Vega Application (Virtual Models for evaluating the properties of chemicals within a global architecture) is a platform developed on the basis of contributions from the EU projects CAESAR, ORCHESTRA and ANTARES.

Vega includes QSAR models and rule-based expert systems for the prediction of human toxicity endpoints (mutagenicity, carcinogenicity, developmental toxicity and skin sensitization), eco-toxicological endpoints (acute aquatic toxicity on Daphnia and fish), environmental properties (BCF and ready biodegradability) and physico-chemical properties (LogKow).

The applicability domain of predictions is assessed using an Applicability Domain Index (ADI) that has values from 0 (worst case) to 1 (best case).

The ADI is calculated by grouping several other indices, each one taking into account a particular issue of the applicability domain. Most of the indices are based on the calculation of the most similar compounds found in the training and test set of the model, calculated by a similarity index that consider molecule's fingerprint and structural aspects (count of atoms, rings and relevant fragments).

For each index, including the final ADI, three intervals for its values are defined, such that the first interval corresponds to a positive evaluation, the second one corresponds to a suspicious evaluation and the last one corresponds to a negative evaluation.