12. Error codes

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"404 not found"

OK. You find an interesting site in your favorite directory. You click on the relevant link, and -- alas -- get an error code!

If you get the message "Document not found" when trying to open a webpage, do not despair. The message confirms that the site exists, and the webpage may still be there. If you look at a Web address like this one: http://www.pandia.com/search/faq.html, you will see that it looks very much like a file address on a PC or a MAC (cf. C:\documents\letter.doc or harddrive:documents:letter.doc).

As a matter of fact, an HTTP-address is a file address. http:// tells your browser to look for a webpage; www.pandia.com tells it to look for a server or computer called www.pandia.com; /search/ tells it to look for the directory (or folder) called "search"; and the last part tells it to open a file called faq.html that should be in that directory.

However, there is no directory called "search" on this server. You have been given an incorrect or out dated address. There may be a file with information about faq.html higher up in the file hierarchy, though.

So here's what you do: Delete the last part of the address until you come to the next "/". Then you are left with http://www.pandia.com/. Then hit "enter" and see what you get. If an address ends with a slash (/), you are not specifying what file the browser should look for.

Following the rules of the Internet, however, the browser will then look for a file that is defined as "default" by the server (normally called index.html or default.html). The main webpage or index in any directory is most often named -- you guessed it -- index.html. And there it is, http://www.pandia.com/index.html has a link to the Pandia FAQ.

Addresses on the Internet:

The server does not have a DNS entry

If your browser is unable to locate the server (the computer containing the webpage) this could mean that the server does not exist any more. However, it could also be that the server is down for maintenance or that the network is busy. In any case: Try again later.

If you have typed the address (URL), do check the spelling!

If everything fails, and you get the same error message the next day, you could visit Google at http://www.google.com/, a search engine that keep copies of the indexed webpages on their servers. You may find an old version of the file you are looking for there.

Yahoo! has more information on error codes: http://docs.yahoo.com/docs/writeus/error.html

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