QL4MDR: a GraphQL query language for ISO 11179-based metadata repositories

Abstract

Background: Heterogeneous healthcare instance data can hardly be integrated without harmonizing its schema-level metadata. Many medical research projects and organizations use metadata repositories to edit, store and reuse data elements. However, existing metadata repositories differ regarding software implementation and have shortcomings when it comes to exchanging metadata. This work aims to define a uniform interface with a technical interlingua between the different MDR implementations in order to enable and facilitate the exchange of metadata, to query over distributed systems and to promote cooperation. To design a unified interface for multiple existing MDRs, a standardized data model must be agreed on. The ISO 11179 is an international standard for the representation of metadata, and since most MDR systems claim to be at least partially compliant, it is suitable for defining an interface thereupon. Therefore, each repository must be able to define which parts can be served and the interface must be able to handle highly linked data. GraphQL is a data access layer and defines query techniques designed to navigate easily through complex data structures.

Results: We propose QL⁴MDR, an ISO 11179-3 compatible GraphQL query language. The GraphQL schema for QL⁴MDR is derived from the ISO 11179 standard and defines objects, fields, queries and mutation types. Entry points within the schema define the path through the graph to enable search functionalities, but also the exchange is promoted by mutation types, which allow creating, updating and deleting of metadata. QL⁴MDR is the foundation for the uniform interface, which is implemented in a modern web-based interface prototype.

Conclusions: We have introduced a uniform query interface for metadata repositories combining the ISO 11179 standard for metadata repositories and the GraphQL query language. A reference implementation based on the existing Samply.MDR was implemented. The interface facilitates access to metadata, enables better interaction with metadata as well as a basis for connecting existing repositories. We invite other ISO 11179-based metadata repositories to take this approach into account.

Keywords: GraphQL; HL7 FHIR; Interoperability; Metadata repository.

Fig. 1

Using metadata to support the integration of healthcare instance data. The process consists of the four stages: the metadata acquisition stage with a uniform interface enables to reuse of information which is stored in project-specific MDRs. The matching stage aligns the metadata and identifies potential correspondences. The mapping stage creates transformation rules, which are used in the transformation stage. The first three stages only process metadata, whereas the last transformation stage includes healthcare instance data

Fig. 2

The six defined entry points, separated into the identified metadata (lower part) and the formal description of the metadata (upper part). The three bold entities are suitable entry points for mutations. The right box shows an example query to request all data Data Elements containing a Slot with the name “SNOMED-CT” and the value “723,232,008” (average blood pressure). The query defines the representation of the response: each corresponding Data Element shall be returned with its identification and its definitions

Fig. 3

This sequence diagram shows the required messages between the GraphQL client (left) including the used query (box), the RESTful client (right) and the MDR server to receive the validation rules of each data element in a specific namespace. The GraphQL client needs only one query shown in the box, whereas the message amount of the RESTful client depends on the number on data elements associated with the chosen Namespace