# A Roadmap to Integrate Digital Twins for Small and Medium-Sized Enterprises
## 4 Discussion
### RQ1: Design of the Communication Framework
A MySQL database was chosen to fit the low-cost structured database need. As with other database solutions in the market, MySQL comes with the essential user authentication functionality. For SMEs, there is a large choice of data storage options. The decision begins with an understanding of what type of data are being extracted. For data that largely consist of numbers and values, the structured database holds greater value. This is especially true for situations where the SMEs may have limited storage space and data processing power. In other cases when the data are of a qualitative nature, such as images, text or generally does not fit into a defined model, the unstructured database will be suitable. In either case the SME must then decide how their data will be processed and utilised in decision making processes. In the case of structured databases, as in the use case of this article, SMEs will be able find many readily available resources (e.g., MySQL and Grafana) to store and visualise their data. For unstructured data, SMEs can hardly find a 'one-size-fits-all' solution but rather require fine-tuning of available solutions which are mainly driven by the costs and the nature of the data. SMEs have many options for low-cost databases, both on-site and on the cloud. If the SME is looking for multi-client access, the cloud-based solution may be more appropriate. The implementation of databases, though not overly complicated, may require skills in package installation, knowledge in basic programming syntax and conversions among data types, which has been demonstrated in (Section 3.2). For our experiment, Node-Red was used as a software to wire together the various individual components, namely the field equipment PLC, the MySQL database and the 3 DExperience modelling software. Node-Red is built on the Node.js where it has the added benefit of being an I/O model that is lightweight and efficient enough to run on cost-efficient hardware such as Raspberry Pi. Node-Red is also a user-friendly software that combines its visually intuitive design with drag-and-drop blocks and connections, as well as its ability to express code in a visualised manner as opposed to textual code. Besides, Nodered has the added advantage of being multi-client accessible, lightweight, robust and easy to access via the cloud for developers in I4.0, DT, IoT connectivity and smart devices. It also has vast programming capabilities with its large node library, including built-in support for popular IoT protocols (e.g., Modbus, OPC UA and MQTT), giving it the ability to wire together field devices and automation controllers to cloud services and databases. For situations where nodes for a specific purpose are not available, there is customisability with function blocks using JavaScript. This was demonstrated in our experiment when storing data in the specified data tables. Our communication framework also allowed the end-to-end implementation of DTH, which allows the digitization and traceability of the flow of information up- and downstream throughout the entire PLM processes. Our experiment scenario demonstrated DTH could be readily integrated into typical manufacturing scenarios, such as machining tools, where users could view a comprehensive history log through the database and keep track of the manufactured items along their life cycles. We acknowledged that the experiment in this study has its limitation in fully demonstrating the capability of DTH; however, it does not limit the DTH from expanding its coverage that encompasses the entire PLM from design to disposal, integrating different stakeholders along the supply chain, enhancing collaboration, decision making and data management. SMEs that aim to extract greater value along the entirety of the product lifecycle, as noted in Sections 1 and 2, may consider supply chain integration into the DT and DTH and utilising cloud-based solutions with multi-client access.