# Semantic Web and Knowledge Graphs for Industry 4.0
## 6 Reference Generalized Ontological Model  
The proposed Reference Generalized Ontology Model (RGOM) is a universal platform developed with the composition of the domain specific and core ontologies along with the authors identified concepts based on reference architectural model Industrie 4.0 (RAMI4.0) [7; 8; 61]. Figure 5: High level representation of Reference generalized ontological model. The methodology for the proposed reference generalized ontological model (RGOM) is composed of the following steps. * A detailed survey is conducted by analyzing the recent literature for the ontological models for industry 4.0. In this step, key ontologies regarding the production line, supply chain, etc., were shortlisted based on the search methodology. * Industry 4.0 architecture such as Reference architectural model Industrie 4.0 (RAMI 4.0) was studied to find out the requirements needed for the industry 4.0 production. * A comparative study is then conducted to find out the gap between the standards and the current state of the art models. During this step, it was identified that the current ontologies do not follow the requirements of the RAMI4.0 and are unable to follow the reuse principle of linked open data. * The existing vocabularies were reused with the additional concepts that were missing. The whole process was performed iteratively. Based on the literature review and RAMI4.0, the proposed RGOM considers core areas such as time, location, sensor, and different domains such as product, process, and machine along with the order, supply chain, warehouse, etc., and explores all the concepts and relationships among them. This implies that the RGOM provides a detailed unified model which takes the I4.0 domain knowledge from raw material to finished product including supply to the customer as well as monitoring the different situations of machines and processes. Machines and products are separated from the resource ontology [5], to form a machine ontology and a product ontology to accommodate more concepts and relations. For instance, the product ontology specify the concepts such as product (production of product) and service (maintenance usage) adopted from RAMI4.0 and identified concepts such as sales ontology are coupled. This helps to provide a full view that the order is placed for a service or for the manufacturing of product, depending on the order the either the service or the resources in the manufacturing production line will be reconfigured. RGOM has reused the existing vocabulary, i.e., the machine which is a manufacturing facility and is associated with the workstation by reusing the isPartOf property from Dublin core vocabulary. The process(s) happening at different times and locations is linked to the manufacturing resources by process ontology using performProcess property. It describes the basic taxonomy of all kinds of processes from manufacturing to human process(s) and logistic operations. Sales ontology defines customer orders concepts for the product. The order can have various concepts such as design, quantity, delivery date, etc., Supply chain ontology can assist in monitoring the delivery of the manufactured product to the customer. Thus, the context of the core ontologies alone would not be able to answer why, where and what type of questions, but the RGOM is able to infer all the contextual information ranging from a particular entity situation to the complete production line. The consistency of the RGOM has been evaluated through the reasoner (software tool) known as Hermit ([[http://www.hermit-reasoner.com/](http://www.hermit-reasoner.com/)]([http://www.hermit-reasoner.com/](http://www.hermit-reasoner.com/)), accessed on 1 May 2021).