  In this paper, categorization of nanomaterials is examined from four
perspectives; context, criteria for success, ensuring measurements are
relevant, and the life cycle of a nanomaterial. For each perspective, its
relevance to categorization is discussed as well as the difficulties it
presents. For example, while the context of assessing potential harm to living
things and the environment is clearly important, other contexts are often
needed and require different categorization schemes. Understanding what success
means for a categorization scheme, within its target context, is critical to
making sure a categorization is actually useful. The complexity of
nanomaterials and their interactions makes generating and collecting the
required data and metadata to support categorization a challenge. Finally, the
transformation a nanomaterial undergoes through its lifetime, including the
testing process, present additional challenges to accurate categorization. How
these factors impact development of usable categorization schemes is analyzed.
