Credit: Jon A. Morse (ST Sci/NASA)
The various Web languages have their distinctive roles in managing
information on the Web:
- HTML is a language that lets you control how
information is displayed and presented on the Web: place an image
here,
make this text large, color this background blue, etc. It is
entirely concerned with appearance as opposed to content or
meaning
- JavaScript is a general purpose programming
language that lets you control and program the actions, placement,
and properties of almost any HTML element, and locate, add, delete,
or change any XML element. JavaScript can control the appearance
of information on the web as well as its content
- XML is a user-defined hierarchical database
containing
elements and attributes. It stores information that may
subsequently be displayed on the Web, but contains no information
whatsoever on how that information is to be presented. It is all
about content as opposed to appearance
- XSL is special purpose programming language
that transforms XML into displayable HTML, or to other forms of XML.
It can not only create many different Web pages from an existing XML
database, but
can also insert, delete, or modify XML elements as well
- Xpath is a very limited language that XSL
uses to identify structures in XML to be transformed into
HTML or XML. It consists largely of paths that identify portions
of the tree structure for a particular XML file, along with conditional
expressions that contain boolean operations, such as "and", and "or",
comparison operators, and string manipulation and other functions
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