Unified Study Definition Model (USDM) Class Diagram

The USDM Class Diagram is a UML class diagram that functions as the Study Definitions logical data model (LDM). The class diagram as LDM depicts the classes and attributes that represent data entities and the relationships between those entities needed to support a conformant Study Definitions application. The class diagram includes a data dictionary that defines each of the classes and attributes to provide the semantics needed to implement the model consistently.

The purpose of the LDM is to provide a normative standard to the solution implementer in order for them to create and implement a physical model. The LDM does not attempt to be inclusive of every class, attribute, and relationship implemented by any given solution. Instead, the LDM describes all elements for a conformant solution based on Release 1 and 2. It provides input into the solution architecture with the expectation that every effort will be made to ensure the solution architecture aligns with the RA LDM. The LDM represented by the class diagram may be implemented in a variety of physical data stores, including relational databases, property graph databases, RDF triple stores, document databases, and others. The semantics represented in the LDM and its data dictionary support a uniform understanding of the Study Definition data elements to improve interoperability. The LDM will be used to define the resources available in the API specification, and these resource definitions represent the data exchange format for applications implementing the API.

The class diagram references both CDISC and non-CDISC industry standards and terminology systems where relevant. It will be developed for compatibility with all other existing CDISC Standards that model protocol concepts, to ensure consistent terminology and relationships are used in USDM. Where the class diagram references external standards, CDISC will document these connections in order to help explain to the user community the provenance of the links. For example, the Study Definition class diagram includes references to new CDISC Biomedical Concepts, CDISC foundational standards, as well as CDISC controlled terminology. The data dictionary built into the class diagram will include references to the CDISC Library for retrieval of all CDISC content. Content from other standards and terminology systems will be incorporated where appropriate into the LDM, such as HL7, LOINC, Common Protocol Template, ICH M11, and others, either directly or through external linking, with the intention of extending interoperability in the future to data exchange standards such as HL7 FHIR. The class diagram also depicts essential elements of a study protocol including but not limited to study objectives, endpoints, and the schedule of activities (SoA).

CDISC Controlled Terminology to Support USDM

The use of standardized terminology is an essential element of interoperability. CDISC currently leads the Protocol Terminology project which develops the semantics for commonly used research protocol entities. CDISC works in collaboration with the NCI Enterprise Vocabulary Services and CDISC volunteer subject matter experts to develop this controlled terminology package. The Protocol Terminology project supports the CDISC foundational standards for the Protocol Representation Model (PRM) and Clinical Trial Registry XML (CTR-XML). New control terminology needed to support the Reference Architecture will be developed with reuse of terminology already developed for the protocol terminology package and other CDISC controlled terminology packages as appropriate. This updated Reference Architecture controlled terminology package will be published as a standalone package alongside other CDISC Controlled Terminology.

Application Programming Interface (API) Specification

A standardized API provides a standard interface for a common set of core services that must be supported by all conformant solutions. A standard API will enable application developers to build solutions that can use the core services of any conformant Study Definition. Data standards, controlled terminology, data exchange standards, and APIs work together to create an optimal environment for interoperability between conformant systems.

A Study Definition REST API will be specified using the OpenAPI Specification (OAS) version 3.0. As a machine-readable format, OAS can be used to generate not only interactive documentation, but also source code to aid developers creating software implementing the specification. The CDISC Library and ODM v2.0 also publish API specifications using these formats. The CDISC Library, ODM v2.0, HL7 FHIR, and the DDF Study Definition API form a growing set of standard APIs to improve interoperability and automation in clinical trials. Much like the CDISC Library API, the Study Definition API will support a range of media types including JSON and XML.

In addition to providing an interface for applications to retrieve study design information, the Study Definition API enables clients to create, update, and remove Study Definition content assuming the user’s role permissions support the activity. Thus, the API provides access to Study Definition services such that alternative user interfaces and applications can be developed to extend or exchange information with any given Study Definition tool.

USDM Implementation Guide

A CDISC Implementation Guide will guide the organization, structure, and format of CDISC standards and provide users with the information required to successfully implement a CDISC standard. The USDM Implementation guide will therefore inform users about implementation of the Unified Study Definition Model (USDM) Class Diagram, CDISC Controlled Terminology to Support USDM, and Application Programming Interface (API) Specification. The USDM Implementation Guide should be used alongside the other deliverables in order to fully understand and enable users to implement the USDM model.