The World Wide Web is made up of many different types of computers, using different operating systems. In order to access files on a variety of computers, we need to use names that are acceptable on all of them.

This means we're reduced to the "lowest common denominator" of file names - simple names avoiding characters (letters, numbers, and symbols) that have special meanings on certain computer systems.

In this module, we'll also discuss "special" file names on the Web - names that are used for specific, predefined purposes. And we'll discuss the file extensions, the 3 or 4 letter abbreviations at the end of the name like htm or jpeg.

You can use:

• alphabetic characters abcdefghijklmnopqrstuvwxyz
• numeric characters 0123456789
• the dash -
• the underscore _
• the dot . (or period) to separate the main part of the name from the extension.

Keep your names under about ten characters in length. You can usually get away with more, but it's better to keep it simple, and the longer it gets the more likely a computer somewhere on the Internet will choke!

Notice that capital letters don't appear in the list above. You can use them, but unless you're careful, they can cause a lot of confusion.

Why? Because some computers are case-sensitive and others aren't.

• On case-sensitive systems, like Macintosh OS-X, Unix and Linux, these names are all different:
  home | Home | HOME
• On case-insensitive systems, like DOS, Windows, and Macintosh OS-1 through OS9, these names are all the same:
  home = Home = HOME

Bottom line:

To keep your life simple, avoid capital letters.

Caution: Capital letters can be a problem with MS Windows. Although Windows doesn't care about capitals vs. lowercase letters when it looks for files, it sometimes automatically capitalizes the first letter of a file's name when it saves the file for the first time! This can cause much frustration when you create links using lowercase letters. They work just fine when you test them on your Windows computer, but you find that on the server the links no longer work!

To avoid this problem, check the names of Web files and graphics on your computer using Windows Explorer or My Computer. If you find a file with a capital letter, click the name twice slowly to edit it, and change the capitals to lower case. Once changed, they (generally) stay that way.

There are thousands of symbols available for writing inside files, but they should all be avoided in Web file names. The only two symbols you can use with confidence are the dash and the underscore shown above.

The biggest trouble-maker is the space character. This character is OK on some systems but not on others, so the best thing to do is:

Just Say NO to SPACES!
in Web file names

The home page can have any of these names:

• index.htm 
• index.html
• default.htm
• default.html

What does "being a home page" mean?

A Web server is often given a URL with only a server name or a directory name, for example:

www.wccnet.org
www.wccnet.org/dept/cis/

What if the server can't find any of these, but the directory exists? It's then programmed to give you a directory listing of the files in that directory; it's even linked so users can click on any listed file or directory and get it on their screen! But as a Web site designer, you will probably want to avoid giving your guests a directory list! It's rather like coming to an apartment building and finding a locked door with a row of labeled buttons to push. You hope someone is home! 

On the Web, it's much nicer to enter by a well-designed and attractive home page!

Note: in class, your instructor may ask you not to create a file with the name index or default. This is so your directory structure is available for inspection and to help you debug your assignments.

The extension is the part of a file name after the dot. It indicates what type of file the name belongs to. On most computer systems, the extension is used by the software decide how to process a file.

The common extensions for (X)HTML Web files are .htm and .html. For simplicity, always use one or the other; shorter is better!

Common Extensions found on Web files

How Windows' Simplicity makes life complicated

MS Windows provides two similar tools for organizing your files: "My Computer" and "Windows Explorer" (not the same as "Internet Explorer"!).

Using off-the-shelf Windows, these two tools both hide file name extensions, but show icons related to the types of files. Presumably this is done to simplify the life of beginning computer users.

Problem: when Web developers refer to a file with a link or image tag, they must know the extension - not just what type of file it is. So the "simplicity" of Windows' tools makes your life difficult. This is particularly true for HTML and JPEG files, whose extensions have more than one possible spelling.

Solution: in either "My Computer" or "Windows Explorer", select the Tools menu's Folder Options... (see Figure 1).	Figure 1
In the Folder Options dialog box, click the View tab. In the Advanced Settings window, click to un-check the option, "Hide file extensions for known file types."	Figure 2

Recommendations for Web developers using Windows:

• Use "Windows Explorer" rather than "My Computer": it has a folder-tree diagram which can help you visualize where your files are in relation to one another.
• View files in details-view: you can see the sizes and creation dates, and sort on them to locate files that are either recent or old, large or small. (In Windows XP, thumbnail-view can also be helpful for visually locating files.)