Phase 4 Public Review

CDISC invites you to submit comments on the draft v4.0 of the Unified Study Definitions Model (USDM) during the 30-day Public Review period.

CDISC, in continued collaboration with TransCelerate’s Digital Data Flow Project, is updating the reference architecture, which will serve as a standard model for the development of a Study Definitions Repository. The Repository is a novel central component aimed at facilitating the exchange of structured study definitions across clinical systems using technical and data standards.

The focus of Phase 4 is:

• More focus on refinement rather than new content with development in the following areas:
  • Notes & Criteria
  • Activity Groups
  • Multiple Template Support (M11 alignment)
  • Abbreviations
  • Interventions, Identifiers & Roles (M11 alignment)
  • Amendments (M11 alignment)
  • Estimands (M11 alignment)
  • Observational & Device Studies
  • Final M11 alignment
• Attention to backward compatibility
• Maximum alignment with ICH M11
• Conformance Rule Specification Development

Deliverables include a logical data model, supporting Controlled Terminology, API specifications, Conformance Rule Specifications and an associated Implementation Guide. 

To Provide Comments:

• An information page on the draft USDM v4.0 for public review can be here. DDF Phase 4 Public Review Dashboard.
• Reviewers are requested to provide comments via JIRA. Detailed instructions on reviewing the document and using the Wiki and JIRA can also be found on this page. 
  DDF Phase 4 Public Review Dashboard   Public Review closes 3 April 2025

You will need to log in or register for the CDISC Wiki to provide comments.  

• Register for the Wiki. If you already have an account on Wiki or JIRA, our issue-tracking system, simply log in to your account; Wiki and JIRA use the same login credentials. CDISC Wiki is a different login from www.cdisc.org.

Public Review Workshops:

• CDISC conducted an initial Public Review workshop in Tuesday 04 Mar 2025. The recording and presentation materials are available on the DDF Phase 4 Public Review Dashboard.
• CDISC is conducting two additional Public Review workshops:
  • Tuesday 18 Mar 2025 11:00-12:00 US Eastern
  • Tuesday 25 Mar 2025 11:00-12:00 US Eastern
• These coincide with the DDF SME Meeting times. If you are not part of the SME group and want to join these workshops please contact John Owen (jowen@cdisc.org).

Public review is a key quality step in our Standards Development Process. CDISC relies on your input to ensure neutral, consensus-based data standards are developed and adopted by a diverse global community interested in improving research processes and quality for the benefit of all.

Thank you for contributing your time and expertise.

Watch this informational video to find out more about the USDM

The Unified Study Definitions Model contains the following artefacts:

Unified Study Definitions 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 that are 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 guidance to the solution implementer. It 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 the Minimal Viable Product. 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 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; these resource definitions represent the data exchange format for applications implementing the API.

The class diagram references industry standards and terminology systems where relevant. For example, the Study Definition class diagram includes references to CDISC Biomedical Concepts, Foundational Standards, and Controlled Terminology. The data dictionary accompanying the class diagram will include references to the CDISC Library for retrieval of all CDISC content. Content from other standards and terminology systems (HL7, LOINC, CPT, ICH M11, et al) may be incorporated into the LDM, with the intention of extending interoperability to data exchange standards, such as FHIR. The class diagram also depicts essential elements of a study protocol including study objectives, endpoints, and the schedule of activities. 
 

CDISC Controlled Terminology to Support USDM

The use of standardized terminology is an essential element of interoperability. To support the Study Definition LDM, CDISC will develop new Protocol Controlled Terminology, including code lists and terms as well as changes to existing terms, if needed. Terminology for SDTM Trial Design domains will also be covered in this project.

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 also publishes API specifications using these formats. The CDISC Library, 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.

The Study Definition API enables clients to create, update, and remove Study Definition content assuming the user’s role permissions support the activity. Accordingly, the API provides access to Study Definition services so that alternative user interfaces and applications can be developed to extend or exchange information with any given Study Definition tool. 
 

