Combining Indexing Units for Arabic Information Retrieval

1.1. Motivation

Let consider the Arabic root “kassama-قسم” and some related words (cf. Table 1). In one side, root-based methods will relate many derived words to the same form and this will cause ambiguity and reduce precision. If we consider the example, “inkassama-انقسم” (was divided) and “akssama-اقسم” (swear) will be represented by the same index i.e. “kassama-قسم” (divide).

Stem indexes reduce ambiguity (Ayed, 2014; Bounhas et al., 2015), but it will from the other side, reduce recall, since some studies (Al-Kabi et al., 2011) showed that in most cases, morphological variants of words have somehow similar semantic interpretations and are not completely dissimilar and different word forms may bear similar meaning. When we apply a light stemming to the same example, “alinkissamat-الانقسامات” (the divisions) and “inkissam-انقسام” (division) will have the same stem but their semantic relation with “kisma -قسمة” (division) will be ignored.

Indeed, light stemming methods offer less recall and more precision. However, lemmatization helps to achieve better recall rates, but reduces precision. Thus, combining these techniques seems promising as it realizes some compromise between precision and recall, in a way we ensure that “alinkissamat -الانقسامات” (the divisions) is equal to “inkissam-انقسام” (division), not so far from “inkassama-انقسم” (was divided), a little bit different from “iktassama-اقتسم” (share somebody in something), but not totally different from “kaassama-قاسم” (share something with somebody) and that “akssama-اقسم” (swear) and “istakssama-استقسم”(conjure) are somehow related (cf. Figure 1).