An xml schema is a data file that's intended to explain the contents of an xml document as well as dictate and lay down rules to what can and cannot be contained in the xml file. These constraints are not just restricted to syntactical rules but can also specify what elements should be included, the order of these elements and child elements and so on.
Normally, an XSDL or XML Schema Definition Language is employed to apply these rules on data elements within an XM file.
An XML Schema is therefore incredibly helpful and versatile, allowing you to create very intricate and detailed data elements by specifying which elements inside of your data objects you may include or ought to include in your xml file, such as the string, integers etc.
A significant thing to be aware is the fact Schemas are also xml documents therefore they will also have to be valid and in accordance with normal syntax and other rules of xml as well, also referred to as a schema specification or even schema schema.
Additionally, there are additional meta languages that have been created solely to convey XML schemas, such as DTD, XML Schema and Relax NG. The latter two are a lot more developed and expressive than DTD, which happens to be actually rather limited with regard to capability.
To basically hook up your XML schema to your XML file (for validation functions as well as check the XML file is as per the specifications specified by the XML schema, the precise method depends on the schema language that you employ, one example is it could be as simple as calling in the schema from inside your xml file ie by adding the path via markup, generally known as imbedding or it could be via some other exterior method ie an xml schema validator, which might also be an online tool or even a computer's desktop based application.
To work with and change your XML schemas, you are able to use any of the free, open source and commercial XSD Editors that are available. These are typically available in a range of calibres, begining with the very basic and unimpressive functionality and feature sets, to some of the high end editors which feature graphical xml / schema representation and editing, along with syntax highlighting and source / wysiwyg view.
For minimal xml work, notepad or notepad , both available for free are more than up to the task, however, for more intense xml work, particularly development and professional xml coding, you should look at utilizing a commercial xml / xsd editor which will help you improve your development time and lessen errors in your code.
If you would like learn more about xml schemas or have an interest in finding sample xml schemas, think about reading a more advanced and comprehensive xml schema guide including the one here, http://www.liquid-technologies.com/Tutorials/XmlSchemas/XsdTutorial_01.aspx, or perhaps check out wiki or the w3c website.
The W3 schools webpage provides some good training for beginners however if you happen to be more advanced or intermediate programmer this website is just not for you because material is actually really simple and easy targeted at newbie learners.
