Input data
Before SymSyn simulations can be performed, input data needs to be prepared. The required structure of input data depends on the purpose of the model. SimSyn provides different data link types to implement variant types of simulations.
A data link is a link of a Vensim model element to a database table column. At the moment subscripting data links (SDL), time-series data links (TSL) as well as time-dependent subscripting links and combinations of SDL and TSL are supported.
SDL enable creating multiple instances of a Vensim model. This may be used for spatial simulations or to run and compare thousands of alternative model parametrizations (e.g. sensitivity analyses, scenario runs etc).
A SDL is used to link a Vensim constant to a database table column and run one independent simulation for every row value in this column. Multiple SDLs may be defined to link more than one constant to every independent simulation run (Fig. 1; A).
Fig. 1. A) Database table with two subscripting data links (SDL); B) Database table with two time series links (TSL)
A time-series data link (TSL) is used to assign database table columns as time series to Vensim variables (Fig. 1; B). Multiple TSLs of a single or of multiple database tables may be assigned to a single VENSIM model.
As an additional functionality, SDLs may optionally be equipped with a simulation timestamp (see also section 6). For instance, a first SDL may be assigned to the initial simulation time 0 of a VENSIM variable element and a second SDL may be assigned to a final time step 100 of the same VENSIM variable. SimSyn linearly interpolates between the first and the second SDL values in the course of its integration.
In some instances combinations of SDL and TSL are required. In cases where SDLs and TSLs are assigned to a VENSM model, the time series are duplicated and assigned to every single run of the SDL. SDLs and TSLs may refer to the same or different database tables. For this type of data-linked simulation, larger computational overhead is to be expected (see also section 10).