Systems describe where materials are located (stocks) and where they are moving (flows), without quantities.
The knowledge about systems of the physical economy is often highly fragmented, particularly for minor metals, critical raw materials and for end of life management.
Data about the physical economy tend to be highly fragmented or lacking entirely. The reference points of data collected are often unclear (described in words only), which results in ambiguous meaning and misinterpretation of the data.
Models are mathematical representations of material cycles and their drivers. They are used to forecast resource demand and supply and to test strategies under different conditions. The robustness of models is usually limited by a lack of robust data and system understanding.
A model can never perfectly represent a natural system.
Uncertainties in MFAs are caused by data paucity and errors in system definitions.
Ignoring uncertainty can result in wrong interpretations of the results.
Indicators are used to measure the performance of a system or to capture the essence of a system with numbers.
Indicators are often poorly defined.
Strategies to enhance the indicator performance often cause problem shifts.
Visualisations are used to capture the essence of complex systems using images, and to communicate the results in an effective way.
The systems analysed tend to include several dimensions, which are difficult to communicate in words.
Resource management strategies tend to be ineffective and shift problems if they are not based on a robust system understanding.
Strategies for monitoring individual aspects of the physical economy tend to be expensive and of limited use for resource strategies if they are not based on an explicit system definition.