Introduction to XML This is not an XML

Introduction to XML This is not an XML class, but for those who do not know XML, here is a very brief introduction…

What is XML? • XML is a standard published by the W 3 C • It is used to describe markup languages (“tag sets”) • It is application- and platform-independent • It handles multiple character sets (unicode) • It is a text format which is easy to read

How Does XML Work? • XML takes a stream of text characters, and allows them to be interpreted as a tree structure – It combines the properties of documents with the structure of object-oriented systems

Text Text = XML “element” Text = string, code, or number Text

XML Elements • XML elements have names, and a specific content which is described either in a DTD or (as for SDMXML) in an XML schema • XML elements can contain other elements, or values, or both (or neither) • They have a start tag <Name. Of. Element> and an end tag </Name. Of. Element> • They can have additional properties, called attributes: <Name. Of. Element Name. Of. Attribute=“Value. Of. Attribute”>

XML Elements (cont. ) • In an XML document, everything between an element’s start tag and end tag is contained in that element: <Elem. A> <Elem. B>Some Text</Elem. B> <Elem. C>Some Other Text</Elem. C> </Elem. A> • Here, Elem. A contains Elem. B and Elem. C, which in turn contain text.

XML Documents • XML documents have their exact contents (elements, attributes, numeric, string, and coded data) described in a separate XML file called an XML Schema • XML documents can be validated with a generic processor called an “XML Parser” • XML documents can be rendered into tree objects in memory, for processing, by many different software tools

Why XML is so Popular • XML is popular because: – it allows very complex sets of structured data to be transmitted over the internet as a simple stream of characters (a document), but… – It allows processing of that simple stream as a rich object model in the receiving application • XML is ubiquitous on the Internet, and is the basis of all web-services applications