We describe a lexicon of Arabic verbs constructed on the basis of Semitic patterns and used in a resource-based method of morphological annotation of written Arabic text. The annotated output is a graph of morphemes with accurate linguistic information. An enhanced FST implementation for Semitic languages was created. This system is adapted also for generating inflected forms. The language resources can be easily updated. The lexicon is constituted of 15 400 verbal entries. We propose an inflectional taxonomy that increases the lexicon readability and maintainability for Arabic speakers and lingui sts. Traditional grammar defines inflectional verbal classes by using verbal pattern-classes and root-classes, related to the nature of each of the triliteral root-consonants. Verbal pattern-classes are clearly defined but root-classes are complex. In our taxonomy, traditional pattern-classes are reused and root-classes are simply redefined. Our taxonomy provides a straightforward encoding scheme for inflectional variations and orthographic adjustments due to assimilation and agglutination. We have tested and evaluated our resource against 10 000 diacriticized verb occurrences in the Nemlar corpus and compared it to Buckwalter resources. The lexical coverage is 99.9 % and a laptop needs two minutes in order to generate and compress the inflected lexicon of 2.5 million forms into 4 Megabytes.