## 4 Discussion  
According to the identified need for better tooling in terms of SNOMED CT post-coordination, we successfully developed the versatile application WASP, which not only supports the creation of postcoordinated expressions (PCEs) in its rudimental form but also employs SNOMED CT Expression Templates for additional functionality. This includes both the creation of user-defined templates as well as their usage for PCE creation in turn. During the development process, great emphasis was laid on user guidance by providing necessary and comprehensible functionality and preventing erroneous input. The chosen approach benefits greatly from SNOMED CT's extensive formalisms. Existing specifications of the Compositional Grammar, Concept Model and Expression Templates were largely machine-processable and easily integratable, so that the application's compliance with the current definitions is ensured. The deep integration of these specifications into the application's architecture is pivotal for fulfilling the central goal of guaranteeing the syntactic and semantic correctness of user-created PCEs. While the successful achievement of this aim is a logical conclusion of WASP's design, it was also proven empirically using existing real-life examples. For the PCEs defined within the German MIOs, correct expressions could be successfully replicated in WASP using a roundtrip  
Figure 8: Results of the usability survey. validation based on Template generation and subsequent PCE creation. The replication of PCEs previously identified as incorrect was effectively prohibited. A small usability study supports these claims as well and indicates good user acceptance. Guidance through information fields within the application was received well, but further explanations, e.g., by providing a user manual, would still be beneficial to improve accessibility and to resolve any uncertainties. This huge need for information once again demonstrates the complexity of the PCE creation process and emphasizes our demand for better tooling. Furthermore, the complexity inherent in the whole topic of SNOMED CT postcoordination was omnipresent throughout the project. We encountered inaccuracies not only in existing user-created PCEs but also in the official specifications of the MRCM and several Expression Templates by SNOMED International. These were conjointly resolved, leaving a stable and quality-assured ground truth for PCE validation. On the other hand, these issues not being found earlier is indicative of the lacking usage of postcoordination in general. WASP can only contribute to a wider adoption by facilitating PCE creation; the integration of PCEs in electronic health records and their subsequent (re)use entails the need for further specialized software. In this context, the recent proliferation of HL7 FHIR works as a driving factor. FHIR resources build the syntactic fundament in which SNOMED CT is often prioritized for semantic standardization of individual data elements, creating a strong synergy between the two standards. This development is further fueled by FHIR's Terminology Module, which offers a standardized interface to query SNOMED CT content [40]. Putting this principle to work via a sophisticated terminology server facilitated a straightforward implementation of WASP and greatly reduced the amount of work required. There are several opportunities for future development in the context of WASP. The conducted usability study already yielded valuable input for improvement, which is progressively implemented. Yet, a larger user evaluation is required to gain broader feedback from users with different backgrounds, particularly domain experts in charge of designing PCEs. To facilitate such a survey, and primarily to broaden access, the web application is currently being made available to the public. Apart from minor functionality and stability improvements, larger adaptations of the PCE creation process available in WASP would also be imaginable.