## 2 Materials and Methods
### FHIR Application for the Composite Sensor Kit  
Physiological parameters such as heart rate, oxygen saturation, and pulse rate can be modelled according to HL7 FHIR specifications as observations, and the events of trauma could be modelled as 'assessment scales'. The assessment scales, scoring systems, or indexes are observations with specific characteristics [54]. They have severity-points calculations that can make a quantitative statement on the severity and prognosis of a disease or injury. The scores in FHIR context are used to convert'soft' observations into 'hard' data and evidence. Typically, assessment scales combine the individual values into a total score, which can be calculated for a reference population. The assessment scale can either be a single value, it can consist of several dozen values, which can be calculated using a complex mathematical calculation or a statistical technique. According to the SNOMED-CT classification, TRISS is an assessment scale with SCTID: 273886002; and RTS has a SCTID: 273885003. [55]. The entire context of the patient, observations of physiological parameters, and assessment scales can be encapsulated as a resource bundle and can be uploaded to the FHIR sandbox server using RESTful Web-services, as shown in Table 2.  
In order to demonstrate the real-time integration and interoperability of the sensor kit and EHR, a FHIR sandbox was developed, which hosted the EHR functionality and the trauma episodes were modelled as FHIR resources of 'bundles', 'observations' and 'assessment scales'. The readings from the sensor kit were encapsulated as observations, and trauma scores were encapsulated as 'assessment scales' according to FHIR specifications. SMART on FHIR [14] is a well-known interoperability project with the distinctive goal of developing a platform to enable interoperability between the healthcare application and the FHIR servers, as shown in Figure 3 The project was called Substitutable Medical Applications and Reusable Technologies (SMART), and it adopted web standards application programming interface transport, authentication/authorization, user interface, and standard medically coded data. The system helped specify a clinical description of an ailment in a patient. SMART FHIR provides an interoperable interface to develop web services to integrate end user application with the FHIR servers. \begin{table}
\begin{tabular}{l} \hline // Create a FHIR Observation object. \\ Observation observ= new Observation (); \\ // Assign a randomly generated Universal ID (UUID). \\ observ.setId(uuid) \\ // Set the Observation code according to a Coding System \\ // Coding System refers to RTS trauma score in SNOMED CT \\ observ.getCode() \\.addCoding() \\.setSystem(”[[http://snomed.info/sct](http://snomed.info/sct)]([http://snomed.info/sct](http://snomed.info/sct))”) \\.setCode(”273885003”) \\.setDisplay(”RTS Trauma Assessment”) \\ observ.setValue \\ new QuantityDt() \\.setValue(3) \\ // Set the Date and Time stamp for the observation \\ observ.setIssued( \\ new InstantDt(“2017-05-05T15:30:10+01:00”)) \\ \hline // The Observation upload request above generated the following \\ // response in XML or JSON format after observation is logged to \\ // FHIR Servers. \\ \textless{}Bundle xmlns=“[[http://hl7.org/fhir](http://hl7.org/fhir)]([http://hl7.org/fhir](http://hl7.org/fhir))”\textgreater{} \\ \textless{}id value=“ddde128-e4e2-481 ee-9 acb3-c5 eebc2 ec5e0”/\textgreater{} \\ \textless{}type value=“transaction-response”/\textgreater{} \\ \textless{}entry\textgreater{} \\ \textless{}response\textgreater{} \\ \textless{}status value=“201 Created”/\textgreater{} \\ \textless{}location value=“Observation/96728/\textgreater{}history/1”/\textgreater{} \\ \textless{}etag value=“1”/\textgreater{} \\ \textless{}lastModified value=“2017-05-05T15:30:10+01:00”/\textgreater{} \\ \textless{}/response\textgreater{} \\ \textless{}/entry\textgreater{} \\ \textless{}/Bundle\textgreater{} \\ \hline \end{tabular}
\end{table}