1 File Directory Structures
By Eric Nakagawa
http://www2.hawaii.edu/~ericnaka/
1.1 Introduction
In today’s high-tech society, it is almost foolish to think people can exist without computers, and vice versa. We are dependent on the abilities a computer have provided us, but is it necessarily true that all the high-tech talk we hear designates from singular, complex ideas? The idea begs to differ. Because all computers need to access information, information computers need to access consists of data and programs, data and programs are stored in files, files help to keep information organized, but what keeps the files organized and what makes knowing about this technology important?
1.2 Background
Files on a computer are organized into what are called Directories. Directories provide a logical framework for computers and humans to both utilize data and programs. In computers, files are split up into a branching system consisting of links and nodes. This system of links and nodes look like an upside-down tree (Figure 1.2-1). In Computer Science, the term “tree” is used to refer to this structure. With regard to computer file organization, we use the term “root” to refer to top-most point of the directory structure (Figure 1.2-2). In addition, another way to refer to the “root” of a directory structure is to use the ‘/’ character. The ‘/’ character refers to whatever is designated as the root, so in the case of Figure 1.2-2, it would be “C:/.”
There are a few other terms necessary to understand directory structures. Two used when referring to the location of a file are “absolute” and “relative” locations. An “absolute location” means the location of the file from the root to the file, and all intermediary directories. For example, (Figure 1.2-2) the absolute location of “SC.EXE” is “C:\GAMES\STARCRAFT\SC.EXE.” A “relative location” refers to the location of the file relative to the directory the user or program is in. For example, (Figure 1.2-2) if a user were currently in “C:\STARCRAFT\” the relative path to the file “ERIC” would be “SCORES\ERIC.” Also, we generally use are two periods consecutively placed before a backslash (“..\”). In the English language, this stands for “up one level” or “up to parent1.” The two periods and a backslash – up one level – are used only when dealing with “relative” files. Since the “up one level” string, literally, means “one level up,” it can be used repeatedly2. Using the previous example from Figure 1.2-2, if a user were currently in “C:\STARCRAFT\SCORES\” it can be written relatively to “C:\WORK\DATABASE\README.TXT” using the “up one level” string like so, “..\..\WORK\DATABASE\README.TXT.” Computer File Directory Structures, although built using terminology and techniques—that some may find challenging or confusing—can be very useful, and when presented in a logical way can actually make sense.
Figure 1.2‑1
Figure 1.2‑2
1 A “parent” in Computer Science means “the node one level up”. A node with a “parent” is called a “child.” Many “children” can have one related “parent,” but no “child” can have two different “parents.”
2 Sometimes in Computer Science, it is possible to use the same, simple rule to execute commands in repetition. When dealing with a File Directory Structure, using the “..\” string can result in something called “recursion.” Recursion is a different approach to writing algorithms, by the fact that a “recursive” function, or method not only breaks apart a program into smaller easier managed pieces, but that it also calls on itself. Calling on itself, sometimes results in quicker performance of certain algorithms. Another more frequently used approach used in writing programs, is called iteration. Iteration refers to executing commands in succession usually until a test case is proved or disproved.
1.3 How this applies now
File Directory Structures are used in every type of computer around. Although not all computer Operating Systems, such as the popular Windows, Un*x, Linux, or Apple’s new OSX, use such a simple tree structure as presented above, it is still good to have an understanding of the technology. One reason for this, is that the Internet, although large and full of content, still uses a simple File Directory Structure. For example, when writing HTML pages or Internet content, it is easier to write links to pages and data in a relative manner. The previous sections examples can be easily converted to one covering the Internet (Figure 1.3-1). In addition, when writing direct links, to other sites, one would actually be using “absolute” file locations. For example, when linking an HTML page to a search engine: perhaps Yahoo, one needs to use an “absolute” location, or else browsers would be confused. Instead of typing ‘<a href=”yahoo”>Click here to Search</a>,’ one would enter the “absolute” location with regard to the correct Internet protocol3. It would look as follows, ‘<a href=”http://www.yahoo.com”>Click here to Search</a>.’ As can clearly be seen, with the Internet, these things are applicable today!
Figure 1.3‑1
3 There are many different types of Internet protocols. Some of the more famous ones include, HTTP—Hyper Text Transport Protocol, FTP—File Transfer Protocol, TELNET—RFC 804, “Specification for Interoperable Networked Terminals”, as well as a few archaic ones such as GOPHER—Protocol for locating and browsing data, and ARCHIE—Tool for browsing archived data.