XML is great for holding and communicating data between diverse systems along with browsers, it is completely platform independent this also makes it well suited for storing and transporting data across the internet.
By the use of an example concerning how adaptable and extremely versatile XML is, you are able to connect with web services by using say a Microsoft .net framework using a UNIX system written in C. However, in order for it to work you require a blueprint that will explain to both systems, the construction of the xml data or document, typically this is by way of some kind of schema or dtd.
The schema or dtd will probably specify the composition or layout of the xml file so that it can easily be read or parsed with the receiving system, eventually xml is a meta language so can not accomplish this specific function on it's own.
There's two main advantages to this, the first is that this means that your data will make it beyond the parsing phase as the construction has already been agreed and that helps you to get rid of any data that is not supposed to be there. The second thing is, it’s simpler for developers to understand what can be obtained as the protocol standard is documented.
About DTD, Document Type Definition
DTD is short for document type definition and as previously stated, the a means of telling other systems design and makeup of the xml file, in order for the acquiring system knows what to expect and thus it can easily interrogate the acquired xml data to verify that what is received is actually what is expected.
For example, the dtd will specify the elements which are being contained in the document and the attributes of the elements, as well as the ordering and nesting of those elements.
The dtd is called in or bundled by a development expression known as “declared”, the dtd is declared using what known as a DOCTYPE declaration beneath the XML declaration inside the xml document.
The dtd can be included inline or externally, inline as the name signifies is inside the xml document itself, in contrast to an external is outside of the xml document.
You will find advantages and drawbacks to both methods however inline is better should your documents are going to be saved and made use of offline.
About XML Schemas
Xml schemas are an advancement around the dtd method and for that reason widely thought to be a greater and a lot more potent method, in actual fact schemas also are xml files with their own DTD and do the job by referencing the XML Schema Namespace
XML Schemas supply a group of basic types, they include most basic computer programming types such as integer, byte, string and floating point numbers, but they also expand into Internet data types which include ISO country and language codes (en-GB for example).
The author of an XML Schema then uses these core types, along with various operators and modifiers, to create complex types of their own. These complex types are then used to define an element in the XML Document.
