The objective of this rather complicated looking diagram is to give an impression for the technically minded reader as to how the computer model is structured and also to provide a glimpse of its real complexity. The reader not interested in the model per se can safely skip this brief without losing the continuity of the report.
The model has 10 regions (Figure A) each represented on six different strata (Figure B). The interdependence of all regional models is expressed through appropriate interconnections and exchange mechanisms. For some strata several representations with different degrees of resolution, i.e., different amounts of detail, are used. For instance, on the economic stratum (Figure C) there is a regional macro economic model given in terms of gross regional product, GRP, and major expenditure components: consumption, investment, government expenditure, etc., and also a micro economic model which specifies the economic output and expenditure components in terms of nine production sectors.
An illustration of how different strata are integrated into an overall world system model is shown in Figure D which presents the interconnections between three submodels — population, economics and agricultural production — for the purpose of food supply analysis. Each of these submodels is quite complicated in itself and only some components and variables of key importance for the interconnections are shown in the figure.
The individuals stratum model determines deficiency in diet for individuals (DD) on the basis of population level (POP), the food diet needs (FDN), and food available given in terms of dietary components; protein (PT), animal protein (PTA), calories (CAL) and fats (FT).
The population model determines the population (POP) in various age groups and labor available for agriculture (LA) and non-agriculture (LNA). The population change is influenced by diet deficiency.
For the sake of simplicity only a portion of the economic model dealing with the production functions is shown in the figure and in terms of only two sectors: agriculture and non-agriculture. The production function for the non-agricultural sector is given in purely economic terms, as the so-called Cobb-Douglas type function, with the non-agricultural labor and capital as the inputs (LNA and KNA) and the level of production of the sector (YNA), as the output respectively.
The production function for the agricultural sector, however, is represented in physical terms on the technological stratum because of interest in the assessment of alternative technologies of food production. It has two basic parts: food production and land development. The main inputs come from the rest of the economic model, namely, investment in land development (LI), investment in agricultural production (IAP), allocation of economic output for technical inputs to agriculture — fertilizer, seeds, etc. — (YAP), available capital (KA) and labor (LA). There are two basic outputs: arable land available (LD), and the food produced expressed in terms of grain (GR), non-grain (NG), livestock (LV) and fish (FS). The level of food import (FM) is determined by the economic output allocated for food import (MAF), food available for world trade (WFT) and world food prices (WFP). The total available food in the region is then analyzed in terms of basic diet components and fed back to the individual stratum model. Finally, the economic value of the regional agricultural output (YA) is obtained from the physical quantities produced and the pricing mechanisms. The sum of outputs of all production sectors gives the total economic output, i.e., the gross regional product. (Y).
To appreciate the complexity of the model it should be noted not only that each of the boxes In the diagram, e.g., „population model,“ is in itself a complicated model but also that an analogous structure is given for all regions and that other models, such as energy, are also interrelated in a similar fashion.