Astronomy enters the period of Big Data and Data-Driven Discovery. Data bases increase every days with terabytes of new observations, and the catalogs start to contain milions of objects. Thus the most important thing is to see certain order in these enormous data stream, and next we should gain - from this order - a real, deeper understanding of what we see. We face the same problem in quasar research. Catalogs contain 200 000 well studies quasars, over 1 000 000 of quasars are identified, and the numbers are growing.

Different quasars have of course different luminosities, which is easy to understand since they differ with respect to the mass of the central black hole and the distance from us. However, stars differ between themselves not only with respect to the brightness and the distance, but they have different colors. And then the discovery came that stars form a stream on the color-color diagram which was later named stellar main sequence. Finally, it was explained that the location of a star on the stellar main sequence is determined by the temperature of the stellar atmosphere.

Quasars also have their colors, and the corresponding classification also showed a pattern, named now Quasar Main Sequence although this sequence is not as narrow as the stellar main sequence. Quasars are much more complex than stars due to the lack of spherical symmetry - material flowing onto the black hole forms an accretion disk around the central black hole, and this disk is hotter closer to the black hole and cooler further out. Therefore, it is difficult to establish what is responsible for the observed trend. The first ideas for a key parameter were the inclination of the symmetry axis with respect to the observer, and the ratio of the mass flowing toward the black hole to the black hole mass. We have our own idea and we think that the answer is actually quite similar as in the case of stars. The aim of the project is to prove this hypothesis. We will do it through two different actions. We will calculate theoretically the quasar models for a broad range of paramete! rs. We will also collect available observations for numerous quasars with the aim to check whether the parameter which, we think, is the key parameter, actually well describes the observed Quasar Main Sequence.