# A Named Entity and Relationship Extraction Method from Trouble-Shooting Documents in Korean
## 6 Rule-Based Approach for Knowledge Extraction  
### Relation Sets and Rules to Find the Relations  
Maintenance documents have multiple sentences that express maintenance knowledge, which can be expressed with simplified phrases if key entities are extracted from the sentences. Table 2 shows the simplified formats of maintenance knowledge, which consists of key entities such as \"PART\", \"FAILURE\", and \"ACTION\". The simplified formats are sets of relations between entities, so they are called \"relation sets\" in this paper. The \"PARTFAILURE\" and \"FAILURE-PART\" relation sets are simplified phrases of the sentences in the failure mode section of maintenance documents. The \"PART-FAILURE\", \"FAILURE-ACTION\", and \"FAILURE-PART-ACTION\" relation sets are simplified phrases of the sentences in the repair action section of maintenance documents. The key entities of relation sets could be found by applying NER methods. The relation between entities should be inferred from the syntactical structure of a sentence, which could be provided by the results of dependency parsing. Rules using the syntactical structure can be pre-defined to find the relations between entities. Five rules were defined for the five relation sets. Rules are explained with variables and functions. \"_words\({}_{i}\)_\" is a variable for a set of words that are recognized as \"PART\", \"FAILURE\", or \"ACTION\". \"\(DP\)\" is a mapping function of two words for their dependency relationship notations. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Notation** & **Dependency Relationship** & **Notation** & **Dependency Relationship** \\ \hline L & Left sign & AP\_OBJ & Adverbial\_Object \\ \hline R & Right sign & AP\_MOD & Adverbial phrase\_Modifier \\ \hline NP\_SBJ & Nominal\_Subject & AP\_CMP & Adverbial phrase\_Complement \\ \hline NP\_OBJ & Nominal\_Object & VNP\_SBJ & Positive copula\_Subject \\ \hline NP\_MOD & Nominal\_Modifier & VNP\_OBJ & Positive copula\_Object \\ \hline NP\_AJT & Nominal\_Adverb & VNP\_MOD & Positive copula\_Modifier \\ \hline NP\_CMP & Nominal\_Complement & VNP\_AJT & Positive copula\_Adverb \\ \hline NP\_CNJ & Nominal\_Conjunctive & VNP\_CMP & Positive copula\_Complement \\ \hline VP\_SBJ & Predicate\_Subject & VNP\_CNJ & Positive copula\_Conjunctive \\ \hline VP\_OBJ & Predicate\_Object & DP\_SBJ & Determiner phrase\_Subject \\ \hline VP\_MOD & Predicate\_Modifier & DP\_OBJ & Determiner phrase\_Object \\ \hline VP\_AJT & Predicate\_Adverb & DP\_MOD & Determiner phrase\_Modifier \\ \hline VP\_CMP & Predicate\_Complement & DP\_AJT & Determiner phrase\_Adverb \\ \hline VP\_CNJ & Predicate\_Conjunctive & DP\_CMP & Determiner phrase\_Complement \\ \hline AP\_SBJ & Adverbial phrase\_Subject & DP\_CNJ & Determiner phrase\_Conjunctive \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Korean dependency relation tag set. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**ID** & **Relation Set** & **Description** & **Content Type** \\ \hline
1 & PART-FAILURE & Part has a failure & \\ \hline
2 & FAILURE-PART & A failed part & Failure Mode \\ \hline
3 & PART-ACTION & Repair a part & \\ \hline
4 & FAILURE-ACTION & Fix a failure & Repair Action \\ \hline
5 & FAILURE-PART-ACTION & Repair a failed part & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Pre-defined relation sets describing failure modes and repair action. * Rule #1: Given that \(words_{a}\in\) PART, \(words_{b}\in\) FAILURE in a sentence, IF \(DP(words_{a},words_{b})\) = 'NP_MOD' or 'NP_SBJ' or 'NP_AJT', THEN \((words_{a},words_{b})\in\) PART-FAILURE Rule #1 is for recognizing the relations of the failure mode data, such as \"PART \(\triangleleft\)[JKG] FAILURE\", PART \(\circ\)/ \(\gamma\)[JKS] FAILURE\", or \"PART \(\circ\)[JKB] FAILURE\", as being part of the PART-FAILURE set regardless of differences in their forms.