XHTML 1.0 is the W3C's first Recommendation for XHTML, following on from earlier work on HTML 4.01, HTML 4.0, HTML 3.2 and HTML 2.0. With a wealth of features, XHTML 1.0 is a reformulation of HTML 4.01 in XML, and combines the strength of HTML 4 with the power of XML.
XHTML 1.0 is the first major change to HTML since HTML 4.0 was released in 1997. It brings the rigor of XML to Web pages and is the keystone in W3C's work to create standards that provide richer Web pages on an ever increasing range of browser platforms including cell phones, televisions, cars, wallet sized wireless communicators, kiosks, and desktops.
XHTML 1.0 is the first step and the HTML Working Group is busy on the next. XHTML 1.0 reformulates HTML as an XML application. This makes it easier to process and easier to maintain. XHTML 1.0 borrows the tags from W3C's earlier work on HTML 4, and can be interpreted by existing browsers, by following a few simple guidelines. This allows you to start using XHTML now!
You can roll over your old HTML documents into XHTML using an Open Source HTML Tidy utility. This tool also cleans up markup errors, removes clutter and prettifies the markup making it easier to maintain.
Three "flavors" of XHTML 1.0:
XHTML 1.0 is specified in three "flavors". You specify which of these variants you are using by inserting a line at the beginning of the document. For example, the HTML for this document starts with a line which says that it is using XHTML 1.0 Strict. Thus, if you want to validate the document, the tool used knows which variant you are using. Each variant has its own DTD - Document Type Definition - which sets out the rules and regulations for using HTML in a succinct and definitive manner.
XHTML 1.0 Strict - Use this when you want really clean structural mark-up, free of any tags associated with layout. Use this together with W3C's Cascading Style Sheet language (CSS) to get the font, color, and layout effects you want.
XHTML 1.0 Transitional - Many people writing Web pages for the general public to access might want to use this flavor of XHTML 1.0. The idea is to take advantage of XHTML features including style sheets but nonetheless to make small adjustments to your mark-up for the benefit of those viewing your pages with older browsers which can't understand style sheets. These include using BODY with bgcolor, text and link attributes.
XHTML 1.0 Frameset - Use this when you want to use HTML Frames to partition the browser window into two or more frames.
The complete XHTML 1.0 specification is available in English in several formats, including HTML, PostScript and PDF. See also the list of translations produced by volunteers.
See www.w3.org/MarkUp/
XML is the Extensible Markup Language:
It is designed to improve the functionality of the Web by providing more flexible and adaptable information identification. It is called extensible because it is not a fixed format like HTML (a single, predefined markup language). Instead, XML is actually a `metalanguage' --a language for describing other languages--which lets you design your own customized markup languages for limitless different types of documents. XML can do this because it's written in SGML, the international standard metalanguage for text markup systems (ISO 8879).
XML is intended to make it easy and straightforward to use SGML on the Web: easy to define document types, easy to author and manage SGML-defined documents, and easy to transmit and share them across the Web. It defines an extremely simple dialect of SGML which is completely described in the XML Specification. The goal is to enable generic SGML to be served, received, and processed on the Web in the way that is not possible with HTML. For this reason, XML has been designed for ease of implementation, and for interoperability with both SGML and HTML. XML is not just for Web pages: it can be used to store any kind of structured information, and to enclose or encapsulate information in order to pass it between different computing systems which would otherwise be unable to communicate.
XML is an abbreviated version of SGML, to make it easier for you to define your own document types, and to make it easier for programmers to write programs to handle them. It omits all the options, and most of the more complex and less-used parts of SGML in return for the benefits of being easier to write applications for, easier to understand, and more suited to delivery and interoperability over the Web.
It removes two constraints which were holding back Web development:
1. dependence on a single, inflexible document type (HTML) which was being much abused for tasks it was never designed for;
2. the complexity of full SGML, whose syntax allows many powerful but hard-to-program options.
See www.ucc.ie/xml/
In other words, XHTML is simply an extension or a furtherance of HTML, whereas XML is a language for describing other languages--in other words, a style sheet for various languages, where one can modify various markup languages as one marks-up HTML via a cascading style sheet. This has far reaching implications, considering that once XML is learned, it could be applied to any number of languages or applications (conceivably even desktop applications, such as those found in Microsoft Office, or Corel Office Suite) in the same manner.
My sources for material, (much of which is direct quotes from technical pages):
XHTML-See www.w3.org/MarkUp/
XML-See www.ucc.ie/xml/
Also see:
XML vs. XHTML
10 points of xml
And for a very interesting slide show, see this slide show .
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This page was created by Gary Roll, for a discussion in differences in XHTML and XML.