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The models developed in IPSIM framework have been made using the DEX method and implemented with the DEXi software (Bohanec, 2003). DEX is a method for qualitative hierarchical multi-attribute decision modelling and support based on a breakdown of a complex decision problem into smaller and less complex sub-problems.
This tool, in general used to construct decision models has been used here in an original way to develop simulation models. In our case, this method allowed us to evaluate an injury profile (IP) (output of the model) depending on the combination of 3 major attributes, cropping practices, weather and soil and field environment. Then, each of these 3 attributes has been broken down into different sub-attributes, themselves broken down into basic attributes (inputs of the model) described at a lower level (tree structure that represents the skeleton of the model).
In the DEX method, the aggregation of values up the tree is defined by ‘‘utility functions’’ based on a set of ‘‘if-then’’ aggregation rules. The aggregation functions are presented in the form of tables and basic attributes are entered in a qualitative manner (nominal or ordinal variables) or quantitative (variables intervals).
The selected variables, the values of class, and aggregation functions have been identified and characterised through the bibliography and the expertise. Only the factors easily informed and with major consequences on the pests have been retained.
The option chosen has therefore been a process of qualitative hierarchical and aggregative modelling. This  choice is therefore focused on an approach that can incorporate a high level of complexity. In addition, this choice allows to reach an essential level of reusability and the simplicity of the tool allows an easy appropriation by the actors in the research or development.

The construction of the model is realized in 3 steps (thanks to the DEXi software and by bibliography and expertise):
- identification and organisation of the attributes
- Definition of attributes scales
- Definition of aggregation functions (aggregation functions of type "if…then")

DEXi software can be downloaded freely and free of charge on the website:

http://kt.ijs.si/MarkoBohanec/dexi.html

A manual for use in English of this version is available at the following address:

http://kt.ijs.si/MarkoBohanec/DEXi/html/DEXiDoc.htm