Understanding the Structure of the RDA: A Librarian's Guide

December 18, 2025 •

4 min read

First published online in 2010, Resource Description and Access (RDA) succeeded the Anglo-American Cataloguing Rules (AACR2) as the modern cataloging standard for libraries. The structure of the RDA represents a fundamental shift toward the digital environment, basing its framework on a relational entity-relationship model to describe resources more flexibly and comprehensively for online users.

Quick Summary

Resource Description and Access (RDA) is a content standard built on the conceptual framework of FRBR and FRAD, organizing bibliographic data around entities like works, expressions, manifestations, and items (WEMI) and their relationships. This structure supports modern digital discovery while ensuring compatibility with existing library systems.

Key Points

Based on Entity-Relationship Models: RDA's structure is built on conceptual models like FRBR and FRAD, defining how entities, attributes, and relationships are recorded.
Organized Around WEMI: The core entities are Work, Expression, Manifestation, and Item, representing the abstract idea, its realization, its physical form, and a specific copy, respectively.
Explicit Relationships: A key feature is the ability to explicitly link entities, which supports advanced resource discovery and navigation for users.
User-Focused: The rules are designed to facilitate user tasks like finding, identifying, selecting, and obtaining information resources.
Data-Centric and Flexible: Unlike its predecessor, AACR2, RDA separates the data from its presentation, allowing it to be encoded in various formats like MARC, Dublin Core, and others.
Incorporates the LRM: The most recent version of the RDA Toolkit aligns with the IFLA Library Reference Model, which consolidates previous conceptual models.

The Conceptual Foundations of RDA

The structure of Resource Description and Access (RDA) is not an arbitrary set of rules but is derived from internationally recognized conceptual models developed by the International Federation of Library Associations and Institutions (IFLA). Primarily, it is based on the Functional Requirements for Bibliographic Records (FRBR) and Functional Requirements for Authority Data (FRAD). More recently, this foundational structure has been consolidated and modernized under the new IFLA Library Reference Model (LRM), though the core principles remain the same.

Functional Requirements for Bibliographic Records (FRBR)

FRBR defines the foundational entities representing the products of intellectual or artistic endeavor. These are often referred to by the acronym WEMI:

Work: A distinct intellectual or artistic creation, representing the abstract idea or concept of a resource. For example, Beethoven's Ninth Symphony as a musical composition.
Expression: The specific intellectual or artistic realization of a work. This could be the score written by Beethoven, a particular performance, or a translation of a book.
Manifestation: The physical or digital embodiment of an expression. This represents all copies that share the same publication characteristics, like a hardcover edition of a book or a specific DVD pressing of a film.
Item: A single, concrete copy or instance of a manifestation. A specific book in a library with a unique call number and barcode is an item.

Functional Requirements for Authority Data (FRAD)

FRAD provides the framework for authority data—information that establishes and controls access points, such as names of persons, families, and corporate bodies. These entities are responsible for the intellectual content or custodianship of Group 1 entities.

Group 2 Entities: Person, Family, and Corporate Body are responsible for creating or being associated with the resource.
Group 3 Entities: Concepts, Objects, Events, and Places are the subjects of the work.

Structure Based on Entities, Attributes, and Relationships

Following the FRBR and FRAD models, RDA organizes its instructions around these entities, their attributes, and their relationships. The original RDA documentation was formally structured into ten sections, with the first four focusing on attributes and the remaining on relationships. The modern, updated RDA Toolkit has moved to a more data-centric, element-based organization that is optimized for online use.

Attributes and Core Elements

Attributes are the characteristics used to describe an entity. For example, attributes of a manifestation include its title, publisher, and date of publication. RDA designates a set of minimum required attributes as "core elements" for resource description, ensuring consistency and comprehensiveness.

Relationships and Linked Data

A key strength of the RDA structure is its focus on explicit relationships between entities. It provides instructions for recording relationships between works, expressions, manifestations, items, and the people and organizations associated with them. This relational data model is crucial for enabling linked data, allowing library catalogs to connect to the broader web of data.

