Table 3.

Group properties and criteria.

Property	Group criteria
Literature content type [45,46]	•Application: detailed descriptions of the application in specific fields, with technical details and detailed case studies. •Framework: general descriptions of the application in respective fields, with in-depth analysis, implementation framework, and a rather detailed case study. •Discussion: research summary or discussion on selected literature concerning a particular topic. •Review: structured research summary on existing literature concerning a particular topic.
Publications' objective theme group	•Concern: related to digital twins in general, not focused on places and/or humans. •Hospital: digital twins with the purpose of places. •Patient: digital twin with the purpose of humans.
Publications' objective subtheme group	•Aspects, issues and/or policies: regard to aspects, issues, problems, risks, requirements and/or policies of digital twin, like security, privacy, or knowledge management. •Care: digital twin of services or supplies related to the health of a patient, like crisis/emergency alarms, notifications, and management. •Device: about a device or an equipment digital twin, like dual energy x-ray absorptiometry or electrocardiogram. •Facilities management: digital twin that integrate multiple disciplines to ensure the organization has the necessary resources to function on a day-to-day operation [47]. •Precision medicine: digital twin customized individualized patient's care and treatment based on genetic, environmental and lifestyle factors [48]. •General: related to digital twins in general, not focused on a specific subtheme.