XML stands for Extensible Markup Language.
In short, it is a text-based format for different systems to present structured data to each other. Structured data means the data describes the characteristics of some sort of hierarchy. An example of hierarchical data is a company that has a name and multiple employees that each have names and phone numbers. A list of the company and its employee information could easily be represented with XML. Here is how that might look:
XML is whitespace insensitive, meaning that any spaces or newlines are ignored, and (if present) are only for aiding human interpretation of the text.
XML is "extensible" because it is a language that allows you to extend and customize it. Languages that are based on the XML standard include XHTML, Atom, RSS, and ODF.
xml is a flexible way to create common information formats and share both the format and the data on the World Wide Web, intranets, and anywhere.
XML stands for Extensible Markup Language which is a markup language
XML = the language used to encode text onto a website. The certain set of commands that govern text size, placement, spacing, etc.
Hotel booking system supports as many xmls as needed, but 4 to 6 xmls are considered as best option to get the variety of hotel inventories. GTA, HotelBeds, HotelsPro, Travco, Tourico, Jac Travels, Darina Holidays, Sun Hotels and Jumbo Tours provide good inventories at great rates.
I hope you are aware of XML sitemaps. They are not for the user; rather these are especially crafted for the Search Engine Bot to index your pages. You can create a set of XMLs if you want. After you create these XML site maps you need to create a Google Web Master tools account and submit the site map. But if you don't want the user to click a link to reach the PDF then what use is it for? It is not fair practice to optimize for the bot and keeping the user away. It smells fishy to Google. So watch out.
MS-Win-XP(your words) :), actually have IE(internet explorer), made for rendering XMLs. For previewing purpose, its hard to have anything else, some xml editors, you can use a site mentioned below. "http://www.w3schools.com/xml/tryit.asp?filename=tryxml_dom_getelement" and if you want something like checking or editing or nodes, if u already have a valid xml, so try XML Notepad 2007, from Microsoft itself, which is much more refined. try the link below. http://www.microsoft.com/downloads/details.aspx?familyid=72d6aa49-787d-4118-ba5f-4f30fe913628&displaylang=en if still ur requirements doesnt meet, please feel free to ask.
For a standard Excel document, prior to Excel 2007, it is xls and xlsx is used in 2007. There are other kinds of files created by Excel, like templates which can be xlt or macros which can be xlm and xla for Add-ins, and there are other extenions. For 2007, you add x to the end of them.