User Tasks

At its heart, the RDA structure is designed to help users complete specific tasks. The FRBR user tasks—Find, Identify, Select, and Obtain—are central to defining which data elements are mandatory and how they are applied. The FRAD tasks—Find, Identify, Justify, and Contextualize—relate to authority data.

The RDA Toolkit and the New Library Reference Model (LRM)

The RDA Toolkit is the official, online resource for the cataloging standard. It provides browsable and searchable instructions, workflows, and mappings to various encoding schemes like MARC 21. The “3R Project” modernized the Toolkit, incorporating the Library Reference Model (LRM), which unifies and replaces the earlier FRBR, FRAD, and FRSAD models. This element-based structure enhances flexibility and adaptability for the digital environment.

RDA vs. AACR2: A Structural Comparison


Feature	RDA (Resource Description and Access)	AACR2 (Anglo-American Cataloguing Rules, 2nd ed.)
Underlying Model	Relational model based on FRBR/FRAD/LRM.	Manual rules, hierarchical, based on the card catalog era.
Data Elements	Element-based; explicitly separates content, media, and carrier types. Uses specific, controlled vocabularies.	Uses General Material Designators (GMDs) that mix content and carrier types.
Resource Types	Treats all resource formats (analog and digital) in an integrated way.	Heavily favors print, with special rules for non-book formats.
Punctuation	Does not require ISBD punctuation; separates content from presentation.	Requires ISBD punctuation, making the cataloging record's display dependent on specific symbols.
Primary Focus	User tasks (Find, Identify, Select, Obtain) and explicit relationships.	Display of bibliographic data on a 3x5 card.
Authority Control	Based on the FRAD model, which expands on AACR2's approach to access points.	Less explicit; authority control instructions were less conceptually grounded.

Conclusion

The structure of the RDA is a purpose-built framework for the modern, digital information environment, moving library cataloging away from the limitations of the card catalog era. By adopting the principles of FRBR, FRAD, and now the LRM, RDA organizes resource data around logical entities, attributes, and relationships. This foundational structure provides a flexible, robust, and web-friendly standard that enhances resource discovery for users, integrates more smoothly with different metadata schemas like MARC and Dublin Core, and allows libraries to build more powerful and meaningful catalogs. The move from AACR2 to RDA represents a major evolution, shifting the focus from a prescribed, presentation-oriented process to a data-centric and user-focused standard, securing the relevance of library data in the age of linked information.

Visit the Library of Congress guide to RDA Core Elements

Frequently Asked Questions

The main difference is the underlying conceptual model. RDA is based on the relational FRBR and FRAD models, which define entities and relationships, making it more data-centric and flexible for digital resources. AACR2, in contrast, was structured around the rules required for the linear display of card catalogs.

WEMI refers to the Group 1 entities from the FRBR model: Work, Expression, Manifestation, and Item. The RDA structure is built around describing the attributes of these entities and the relationships between them, enabling a more granular and sophisticated approach to cataloging.

RDA explicitly supports the FRBR user tasks: Find, Identify, Select, and Obtain. By organizing data around entities and relationships, it allows for more precise searches and the grouping of related records, such as different formats or translations of the same work, making information discovery more intuitive.

Attributes are the characteristics that describe an entity (e.g., title, publisher). Relationships explicitly define how entities relate to one another (e.g., a person creating a work). The RDA structure is organized around recording both attributes and relationships to provide a richer, more interconnected bibliographic record.

Core elements are the minimum set of data elements required by RDA to create a basic, functional description of a resource. These were designated based on the FRBR and FRAD user tasks to ensure a consistent and sufficient level of descriptive metadata.

The RDA Toolkit is an online platform that provides the official RDA instructions and guidelines. It organizes content by entities and elements, allows searching, and maps RDA data to encoding schemes like MARC 21, helping catalogers apply the structured rules efficiently.

No, RDA is a content standard, while MARC 21 is a metadata encoding schema. The two are complementary. RDA provides the rules for formulating the descriptive data, and MARC provides the structure for encoding and communicating that data within library systems.