Schofield's first law of computing isn't really a law, and it is not widely observed, but it can certainly help you lead a better life. What it says, simply and obviously, is "never put data into a program unless you can see exactly how to get it out".
Computers - software and hardware - are transitory and cheap. Useful data is, by contrast, very expensive to create, and could last forever. So if you invest vast sums in creating data, then it is silly to let someone encrypt it and not tell you the key. Alas, that is what you are doing when you put your data into proprietary file formats such as Real's Realvideo, Sony's Atrac audio, Microsoft .doc files, and so on.
Sooner or later, you could end up with data files you can no longer read.
Ideally, try to use data formats that are published, open, not protected by patents, and royalty-free, such as HTML, PNG and vCard. In most cases you will have to compromise, but if you use formats where the specification has not been published, you risk making your data hostage to the supplier's fortunes. Even Macromedia's Shockwave Flash (.swf) format is published.
If the file format is open - or at least published and licensed on a reasonable and non-discriminatory basis - then there should be a wide range of applications that can be used to create and display that type of content. You won't be locked in to using a specific product. Open file formats therefore encourage real competition and promote choice.
Some of the benefits of this approach can be seen in, for example, the MP3 music world, even though MP3 is not open but patented, owned by and licensed on behalf of the Fraunhoffer Institute.
The idea of open file formats is not new, of course, but it may soon become much more important. If you want to know why, look at http://xml.openoffice.org/, the Web site for the open version of Sun's Staroffice. It concerns the XML Project, which is working to create a fully documented, open XML-based file format for office applications such as word processors and spreadsheets.
I hope other suppliers apart from Sun are planning to use this XML format too, because it is not good to have just a single company supplying a file format, even if it is truly open.
If every office suite could read and write XML-based files then you would be able to choose between them on merit. Schofield's first law would be satisfied and the world would be a happier place.
Jack Schofield is computer editor at The Guardian