## 2 Materials and Methods
### KB System
#### 2.1.2 Knowledge Processing Phase  
The knowledge processing phase begins with the definition and classification of DFW rules associated with given manufacturing technology. This phase aims to create an ontology (i.e., the structuring and formalization of data into hierarchies and classes to establish the relations among the data required for efficient machine processing that is a comprehensive description of the domain of interest (welding design rules) concerning the users' needs. Table 1 presents the overall structure of the repository used for collecting and storing the rule-related information. The structure of the repository is the semantic (logic) used to switch from tacit knowledge (unstructured) to explicit knowledge (structured). The repository stores rules based on the rule number, which is a positive, progressive number. It contains three clusters of information, namely, (i) manufacturing technology, recalling the technological aspects (i.e., manufacturing technology class and manufacturing process type) related to a given rule; (ii) material, providing material information (i.e., material class and material type) of a given rule; and (iii) CAD feature recognition, identifying geometric parameters and thresholds associated to a given rule. In addition to these sections, information about rule type is stored (i.e., info, warning, critical). An example for the W025 DFW rule is reported to clarify some aspects of the information to insert in the given structure. Concerning the first section of the knowledge processing phase, classification of manufacturing technologies requires the definition of different clusters: (i) welding technology class (i.e., welding technology--fusion welding, solid-state welding and brazing, and soldering); (ii) manufacturing technology type-level I (e.g., arc welding, oxyfuel gas welding, resistance welding, and newer welding for the fusion welding technology class); and (iii) manufacturing technology type-level II (e.g., metal inert gas, tungsten inert gas, fluxed core, submerged arc, etc. for the arc welding manufacturing technology type-level I). The overall classification of welding technologies is proposed in Figure 2. It is worth noting that in the current research, only the fusion welding class was considered with the possibility to further extend this study to the other classes (i.e., brazing and soldering, and solid-state welding). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Rule \#** & **Rule Type** & \multicolumn{3}{c}{**Welding Technology**} & \multicolumn{3}{c}{**Material**} & \multicolumn{3}{c}{**CAD Features and Algorithms**} & \multirow{2}{*}{**Source**} \\ \cline{2-2} \cline{6-11}  & **Class** & **Type\(-\)Level I** & **Type\(-\)Level II** & **Class** & **Type** & **CAD Features** & **PMI** & **Parameters** & **Rule** \\ \hline W025 & Warning & Fusion & Fusion & \multirow{2}{*}{Arc welding} & \multirow{2}{*}{N.A.} & \multirow{2}{*}{All materials} & \multirow{2}{*}{N.A.} & - Weld beads & \multirow{2}{*}{N.A.} & \(Z=\) dimension of the weld beads & & \\  & & welding & & & & & - Weld beads & & & \\  & & & &  
The adoption of these clusters is necessary to classify DFW rules that are generic for a technology class (e.g., fusion welding) or specific for a manufacturing operation of the defined technology class (e.g., metal inert gas). Indeed, a DFW rule may be valid for the generic manufacturing technology class (e.g., fusion welding) regardless of the specific process. In this case, the two levels or only the second level related to the welding technology type are not specified (N.A. ; not applicable). Conversely, a welding rule may be valid only for a specific process (e.g., metal inert gas) and cannot be generalized for the welding technology class that contains this process (e.g., fusion welding).