As a consequence, a first level differentiation of basic types of material entity should exhaustively cover all possible combinations of these two primary building blocks.
This results in five basic types of material entity (i.e. 'object', 'fiat object part', 'object aggregate'fiatiat object part aggregate'objectect with fiat object part aggregate'; Fig. 3, 7).
Considering the foundational role that BFO claims to take for the scientific domain, an important question is whether its distinction of three basic types of material entity (i.e. fiat object part, object, object aggregate) is (i) exhaustive and (ii) sufficiently differentiated and specific.
There are two basic types of suture materials; absorbable ones such as catgut (which comes from sheep intestine) or synthetic substitutes; and nonabsorbable materials, such as nylon sutures, steel staples, or adhesive tissue tape.
All possible combinations of these five building blocks result in 31 (i.e. five different types of group-building blocks, each of which can be absent or present in the group, results in 52 possible combinations minus the combination of the absence of all building blocks: 52−1 = 31) basic types of groups of material entity (some of which are depicted in Fig. 6).
The distinction between groups and clusters requires to further differentiate the three basic types of aggregate of material entities discussed so far, i.e. object aggregate, fiat object part aggregate, and object with fiat object part aggregate, into respective types of clusters and groups (table 2; Fig. 6).
In order to receive an exhaustive list of theoretically possible basic types of constitutively organized material entities one thus only has to permute all possible combinations of bona fide objects and fiat object parts and their distribution in space.