Unified Study Definitions Model Implementation Guide (USDMIG)

A new deliverable for the Digital Data Flow Reference Architecture v2.0 is a corresponding Implementation Guide. The Unified Study Definitions Model Implementation Guide (USDMIG) is intended for companies and individuals involved in the set-up of clinical studies—sponsors or stakeholders involved in upstream (protocol and content authoring tools)—and downstream consumers of system (e.g., electronic data capture, clinical trial management, trial master file) and document (e.g., protocol, clinical study reports, statistical analysis plans) standardized digitized study definitions.

This document provides users with sufficient information to understand the USDM and also its potential implementations with the study design process by showing examples of the types of study definition information that can be represented in the USDM.

Unified Study Definitions Model Implementation Conformance Rules

Conformance rules would be used to assert that any given Study Definition solution conforms to the DDF Study Definition Reference Architecture (RA). The availability of conformance tests will aid implementers to ensure solutions conform with the RA, purchasers to ensure products being acquired meet the requirements, and collaborating organizations to ensure that their study builds are interoperable at least in terms of the scope of the RA. Automated conformance tests provide a clarifying interpretation of the RA that supports the RA documentation and aids solution architects and implementers. CDISC CORE (CDISC Open Rules Engine) is an open-source software, which will execute machine-readable CDISC Conformance Rules retrieved from the CDISC Library. Conformance Rule specification development will run hand-in-hand with USDM standards development (similar to other CDISC standards).

We are looking for targeted reviewers of the draft deliverables throughout the development phase with particular expertise in the following areas:

• CDISC Protocol-related Controlled Terminology
• UML model review in relation to study/protocol concepts
• Technical skills to review API specifications in relation to study/protocol concepts
• Experience of this type of project within your own organization
• Solution providers who have technical ability to review updates to the USDM

Anticipated Timelines for Phase 5:

• May 2025 to April 2026

Public Review time commitment is estimated at 10-20 hours depending on experience with the four areas mentioned above. We encourage reviewers to reach out to colleagues who may also have experience in reviewing these types of deliverables or have business experience with this type of project. Please get in touch using the sign-up instructions below.

Participate

• If you would like to participate in this exciting effort, please follow the instructions below:
  • Targeted Public Reviewers: Sign up on the CDISC Volunteer page and indicate DDF as the Standards Development team. Please enter Targeted Internal and Public Reviewer in the box "Specify in which capacity you want to participate."
  • Participation in Standards Development: Sign up on the CDISC Volunteer page and indicate DDF as the Standards Development team. In the specify box enter in what capacity you feel you can contribute to the team and the amount of time you can contribute to the project.

The USDM Governance Group (UGG) plays a central role in ensuring the ongoing development, quality, and consistency of the Unified Study Definitions Model (USDM). As the model continues to evolve to support modern clinical study design and digital data flow, governance provides the structure and transparency needed to manage change effectively while reflecting the needs of a broad and diverse stakeholder community.

Watch the UGG introductory video to:

• Understand why Governance is Important
• Understand the UGG Process
• Learn How to submit a UGG Request

The UGG is founded on three key principles: inclusivity, accountability, and alignment.

• Inclusivity ensures that stakeholders across CDISC, industry initiatives, and the wider community can contribute to the evolution of USDM, helping the model reflect real-world needs.
• Accountability is achieved through clearly defined roles and responsibilities, supporting transparent and consistent decision-making.
• Alignment ensures that USDM evolves in harmony with initiatives such as Digital Data Flow (DDF) and ICH M11, reducing duplication and promoting interoperability across the clinical research ecosystem.

The UGG operates through a structured governance model that combines leadership, coordination, and subject matter expertise. The UGG Leadership Team provides strategic oversight and ensures alignment with broader CDISC priorities, while UGG Leads manage day-to-day governance activities and workflows. UGG Representatives form the core decision-making body, bringing domain expertise and community representation through a nomination-based process. Additional support is provided by Special Advisors, and the wider DDF/USDM community is engaged when broader consultation is needed.

