## 3 Bill of Assembly (BOA)
### The Proposed BOA  
The proposed BOA is depicted in Figure 2 and is composed of the following information:  
* The BOM--includes information regarding the assembly structure;
* Part parameters (from engineering BOM)--includes information regarding the sizes and features that characterize each of the parts in the BOM;
* Assembly activities (from the PBOM), their times and precedence relations--related to the BOM;
* Manufacturing activities (from the MBOM), the machines, tools, and manufacturing processes, and their parameters. In Figure 2, the final assembly is composed of three sub-assemblies (S.A. 1, S.A. 2, S.A. 3), and sub-assembly 1 is composed of two sub-assemblies (S.A. 1.1, S.A. 1.2) and their raw materials (RM1, \(\ldots\) RM4). The shaded part (in grey) of S.A. 1.1 denotes the completed assembly activities related to S.A. 1.1. Sub-assembly 1.1 (S.A. 1.1.) is further described using an activity precedence diagram in an exploded view, at the bottom of Figure 1. The completed activities are shaded in grey. The processing of each sub-assembly requires the automatic verification of the identity of all its parts using smart contracts. At the lower level of parts and raw materials, a smart tag (hardware chip) has to be scanned for identity verification. At higher levels, the smart contracts of the lower level communicate the completion of their sub-assemblies to the smart contract related to the higher level. This hand-off process requires cryptographic verification of the smart-contract identity between levels. As can be seen in Figure 2, the BOM is the basis for the proposed BOA of each product (workpiece) and the backbone for the additional information. The novelty of the proposed additions to the BOM is encapsulated in an extended activity diagram associated with each sub-assembly in the BOM, detailing all its processes and parameters (example is depicted in Figure 1 for S.A. 1.1). Assembly lines are characterized by an evolutionary assembly of their final product as the main workpiece flows through the workstations. We define the workpiece (WP) to be the main product in the process, meaning that it is the main product part in its evolution. While regular activity diagrams have precedence constraints between nodes and activity times, the proposed diagrams have additional information on: (1) the processed material or sub-assembly, (2) the machine or tool used at each activity, (3) activity static information, and (4) activity dynamic information (workpiece related). These are very important additions of information to the regular precedence diagrams. Our proposed scheme includes the smart-contract verification of the compliance of dynamic data to the static data. We use Figure 1 for illustrating the verification. In Figure 1, the static data specify that the activation of task 6 is dependent on the completion of tasks 4 and 5. The suggested role of the smart contract is to verify these completions by monitoring them, before allowing activity 6 to begin. Activity 6 generates the various measures. These measures are compared against the static data ranges of each parameter. Thus, the verifications related to Figure 1 are as follows:  
Figure 2: Bill of Assembly (BOA) Example: Exploded view. 1. **Depth**: dynamic measure = (5.1), static range = depth (4.5-5.5), Verification result: Compliance;
2. **Diameter**: dynamic measure = (3.95), static range = diameter (3.6-4.4), Verification result: Compliance;
3. **Length**: dynamic measure = (19.90), static range = length (19.8-20.2), Verification result: Compliance;
4. **Width**: dynamic measure = (10.01), static range = width (9.85-10.15), Verification result: Compliance. Two important parameters for each activity are the standard time estimation (static data for an activity) and actual activity time measure (dynamic data).