Japanese has only five vowel sounds (a, i, u, e and o), which happen to be the same number of vowels as can be
written with the Roman alphabet. However, many foreign languages, including English, distinguish between more vowel sounds. (Think of
the difference between the first and second [a] sounds in "banana", for instance.) So, many foreign sounds which do not fit into the five
vowels of Japanese have to be covered by one of these five vowel sounds. Thus, "calla" is called kaara in Japanese, and
And "curler" is called kaaraa, hence カーラー. In fact, as demonstrated by "curler" (kaaraa), most English vowel sounds which do not clearly sound to a Japanese person as being i,
u, e or o, tend to fall into the a category.
Try not to think in terms of English spelling (which is quite irregular anyway), but in
terms of the sound, although it always has to be distorted to fit within the structure of the Japanese sound system.
Remember that when using a computer with Japanese language software, the elongation
mark has to be typed in separately, instead of merely repeating the vowel you want to elongate. For example, if you type in ka a ra,
the computer will give you
the latter of which is how the word is written.
Japanese language software accommodates both Hepburn-style and Nihon-style romanizations. So, for example, whether you type in shi
or si, the computer will give you シ,
as mentioned earlier.