The UGG manages a wide range of community-driven requests through a transparent process. Submissions are triaged, reviewed, and, where appropriate, shared for community feedback before a final decision is made. Approved requests are prioritized for inclusion in future USDM releases, while all outcomes are documented for transparency. Stakeholders can easily submit requests via the CDISC DDF website using the DDF Contact Us form, ensuring that feedback, improvements, and innovations can be continuously incorporated into the model.

Overall, the USDM Governance Group ensures that the evolution of USDM is community-driven, transparent, and strategically aligned. By combining structured processes with broad stakeholder engagement, the UGG enables USDM to grow in a consistent and sustainable way—supporting innovation while maintaining the integrity and interoperability that are essential to modern clinical research standards.

Keep up to date with current USDM development activities visit the participate tab and join the CDISC DDF/USDM community.

DDF Phase 4 Webinar

Watch the DDF Phase 5 Public Review Workshops located on the DDF Phase 4 Public Review Dashboard
Watch the DDF Phase 4 Informational Webinar

DDF Phase 3 Webinar
Watch the DDF Phase 3 Public Review Webinar
Watch the DDF Phase 3 Informational Webinar

DDF Phase 2 Webinar
Watch the DDF Phase 2 Public Review Webinar

DDF Phase 1 Webinar
Watch the DDF Phase 1 Public Review Webinar
Watch the Project Information and Call for Volunteers Webinar

Released Versions of the Unified Study Definitions Model (USDM)

Published Date: 27 June 2023

DDF Reference Architecture v2.0 Final

The Digital Data Flow Reference Architecture v2.0 has been released and is available via the Files tab on this page. Key elements include the Unified Study Definition Model (USDM) Class Diagram, the Application Programming Interface (API) Specification, associated CDISC Controlled Terminology, and, new for this release, the Unified Study Definition Model Implementation Guide (USDMIG).

In version 2.0, the USDM has been updated to accommodate more complex study designs, demonstrate population of an electronic protocol template, and expand the model to include a biomedical concept layer to aid in CRF automation.

The USDMIG provides users with sufficient information to understand the USDM and its potential implementations with the study design process by showing examples of the types of study definition information that can be represented in the USDM.

The Reference Architecture v2.0 has completed the CDISC Standards Development Process and is released as Final; the CDISC Controlled Terminology may not be final at the time of release. Additionally, DDF Phase 3 will start July 2023 and build on v2.0. To keep informed of Reference Architecture future enhancements, please attend the informational webinars. Please visit the CDISC RA GitHub Site for ongoing development of Phase 3 of the Digital Data Flow Reference Architecture.

CDISC and TransCelerate have collaborated to develop the USDM Reference Architecture in conjunction with development of a Study Definitions Repository (a reference Implementation of the USDM architecture). For more information on the Study Definitions Repository, please visit the TransCelerate DDF GitHub site and the SDR Github Site.

For any questions related to this release please get in touch using the Contact Us tab. Also if you are interested in becoming part of the DDF team please see the Participate tab for more information.

The DDF Reference Architecture contains the following:

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 that are 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 guidance to the solution implementer. It 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 the Minimal Viable Product. 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 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; these resource definitions represent the data exchange format for applications implementing the API.

The class diagram references industry standards and terminology systems where relevant. For example, the Study Definition class diagram includes references to CDISC Biomedical Concepts,  Foundational Standards, and Controlled Terminology. The data dictionary accompanying the class diagram will include references to the CDISC Library for retrieval of all CDISC content. Content from other standards and terminology systems (HL7, LOINC, CPT, ICH M11, et al) may be incorporated into the LDM, with the intention of extending interoperability to data exchange standards, such as FHIR. The class diagram also depicts essential elements of a study protocol including study objectives, endpoints, and the schedule of activities.  

