Such models can be represented in many different ways (see also Giere 2004). They are evaluated in terms of their ability to predict the features of the phenomenon and in terms of the mapping between items in the model and the entities, activities, and organizational features in the mechanism (Glennan 2005: 17; Kaplan and Craver 2011). Glennan emphasizes that there is no hard line between complete and incomplete models; rather models are continually in the process of articulation and refinement. Whether a model is complete enough is determined by pragmatic considerations.