1. Are there advantages of xhtml over traditional html?
The main advantage is probably that the language is extensible meaning that the user can extend it's capabilities. Another advantage is that an XHTML document can be reformatted for use on different display devices such as cell phones and PDA's. Also because it is a stricter language it makes it easier for browsers and search engines to interpret the markup.
2. Are there disadvantages?
There are very few. About all I can think of is that it forces us to be more disciplined and write well formed mark-up but we (webmasters) were doing that anyway.
3. What is XML, why should you and I care?
Extensible Mark-up language originated from SGML (standard general markup language). Whereas XHTML and HTML define what information looks like XML describes what information is. You get to detemine the elements yourself with customizable tags. It is a much stricter version of HTML.
4. What is a DTD? And why should you and I care?
Document type declaration or DTD is declared at the top of a document in the DOCTYPE section of an HTML or XHTML page. It defines the rules for the markup of the document. More specifically it defines the elements and attributes that you are permitted to use in that type of document.
5. Provide 4 examples of XML based languages.
Four examples are: RSS (Really Simple Syndication), Scalable Vector Graphics, OFX (Open Financial Exchange) and MusicXML.
RSS - is a popular XML application for news feeds.
Scalable Vector Graphics - It is used for descibing 2-d vector graphics. It includes three types of objects. They are vector based graphic shapes, rasterized images and text.
OFX - It is for exchanging financial information. It is used by the banking industry.
MusicXML - It is an XML based language designed for the exchange of musical scores by scorewriters.
6.What does "well formed" mean to XML?
It means that the document conforms to the XML syntax rules. The rules are that the document must have a root element, all elements must have closing tags, that the tags must all be lower case, that the elements must all be nested and that attribute values must be quoted.
7.What does valid mean to XML ?
A valid XML document means that it is well formed and also that it conforms to the rules of a specific DTD.