In biology, structures and functions occur across a hierarchy of size,
extending from molecules to organisms.
These hierarchies occur largely as nested sets wherein a given hierarchy
is part of another, but also contains many hierarchies of its own.
The EBS database uses sixteen hierarchical levels to build a
qualitative framework onto which quantitative data can be attached.
Building such an framework starts with a theoretical model that
slowly gives way to the realities of the literature - as more and
more data are added.
- An organ hierarchy.
- A brain and spinal cord hierarchy.
- An operational hierarchy.