TRIZ employs term "evolution of technical systems" without giving it a formal definition. But without defining evolution of technical systems formally it is impossible to properly formulate any law of such evolution. This paper aims to bridge this gap.
To begin with, any technical system is created by borrowing parts (and sub-systems) from other systems (which can be called donors) with their subsequent combination and modification. Donors do not have to be technical systems. They can be biological or natural. For example, planes were created by borrowing the idea of wings from birds with their subsequent modification. Sometimes entire biological organisms are incorporated into technical system. On the diagram below circles denote systems and arrows denote borrowing:
Systems can be evaluated by proximity to each other. (However discussion and selection of the measure of proximity is beyond the scope of this paper. We just assume that it exists.)
For example, Boeing-747-100(1966), Boeing-747-200(1968), Boeing-747-300(1980), Boeing-747-400(1985), where numbers in parentheses are years when the planes were designed is such a series. Every subsequent modification borrowed more from the previous one than from anything else. Also every subsequent modification was closer to what it borrowed from the previous one than to what it did not borrow. That is why they can be called evolutionary series of the abstract technical system named Boeing-747.
Similarly, ARIZ-59, ARIZ-61, ARIZ-64, ARIZ-68, ARIZ-71, ARIZ-77, ARIZ-85 are evolutionary series of the abstract technical system called ARIZ for the same reasons.
In the above diagram there are instances of both intra-system and inter-system evolutionary transitions. For example, borrowing from the instances of the three upper systems resulted in creation of the instance of a new system (painted brown). This is inter-system evolution. All other types in the diagram are intra-system evolutionary transitions.
Inter-system evolutionary transition can be subdivided into:
In the above diagram just one evolutionary transition is of inter-class type. Inter-superclass transitions can be defined in a similar fashion.