Abstract Question answering systems retrieve information from documents in response to queries. Most of the questions arewho-andwhat-type questions that deal with named entities. A less common and more challenging question to deal with is thewhy-question. In this paper, we introduceLemaza(Arabic forwhy), a system for automatically answeringwhy-questions for Arabic texts. The system is composed of four main components that make use of the Rhetorical Structure Theory. To evaluateLemaza, we prepared a set ofwhy-question–answer pairs whose answer can be found in a corpus that we compiled out of Open Source Arabic Corpora.Lemazaperformed best when the stop-words were not removed. The performance measure was 72.7%, 79.2% and 78.7% for recall, precision andc@1, respectively.

A Question Answering (QA) system is concerned with building a system that automatically answer questions posed by humans in a natural language. Compared to other languages, little effort was directed towards QA systems for Arabic. Due to the difficulty of handling why -questions, most Arabic QA systems tend to ignore it. In this article, we specifically address the why -question for Arabic using two different approaches and compare their performance and the quality of their answer. The first is the baseline approach, a generic method that is used to answer all types of questions, including factoid; and for the second approach, we use Rhetorical Structure Theory (RST). We evaluate both schemes using a corpus of 700 textual documents in different genres collected from Open Source Arabic Corpora (OSAC), and a set of 100 question-answer pairs. Overall, the performance measures of recall, precision, and c@1 was 68% (all three measures) for the baseline approach, and 71%, 78%, and 77.4%, respectively, for the RST-based approach. The recently introduced extension of the accuracy, the c@1 measure, rewards unanswered questions over those wrongly answered.