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What is an XML Schema



? XML Schema Definition Language, XSDL, is used to enforce rules on data structures within XML files. The Schema Definition Language ensures that each object within the XML file conforms to a predefined structure as described within the XSDL document.

XML Schemas facilitate the creation of significantly complex data structures. Essentially, the XSD files themselves are simple files which would be legible to any basic programmer. They define elements within the object in terms of variables which have data types, such as string, integers and floating point numbers.

There are various XSD Editors on the market at present, the most obscure, yet well known is Microsoft Word. MS Word allows basic XML Editing, exporting, and even inclusion of XSDL Schema files so that you can check whether your document conforms to the correct standards.

There are other paid alternatives, which offer graphical XML and XSD Editing, for more hands on development tasks. For tasks which involve large amounts of XML Editing, I'd recommend purchasing some quality software. Bearing this in mind, you won't have to purchase any software if you're just getting started with XML, as you probably already have it.

If you're looking for a way to learn XML Schemas, search Google for some short tutorials, or purchase a book from somewhere like Amazon.

XML Style sheet Transformation Language XSLT is not the same as XSDL. XSLT is a transformations language which transforms XML Data to another format, such as HTML for web rendering. XSDL forces data integrity throughout this process, but will not alter data during this.

Schemas are actually XML Documents too, and they must conform to the legal boundaries of a schema specification, which is known as a 'schema schema'. Schemas themselves can be imbedded in the files, (for example XML, HTML). Now it has started getting complicated, the need for an XML Editor is apparent! Ideally, XML and XSD Editors are necessary for editing these files of modest complexity.

To understand schemas in detail, you really should do a little background reading in XML Prefixes and XML Namespaces. Again, reading on these can be found on Google (or Amazon if you're old school). XML Documents attach the URI of the Schema on the second line, by using the tag:

< Contact xsi:noNamespaceSchemaLocation="contact.xsd" xmlns:xsi = "http: / / w3.org/2001/X MLSchema-instance"> (without spaces)

In this example, the XML file would generally be about a set of contacts, with the root element being defined as a 'Contact' i.e. < xs:element name=" Contact">

Root elements are usually defined as complex type as they can contain numerous data types and objects within them. Within root elements, there is a 'sequence' of child objects. The available data types for these are; "element", "simpleType", "complexType", "date", "integer", to name just a few. Within XML Schema Documents, you may often see elements with a prefix 'xs:', or 'xsd:', this is a standard to define schema tags.


About Author Jamie Simpson :

Liquid Technologies produce a visual XML Editor. Check out their website at http://www.liquid-technologies.com , to Download XML now!


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Article Url: http://www.bharatbhasha.net/internet-and-computers.php/263684


Article Added on Friday, September 17, 2010
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Other Articles by Jamie Simpson

•XML Schema Design Best Practices
What is an XML Schema? An XML schema is an approach to describe an XML document containing data and other elements by providing specifications that are beyond to XML itself. A typical XML schema contains rules the elements should adhere to, the data type, its attributes, constraints and much more. Various languages such as Document Definition Type, Relax NG, XML Schema, Name Space Routing Language, Document Schema Definition Language, Schematron, SGML contribute to the design of XML schema on...

•What is an XML Editor
? An XML editor can help you create and edit valid XML documents more quickly and easier than if you rely on a general text editor to do the job. You'll always be able to do the same thing without an XML editor, but the editor provides some extra functionality that can help. At the simplest, the editor might offer syntax highlighting or coloring, to help you see the wood for the trees as you're navigating around your XML document. It might show XML tags, attribute names and values each in a...

•Why use XML
? XML Schemas describe the structure of an XML document. XML Schemas can be more powerful than any form of DTD (DocType Definition), and because of this, the web is evolving towards using XML Schemas more often than their DTD predecessors. XML Schemas also offer the support of namespaces, defining data types and are more extensible to further additions. XML Schema Language is also referred to by the name XML Schema Definition, or XSD for short. Like DTD's, XSD's are the legal base of the...

•The History of XML
XML in many ways set out to overcome the shortcomings of both SGML and HTML. SGML is a powerful and extensible language that has been used since the 1980's as a structured method of cataloguing and indexing data. SGML can be used to create an infinite number of mark-up languages, like XML can now do. SGML however is complex - unlike XML - especially for web uses. SGML is also expensive and currently unsupported in many web browsers as a mark-up language. Conversely, HTML is free and widely...

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