Pyramidal model on civil information system. - Hristo Toudjarov; Stefan Kalchev; Galya Nenova (CompSysTech, 2000)

Municipal information system. - Hristo Toudjarov; Stefan Kalchev; Galya Nenova (CompSysTech, 2000)

Educational process model. - Hristo Tujarov; Svetlana Avramova; Stefan Kalchev; Milena Stefanova (CompSysTech, 2008)

Data PER model. - Hristo Tujarov; Stefan Kalchev; Vassil Milev (CompSysTech, 2013)