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XML (eXtensible
Markup Language) is a method for putting structured data in a text file.
Although
an XML document superficially resembles an HTML document in that they
are both the product of a markup language that uses tags, that is where
the similarity ends. XML overcomes the common pitfalls of unstructured
markup languages, of which HTML is the most widely used.
XML produces
files that overcome ambiguity, lack of extensibility, lack of support
for internationalization/localization, and platform-dependency.
XML is
often called a meta-markup language, and that is because XML tags are
used differently than those in convential markup languages. Whereas
<p> means paragraph in HTML, <p> in XML could mean anything
depending on the stylesheet that is used to translate the XML. Therefore, tags
delimit pieces of data in order to structure it appropriately, but leave
the interpretation of the data completely to the application that reads
it.
The rules
of XML syntax are much stricter than for HTML. In HTML, forgotten tags
or attributes are tolerated. But the official XML specification prohibits
second-guessing the meaning of a broken XML file; if the file
is broken, an application has to stop and issue an error.
XML files
are text files. As such, they are larger than equivalent binary files,
but they can be easily compressed. XML files are not intended to be
human- parsable the way HTML file are, but they are readable for purposes
of debugging, for example.
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