CDISC Controlled Terminology to Support USDM

The use of standardized terminology is an essential element of interoperability. To support the Study Definition LDM, CDISC will develop new Protocol Controlled Terminology, including code lists and terms as well as changes to existing terms, if needed. Terminology for SDTM Trial Design domains will also be covered in this project.

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 also publishes API specifications using these formats. The CDISC Library, 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.

The Study Definition API enables clients to create, update, and remove Study Definition content assuming the user’s role permissions support the activity. Accordingly, the API provides access to Study Definition services so that alternative user interfaces and applications can be developed to extend or exchange information with any given Study Definition tool.

Unified Study Definition Model Implementation Guide (USDMIG)

A new deliverable for the Digital Data Flow Reference Architecture v2.0 is a corresponding Implementation Guide. The Unified Study Definitions Model Implementation Guide (USDMIG) is intended for companies and individuals involved in the set-up of clinical studies—sponsors or stakeholders involved in upstream (protocol and content authoring tools)—and downstream consumers of system (e.g., electronic data capture, clinical trial management, trial master file) and document (e.g., protocol, clinical study reports, statistical analysis plans) standardized digitized study definitions.

This document provides users with sufficient information to understand the USDM and also its potential implementations with the study design process by showing examples of the types of study definition information that can be represented in the USDM.

USDM Onboarding Package

USDM Onboarding Package Course Page

The CDISC USDM Schedule of Activities (SoA) Project

Advancing Clinical Research Through Digital Standards 

Clinical research is undergoing a transformation. As the complexity and volume of data increases, the need for standardized, digital, and interoperable data frameworks has never been greater. The CDISC USDM Schedule of Activities (SoA) Project sits at the centre of this change—helping to modernize how clinical studies are designed, managed, and executed.

From Documents to Data: A Step Change in Clinical Trials

Traditionally, clinical trial protocols—and particularly the Schedule of Activities—have been managed as static documents. This approach creates inefficiencies, manual interpretation, and duplication of effort.

The Digital Data Flow initiative introduces a data-first approach, where structured protocol information is:

• Reusable across systems
• Interpretable by machines
• Accessible to different stakeholders through role-based views

This shift enables:

• Faster study start-up and execution
• Improved study design and efficiency
• Increased capacity to run more trials at higher quality

The Role of the USDM Standard

At the heart of this transformation is the Unified Study Definitions Model (USDM)—a CDISC standard that provides a structured representation of clinical study design.

USDM provides a comprehensive and structured foundation for representing clinical study design in a consistent, digital format. It brings together a logical data model that clearly defines all key study elements, ensuring that complex protocols can be represented in a standardised and reusable way. This is reinforced through the use of controlled terminology, which promotes consistency and shared understanding across organizations and systems. In addition, USDM supports modern, connected workflows by enabling system-to-system communication through APIs, allowing study information to be exchanged seamlessly between technologies. To ensure successful adoption and consistent implementation, the standard is also supported by detailed guidance and validation rules, helping organisations apply it correctly while maintaining data quality and compliance.

The USDM captures all key aspects of a clinical study, including:

• Study design, timelines, and logic
• Population and eligibility criteria
• Interventions and procedures
• Objectives and endpoints

Critically, USDM enables the digitization of study timelines and activities, forming the foundation for modernizing the Schedule of Activities.

Introducing the USDM SoA Project

The USDM Schedule of Activities (SoA) Project has been launched to address a key industry challenge:
"how to move from static, ambiguous schedule tables to structured, computable data."

Project Objectives

The project is focused on:

• Defining industry-aligned implementation practices for SoA
• Bridging the gap between the USDM model and real-world use
• Standardising how schedules are represented
• Enabling automation and interoperability across systems

What the Project Will Deliver

The USDM SoA Project will produce practical, industry-driven outputs, including:

• Guidance for representing schedules using USDM
• Standard approaches to timing (e.g. study days, cycles, event-based schedules)
• Definitions for visits, scheduling windows, and anchor points
• Controlled terminology and metadata conventions
• Real-world examples and reusable templates

These deliverables will ensure that organisations can implement the Schedule of Activities in a consistent and scalable way while maintaining alignment with CDISC standards.

