## 2 Background and Related Work
### Service-Oriented Architecture (SOA)  
According to the norms and standards of service-oriented quality [33; 34], SOA was one of the most used software architectural approaches in the early 2000s; it was used for the design and development of applications as services. This architecture aims to provide uniformity in the design, implementation and invoking of services required to meet the desired needs of the application [35]; that is, any process, subprocess or logic of an organization can be encapsulated in services [36]. As can be inferred, SOA is a business-focused information technology (IT) architecture that is supported by the integration of services. Consequently, all the services designed in SOA must comply with the following three fundamental software attributes [37; 38]: First, each developed component must have the ability to be reused within the application (reusability). Second, the components must be able to communicate with each other or with other external applications (interoperability). Third, the application must allow the ability to adapt to future needs or objectives of the organization (extensibility). As a follow-up to this activity, several research projects that propose the combined use of this architectural pattern with several software attributes will be outlined below, focused on various eHealth scenarios. For example, [PERSON] et al. [38] propose a novel conceptual model of EHR focused on the aspect of cross-border interoperability [39], whose objective is to meet the needs of interconnectivity between the different eHealth systems of Macedonia, under the specifications of the European Patients Smart Open Services project [40; 41]. Thus, the authors chose to combine the SOA architectural pattern with the use of the data warehouse (DW) and the following three technologies oriented to an extract, transform and load (ETL) process: the interface description (using Web services description language (WSDL) documents), the communication protocol simple object access protocol (SOAP) (using extensible markup language (XML)) and universal description, discovery and integration (UDDI) repositories (allowing users to find services) [38]. They have shown that the proposed model achieves a successful data exchange between the various platforms tested. Additionally, this model allows the classification and indexing of the data, which allows SOA to be able to communicate with different applications other than the predefined DW because each healthcare system is designed, implemented and validated by the HL7 fast healthcare interoperability resources (FHIR) protocol. Likewise, [PERSON] et al. [39] propose building a framework for the exchange of information among the eHealth systems of Indonesia, whose purpose is to integrate and synchronize data from different (heterogeneous) platforms through web interoperability. This framework was designed under the concept of service-oriented analysis and design (SOAD) [42; 43], which is composed of the three main phases of the conceptual view (CV), which illustrates to those involved all the activities that encompass the workflow of the organization; the logical view (LV), which encapsulates all the logic identified by the CV in various software services; and the physical view (PV), which implements the different web layers, including the presentation, application service, domain model and data access layers. The three previous phases focus on a logic based on SOA, whose objective is to process all user information and exchange data among platforms using the RESTful protocol [44]. They validated their framework by successfully relating eHealth systems and integrated entities and the exchange of data and information in the form of an interoperability matrix (IM), so that organizations can use this matrix as a point of reference for adaptation. [PERSON] et al.