This is an era which the ELT telescopes define 'the new science' for astronomy. Thus, to make optimal contribution (i.e. valuable scientific output in an efficient, sustainable manner), a mid class telescope such as DAG 4m, must have a carefully designed Systems Architecture, which, in our opinion, could only be possible by means of a proper Systems Engineering (SE) process. From a Platonic perspective, the SE work must be started well before (at least conceptually), even the 'idea' of erecting an observatory. As can be seen from the experiences, this, however, never happens, and also it did not happen in our case. Regarding the facts given above, a SE process for DAG observatory has been initiated soon. As a bunch of constraints had already been formed, the work primarily focuses on the scientific instrumentation. This paper demonstrates various phases of the SE process carried until now. We will also discuss the methodologies/techniques that are planned to be used in the future.