Systems are sets of entities, physical or abstract, comprising a whole where each component interacts with or is related to at least one other component and they all serve a common objective. The scientific research field which is engaged in the interdisciplinary study of universal system-based properties of the world is general system theory, systems science and recently systemics. This field investigates the abstract properties of matter and mind, and their organization, searching for concepts and principles which are independent of the specific domain, substance, and type of system, and of the spatial and/or temporal scales of its existence.
Systems science can be viewed as ... "a metalanguage of concepts and models for interdisciplinary use, still now evolving and far from being stabilized. This is the result of a slow process of accretion through inclusion and interconnection of many notions, which came and are still coming from very different disciplines. The process started more than a century ago, but has gathered momentum since 1948 through the pioneering work of Norbert Wiener, John von Neumann, Ludwig von Bertalanffy, Heinz von Foerster and W. Ross Ashby, among many others" (Charles François, 1999).
Systems ecology focuses on interactions and transactions within and between biological and ecological systems, and is especially concerned with the way the functioning of ecosystems can be influenced by human interventions. It uses and extends concepts from thermodynamics and develops other macroscopic descriptions of complex systems.
The Work Breakdown Structure (WBS) is a means of organizing system development activities based on system and product decompositions. The systems engineering process produces system and product descriptions. These product architectures, together with associated services (e.g., program management, systems engineering, etc.) are organized and depicted in a hierarchical tree-like structure that is the WBS.