Why This Matters

Standardising and digitising the Schedule of Activities will unlock significant benefits:

For Research Teams

• Reduced reliance on free text and manual interpretation
• Clear, unambiguous study schedules
• Improved collaboration across functions

For Systems and Technology

• Seamless integration across CTMS, EDC, and analysis platforms
• Automation of study setup and execution
• Real-time validation and deviation detection

Built Through Collaboration

The USDM SoA Project is a community-driven initiative, led by CDISC with strong collaboration across the industry, including:

• Pharmaceutical and biotech organisations
• Clinical operations and data management teams
• Technology providers and vendors
• Standards experts and researchers

The project builds on prior work contributed by industry partners and follows a structured governance model to ensure:

• Transparency
• Consensus-based decision making
• Alignment with broader regulatory and standards initiatives

Get Involved

Success depends on broad community participation. The project is actively seeking contributors with expertise in:

• Clinical operations and study design
• Data standards (CDASH, SDTM, ADaM)
• Digital health technologies and data collection
• Systems implementation and integration

By participating, you can:

• Help shape the future of digital clinical trials
• Contribute to industry-wide standards
• Ensure practical, real-world applicability

Levels of Involvement

• Industry co-lead (~20% FTE)
  • Actively work with CDISC lead to plan and progress the project to publication
  • Plan and attend weekly team and monthly all-hands meetings
  • Provide expertise in the development of the standard
• Active Contributor (~3-4 hours/week)
  • Attend weekly team and monthly all-hands meetings
  • Provide expertise in the development of the standard
  • Participate in the Internal and Public Review of the standard
• Reviewer (~1 hour/week)
  • Attend Monthly all-hands meetings
  • Provide expertise in the Internal and Public Review of the standard

If you would like to participate in this exciting effort, please sign up on the CDISC Volunteer page and indicate "USDM SoA" as the Standards Development team. Please enter some information about your interest in the project in the "Specify in which capacity you want to participate."

Looking Ahead

The USDM SoA Project is a critical step toward a fully digital clinical research ecosystem—where study designs are no longer locked in documents but exist as structured, reusable, and intelligent data.

Together with USDM and Digital Data Flow, it represents a move toward:

• Faster trials
• Better data
• Improved outcomes for patients worldwide

Volunteering

Relationship to other Standards

Scope

Technology

About UGG

The USDM Governance Group provides oversight, decisionmaking, and strategic direction for the USDM. Members help ensure that changes to the standard are:

• Well reasoned and technically sound
• Aligned with stakeholder needs
• Supportive of the broader Digital Data Flow vision
• Consistent with CDISC’s commitment to interoperability and community-driven standards

UGG members serve a one year term, with the option for renomination.

Who Should Apply

We welcome nominees who bring:

• Strong analytical and critical thinking skills
• Ability to evaluate technical proposals objectively
• Experience synthesizing stakeholder perspectives
• Clear communication and collaborative decision making skills
• Familiarity with USDM concepts, DDF principles, and the digital protocol lifecycle
• Awareness of clinical study design and interoperability standards

A full list of competencies and expectations is included in the Nomination Information Sheet.

Time Commitment

Members are expected to participate in:

• 1–2 one-hour meetings per month outside development cycle
• Up to 4 one-hour virtual meetings per month during active development cycles
• Ongoing offline review of proposals, clarifications, and change requests

Participation in the CDISC DDF SME biweekly meeting is encouraged for items with broad stakeholder impact.

How to Nominate

Please complete the UGG Nomination Form

Nominations will be reviewed by the UGG Leadership Team (UGG-LT) in consultation with the UGG Team Leads. Selected nominees will be contacted with next steps, including onboarding and orientation.

Why Participate

Serving on the UGG is an opportunity to:

• Shape the future of digital protocol standards
• Represent your stakeholder community
• Contribute to a shared, community-driven model
• Support the advancement of end-to-end digital data flow across the industry