This question's explanation and your answers so far.
あるWebサーバにおいて, 五つのディレクトリが図のような階層構造になっている。このとき, ディレクトリBに格納されているHTML文書からディレクトリEに格納されているファイルimg.jpgを指定するものはどれか。ここで, ディレクトリ及びファイルの指定は, 次の方法によるものとする。
A
┌┴┐
B D
│ │
C E〔ディレクトリ及びファイルの指定方法〕 (1) ファイルは, “ディレクトリ名/…/ディレクトリ名/ファイル名” のように, 経路上のディレクトリを順に “/” で区切って並べた後に “/” とファイル名を指定する。 (2) カレントディレクトリは “.” で表す。 (3) 1階層上のディレクトリは “..” で表す。 (4) 始まりが “/” のときは, 左端にルートディレクトリが省略されているものとする。 (5) 始まりが “/”, “.”, “..” のいずれでもないときは, 左端にカレントディレクトリ配下であることを示す “./” が省略されているものとする。
In “../A/D/E/img.jpg”, the leading “..” moves from the current directory B up one level to A, and then it tries to enter a directory named A. However, only B and D are directly under A; there is no A inside A. This is the mistake of overlooking that “..” already points to A, and writing the name A a second time.
正解 The correct answer is イ, “../D/E/img.jpg”. First check the hierarchy in the figure: A is at the top, B and D sit directly under it, C is directly under B, and E is directly under D. The HTML document is placed in directory B, so the current directory (where you are now) is B. The route from here to img.jpg inside E is B → A → D → E. By specification method (3), the directory one level up is written as “..”, so the step from B up to its parent A becomes “..”. Next you enter D, which is directly under A, giving “/D”; then you enter E, which is directly under D, giving “/E”; finally you append the file name “/img.jpg”. Joining these gives “../D/E/img.jpg”, so イ is correct. The key points are that A, the directory you moved up to, is already expressed by “..” and so its name need not be written again in the path, and that D does not exist inside B, so the “..” that goes up one level cannot be omitted.
In “./A/D/E/img.jpg”, by specification method (2) the leading “.” refers to the current directory, that is B, so it assumes that A is directly under B. However, only C is directly under B; A is the parent of B, not its child. To go to the parent you must use “..”, not “.”.
In “./D/E/img.jpg” as well, the leading “.” refers to the current directory B, so it assumes that D is directly under B. In the figure, however, D is at the same level as B (both are children of A), that is, a sibling directory, so you cannot enter D directly from B. You can reach D only after first going up to the parent A with “..”.