## 3 Identifying Promising Vacant Technologies
### Detailed Procedures
#### 3.2.3 Investigation into Emerging and Vacant Technology Fields Using an ARM-Based Network Analysis  
The final step is designed to deduce the technology development strategy through network analyses: IPC-based network analysis and significant keyword-based network analysis (Figure 4).  
A patent network analysis measures the interactions between technologies while visualizing and analyzing those interactions. Patent data has IPC codes, which are classification systems for patents and significant keywords that express core technologies. A network analysis is performed via the association rule mining (ARM) method using the patent-IPC matrix and patent-keyword matrix, which are co-occurrence matrices derived in the process of preprocessing patent data. In this step, we analyze the relationship between technical fields in relation to the IPC and the relationship with the core technology in relation to keywords. We deduce the overall technology area and detailed technology development strategy through two types of network analyses.  
An ARM is an algorithm that aims to identify dependencies between items in a data set and to represent the various identified rules [67]. ARM defines indicators such as support, confidence, and lift based on the conditional probability that IPC codes in the analysis data will appear. Therefore, we use ARM's indicator to explain the rules and select the appropriate ones. Here, A and B are defined as a set of IPC codes. Support is an indication of the IPC codes' appearance frequency in the database. The support of rule (A \(\rightarrow\) B) can be calculated by the following Equation (1):  
\[\text{Support: (A}\rightarrow\text{B)}=\text{P(A}\cap\text{B)}. \tag{1}\]  
Confidence is an indication of true frequency in if-then rules where B appears when item A appears. The confidence of rule (A \(\rightarrow\) B) can be calculated by the following Equation (2). The confidence is used to analyze the association of B with A. However, confidence is limited in the overall analysis because the confidence value depends on the size of A.  
\[\text{Confidence: (A}\rightarrow\text{B)}=\text{P(B}\mid\text{A)}. \tag{2}\]  
Figure 4: Investigation into emerging and vacant technology fields.  
Lift is an indication of the probability of an item set based on the probability of the individual items in the set. The lift of rule (A \(\rightarrow\) B) can be calculated by the following Equation (3). If the lift is greater than 1, then items A and B are dependent on each other. On the other hand, if the lift is 1 or less, items A and B are interpreted as unrelated [68; 69; 70].  
\[\text{Lift: (A}\rightarrow\text{B)}=\text{P(B}\mid\text{A)}\cdot\text{P(B)}. \tag{3}\]  
In the patent analysis, IPC codes and patent keywords can be applied to ARM to determine the association rules. The association rules (IPC code\({}_{1}\rightarrow\) IPC code\({}_{2}\)) determine that IPC code\({}_{1}\) influences the development of IPC code\({}_{2}\). We build an IPC network through the association rules. The keyword network is expressed based on the co-occurrence matrix. To analyze the relationship between technologies using networks and indicators, we analyze the relationship on a network graph using the significant keywords with various indicators, such as degree centrality, closeness centrality, and betweenness centrality.  
The ARM-based IPC network that visualized the IPC code association rules and the keyword network that visualized technical keywords with a network graph analyze the relationship between IPC codes and keywords. The results of the SNA analysis can be used as guidelines for R&D and for determining technological feasibility.