Due to advances in sensor technology, sensors are becoming more powerful, cheaper and smaller. This evolution generates big amount of data, which may have no value unless we have the ability of analyzing, interpreting and understanding it. Context-awareness computing (collection, modeling, metamodeling, reasoning and distribution of context) plays a significant role in this challenge. Also, a discussion about the importance and challenges in designing context-aware and event-based applications is presented. An essential aspect that is often neglected in context modeling and also triggers adaptation is the context variability. This document puts the light on this notion that would help the designer in programming adaptation for context-aware systems, by in analyzing, comparing and consolidating works in this sense.