XML is a mark-up (or "markup") language, so its uses with data are abundant. The key to understanding XML within Excel is first thinking about what a markup actually is. Imagine you have reams and reams of data relating to your customers. You might have their name, address, how much they owe you on invoices, and so on. How would you sort it out, file it, or in other words, mark it up? You'll probably start with surname in alphabetical order, invoices due in chronological order, and other logical patterns. This is all part of "marking up", and it's something XML does for you within Excel. Learn to manipulate XML, and you open up brand new ways of using your data not only in spreadsheets, but in other Office programs that are also compatible with XML.

If you already have a basic understanding of html, the way XML is written will be familiar to you. It uses 'tags' - pieces of information within angle parentheses. Within these parentheses, XML code gives a descriptive name to the data. In the above example, your data for each customer might start with Steven Jones inside the XML Name tags, followed by a new description for address, postcode, and any other information. This gives a whole new portability to your data. You could use the NAME XML data and import it into Word along with the address data, to create a mail merge advert to be sent to all existing customers.

The accountant and his or her own software is also likely to be able to import other XML data such as outstanding invoices or debts, so they can easily get a picture of how the books are looking. These are very simple examples of how XML data can be marked up and then moved, but its uses are far more varied. A caveat, though, the data must be well written - that is, if you omit something like a closing parenthesis or closing tag, the data within it won't work. Human error is responsible for most XML data not "working" in other programs, so check yours carefully for any glitches, typos or mistakes.

Schemas are a more complex way of validating your data. It has a set of inbuilt rules that 'know' how the XML data is supposed to look and will reject any incorrect entries. For example, you could write a schema that knows that a name field will usually be no more than three words (someone's first, middle and surnames). If a hasty secretary starts typing in the address instead, it will flag it up. Another example is that only numbers, and not words, should be entered in any monetary data such as the outstanding balance. If the schema keeps this rule, then your accountant will only receive correct numerical data and not a mixture of words and numbers, depending on who input it.

This is just a basic introduction to how XML can be used with your Excel data, and more training will be needed in order to learn the language fully and start integrating it into your everyday use of data. To get started, though - you need to activate it in Excel 2007 by clicking the Office button, then Excel options, then personalise. Then under 'developer', you'll see the tools for using XML. Why not have a play around, and see how far and flexible your data can go?