup languages. XML is a metalanguage (literally a language about languages) defined by the World Wide Web Consortium (W3C), one of the main organizations driving the push to open Web standards. In its simplest sense, XML is a set of rules and guidelines for describing structured data in plain text rather than proprietary binary representations. However, as a phenomenon, XML goes beyond its technical specification. Since its standardization by the W3C in 1998, XML has been the driving force behind numerous other standards and vocabularies that are forging a fundamental change in the software world. XML is simple. Technically, it's a language for creating other languages based on the insertion of tags to help describe data. However, XML is actually more than just tags. To see what we mean by this, let's begin with a simple XML data description. XML is a combination of tags and content in which the tags add meaning to the content. The following is a simple XML markup of customer information. Start tags such as <Name> begin an element that contains the actual data. End tags such as </Name> mark the end of an element definition. <Customer> <Name>John von Neumann</Name> <PhoneNum>914.631.7722</PhoneNum> <FaxNum>914.631.7723</FaxNum> <E-Mail>[email protected]</E-Mail> </Customer> There are several important basic points to observe about these definitions. XML allows data to be stored in either elements or attributes. Elements and attributes can be named to give the data meaning. Start tags and end tags define elements that are the basis for XML tree-structured representations of documents. Elements can contain text data and/or other elements. The XML Advantage XML has had an impact across a broad range of areas. The following is a list of some of the factors that have influenced XML's adoption by a variety of organizations and individuals. XML files are human-readable. XML was designed as text so that, in the worst case, someone can always read it to figure out the content. Such is not the case with binary data formats. Widespread industry support exists for XML. Numerous tools and utilities are being provided with Web browsers, databases, and operating systems, making it easier and less www.getmyuni.com expensive for small and medium-sized organizations to import and export data in XML format. Major relational databases now have the native capability to read and generate XML data. A large family of XML support technologies is available for the interpretation and transformation of XML data for Web page display and report generation. The XML Technology Family XML is not just a technology for defining data vocabularies. Surrounding XML is a wide variety of XML standards and initiatives that act in combination with XML to address many of the issues associated with bringing XML into mainstream computing, namely presentation, structure, and transformation. As fig shows, the XML core includes XML itself, based on the XML 1.0 specification, and namespaces, the specification that allows XML documents from different sources to be combined and yet be able to disambiguate elements with the same name from different sources. Following is a list of other categories in the XML technology: Structure and data types: When using XML to exchange data among clients, partners, and suppliers, it's important to be able to define how XML documents should be structured. DTDs and XML Schema provide this capability. DTDs come out of the world of Standard Generalized Markup Language (SGML), focusing primarily on structure by specifying what elements and attributes are considered valid for a particular XML instance document. XML Schema is a more recent initiative of the World Wide Web Consortium (W3C) that puts a more conventional data processing spin on describing XML data with more precision than with DTDs. XML presentation technologies: In keeping with an important design pattern for robust systems, XML intentionally separates data content from presentation through the introduction of supporting technologies that focus on delivering content to users via a variety of devices and presentation media. Among the technologies for presentation are XHTML, a modular XML-conformant replacement for HTML; CSS for controlling the display properties of HTML or XML in Web browsers; XSL and XSL Formatting Objects (XSL-FO) for formatting XML for various output media; XForms for collecting data from Web forms and returning XML; VoiceXML, for delivering content to voice- enabled devices; and Wireless Markup Language (WML), for delivery to wireless devices enabled for Wireless Application Protocol (WAP). XML manipulation technologies: Manipulation technologies provide the capability to extract and transform XML in different ways. These technologies play an important role in server-based XML processing for business-to-business (B2B) data manipulation and exchange. XSLT is widely used to transform XML from one format to another; XPath is a technology used by other XML technologies to navigate through an XML tree structure and zero in on particular elements or subtrees; XLink is a technology for creating and describing links between resources and for enabling links that go beyond the simple unidirectional links of the current Web; and XQuery is an evolving technology for extracting and querying XML repositories. www.getmyuni.com Other related technologies: The XML family of technologies also includes initiatives for working with metainformation, which is literally information about the information contained in an XML document. Technologies in this space include RDF and InfoSet. The XML technology family. Structuring with Schemas A schema defines a data representation. "Schema" is a general term that describes the form of data. Originally the term was used to define the structure of databases. A schema is a formal specification of the grammar for a specific XML vocabulary. Schemas are useful in validating XML document content, determining whether the XMLhttp://csetube.tk/ document conforms to the grammar expressed by the XML Schema, and describing XML structure to others, which enables the exchange of structured information between collaborating applications or business partners in a platform- and middleware-neutral manner. In the XML world, there are two schemas: DTDs and XML Schemas. Figure illustrates how either may be used to define a family of XML document instances. DTDs focus primarily on structure, allowing an XML vocabulary designer to specify the elements and attributes that are appropriate for a set of XML instance documents. However, DTDs have limited capability to describe data types within an XML document. Both DTDs and XML Schemas may be used to define the structure of an XML document. www.getmyuni.com XML Schema is a newer technology, adopted by W3C as an official Recommendation in May 2001, intended to provide the kind of detailed structure often associated with programming languages' data types and useful in enabling solutions for the exchange of XML-based information where it is helpful to check data format accuracy before processing begins. DTD: DTD can be used by both the sender and receiver of a ZwiftBooks document. When ZwiftBooks publishes its DTD for a query, senders can use the DTD to create XML documents that the ZwiftBooks server will understand. On the receiving end, the server can compare an incoming XML document against the DTD and determine if the incoming XML data is valid with respect to the DTD. If not, it can return a message indicating an error in the incoming data format. www.getmyuni.com Figure shows how a DTD can be used by both the sender and receiver of a ZwiftBooks document. When ZwiftBooks publishes its DTD for a query, senders can use the DTD to create XML documents that the ZwiftBooks server will understand. On the receiving end, the server can compare an incoming XML document against the DTD and determine if the incoming XML data is valid withhttp://csetube.tk/ respect to the DTD. If not, it can return a message indicating an error in the incoming data format. There are several points to keep in mind: DTDs are written using a different syntax from XML. This is because DTDs were first developed in the SGML world before XML existed. DTDs define the elements and attributes that can validly appear in our ZwiftBooks XML documents. DTDs are not able to define distinctions about data types. For example, a DTD cannot declare that an element must contain a valid date or numeric field or even an ISBN number. A DTD is limited to declaring that an element must contain text; it cannot control what kind of text, as, for example, by distinguishing between numeric and alphabetic characters. www.getmyuni.com XML Schema The alternative to using DTDs to specify what constitutes a valid ZwiftBooks XML document is to use XML Schemas. The XML Schema Recommendation goes beyond the basic text-based descriptors provided by DTDs. It provides more detail about the kind of data that can appear as part of an XML document. Unlike the non-XML syntax of a DTD, XML Schema is itself an XML vocabulary that defines rules governing the structure and content of elements and attributes in an XML document. Because XML Schemas are XML, they can be processed and managed like any XML instance. XML Schemas take a giant step in moving XML from the document world into the data processing world. Schemas support a broad range of data types, and include useful features like range constraints that let XML authors describe bounds for data that can be enforced by schema processors. The advantage of using XML Schemas over DTDs is that XML Schemas eliminate the need for hand-coded data checking of XML data fields.