Structure is a fundamental and sometimes intangible notion covering the recognition, observation, nature, and stability of patterns and relationships of entities. From a child's verbal description of a snowflake, to the detailed scientific analysis of the properties of magnetic fields, the concept of structure is an essential foundation of nearly every mode of inquiry and discovery in science, philosophy, and art.[1]
A structure defines what a system is made of. It is a configuration of items. It is a collection of inter-related components or services. The structure may be a hierarchy (a cascade of one-to-many relationships) or a network featuring many-to-many relationships.
In biology, structures exist at all levels of organization, ranging hierarchically from the atomic and molecular to the cellular, tissue, organ, organismic, population and ecosystem level. Usually, a higher-level structure is composed of multiple copies of a lower-level structure. (http://en.wikipedia.org/wiki/Structure, Pullan, Wendy (2000). Structure. Cambridge: Cambridge University Press. ISBN 0521782589.