Arabic orthography is a cursive system, running from right to left. Only consonants and long vowels are written. There is no upper and lower case distinction, nor can the isolated forms of letters normally be juxtaposed to form words.
The Art of Arabic Calligraphy
Arabic belongs to the group of Semitic alphabetical scripts in which mainly the consonants are represented in writing, while the markings of vowels (using diacritics) is optional.