  Philosophical questions arise about the senses in which these various organisms serve as “models.” Potentially, models may embody a range of characteristics: as typical or representative; as ideal or perfect; as convenient, tractable, or manipulable; as homologous (conserved evolutionarily); as analogous; as exemplars; as abstractions. Models may also be used in a variety of ways: to model disease processes; to model normal processes; as structural models; as type organisms representative of the species or higher phylogenetic level; as heuristic tools; as mathematical  devices.[35] In a recent article examining researchers’ use of the flowering plant Arabidopsis thaliana as a model organism, Sabina Leonelli (2008) points out that models can be abstract (vs. concrete) in different ways: absolutely, in terms of their sense perceptibility; or relatively, in terms of their physical meaning with respect to the phenomena represented or the range of phenomena they are taken to represent. She then shifts the philosophical focus from models themselves to modeling practices: abstraction, for example, becomes a component of the activity of producing a model rather than solely an attribute of the model. This approach emphasizes the need to attend not just to the relationship between model and phenomenon modeled but the material, social, and institutional settings and varied commitments of researchers. 