XML Document Structure

XML Documents are composed of set of "entities", that are identified by unique names. All documents begin with a "root" or document entity. All other entities are optional.

XML Documents have a logical structure. Logically, documents are composed of declarations, elements, comments, character references, and processing instructions, all of which are indicated in the document by explicit markup.

XML Declaration is included as the first line in the document. It defines the XML Version of the document. In this case the document is of 1.0 version.

XML groups information in hierarchies. The items in the document relate to each other in parent/child and sibling/ sibling relationship.

Root element: First element of the document is called Root element. This element is the "the parent" of all other elements.

XML Tree starts at the root and branches to the lowest level of the test.

<root>
<child>
<subchild>...</subchild>
</child>
</root>

The terms parent, child and sibling are used to describe the relationship between elements. Parent elements have children. Children on the same level are called siblings (brothers or sisters).


All XML documents must have a root tag.

XML structure is called tree, and any parts of the tree that contain children are called branches, while parts that have no children are called leaves.

XML Element

Elements are the basic unit of XML content. Syntactically, an element consists of a start tag, and an end tag, and every thing in between.

The start tag consists of a name surrounded by angle brackets. The end tag consissts of the same name surrounded by angle brackets, but with a slash preceding the name.

XML defines the text between the start and end tag to be "character data"

XML Comments

If you want the processor to ignore and if you want to put character data in your document, then we use XML Comment tag.

Syntax XML Comments

<!-- This is a comments -->

Rules that needs to be remembered for writing the comments

1. You should never have "-" or "--" within the text of your comment, as it might be confusing the XML processor.
2. Never place a comment within a tag.
3. Never place a comment before the XML Declaration

XML Introduction

XML stands for Extensible Markup Language. XML is designed to describe data. XML tags are not predefined, you can define your own tags.

XML is actually a meta languague - a language for describing other languages - which lets you design your own markup languages.

XML is sometimes referred to as 'self-describing data' because the names of the markup elements should represent the type of content they hold.

XML Document example

<?xml version="1.0">
<employee>
<name>akhila</name>
<rollno>501</rollno>
</employee>

Common Uses of XML

1. Information Identification

Since you can define your own markup, you can define meaningful names for all your information.

2. Information storage

XML can be used to store textual information across any platform.

3. Information structure

XML can be used to store and identify any kind of (hierarchical) information structure especially for long, deep, or complex document sets or data sources, making it ideal for information management back-end to serving the Web.

4. Publishing

XML has the benefits of robut document management and control (with XML) and publish to the Wen (as HTML) as well as to paper (as PDF) and to other formats (eg., Braille, Audio, etc) from a single source document by using hte appropriate stylesheets.

5. Messaging and Data Transfer

XML is very heavily used for enclosing or encapsulating information in order to pass it between different computing system.

6. Web Services
Because of its use in browsers, machine processable data can be exchanged between consenting system. Weather services, e-commerce sites, AJaX sites and thousands of other data-exchange services use XML for data management and transmission.

7. e-Commerce
Companies are discovering that by communicating via the Internet, instead of by more traditional methods (such as faxing, human-to-human communication, and so on) they can streamline their processes, decreasing costs and increasing response times. Whenever one company needs to send data to another, XML is the perfect format for exchange.

8. Distributed Computing
XML can be used as a means for sending data for distributed computing, where objects on one computer call objects on another computer to do work. There have been numerous standards for distributed computing such as DCOM, CORBA, and RMI/IIOP, but as using XML and HTML through web services and/or SOAP enables this to occur even through a firewall.