There might be thousands of telephone numbers of 545-321.When we add an area code and, perhaps, an international code, we make the number unique: 44 020 545-321.
We can see clearly that there is a catalogue containing CDs, each of which contains some tracks (music aficionados will notice that I have cut down the track listings for space! You can also see that XML can be less efficient than some other file formats.
Yet, in many cases, the loss in efficiency that results from the increased size can be made up by the speed of processing a well-defined XML file, as parsers (programs that read XML) can predict the structure.
We therefore define attributes of the element in the form attribute="value".
Once you have produced your own set of elements and structures, these formats can be referred to as dialects. With so many different dialects floating around, conflicts of meaning can easily arise.
The structure of the catalogue is such that it contains CDs, which in turn contain tracks.
This is our hierarchy, and will be important later, when we need to parse the document.This describes what is meant by "interoperable file format" — once you produce an XML file, it is open to everyone.An input, and all the information required to understand the structure of your data, is included in the file. Here’s a text file and an XML file that both store the same information: Notice how the subject of our data is defined in the XML file.The way we'd interpret the plain text file would be dependent on how we designed our own format.No information exists to tell others what the actual data means, its order, or how to parse (read) it in other projects.One of the most exciting recent advances in computing has been XML. Before we look into the specifics of XML, it is important to know why XML exists and where it can be used.