Concern arises as a formal grouping of autonomous entities, some of which are in spite of their legal personality subordinate to another subject so that the group acts as a centralized entity comprising a single organization and unity of management.
Concern is defined by Commercial Code § 66a, paragraph 7: a group consists of a single business group of at least two persons, one of which is against the other person in controlling position. A concern may arise based on the simple fact of the existence of a controlling and controlled entities (rebuttable presumption) - then we are talking about a de facto concern. The group may be constituted on the basis of the controlling agreement - then we are talking about contracting concern.
Defining element of concern is the merger of several legally autonomous persons to the system allowing common management. Individual group companies are managed in the interests of the whole, which may not lead to the simultaneous benefits of each of the group companies.