Ken Schwaber is one of the creators of Scrum and he founded Scrum.org to help individuals and teams solve complex problems.
As can be seen from the description under Resources on Scrum.org, it is to be regarded as a framework.
Scrum is a lightweight framework that helps people, teams and organizations generate value through adaptive solutions for complex problems.
In Scrum requirements, all requirements are gathered in "Product Backlog" where they are detailed and refined until they are so clear and specific that they can be transferred to "Sprint Backlog".
Ken Rubin is one of the most widely read authors and hired educators in Scrum. Ken's company Innolution describes how to work in practice with "Product Backlog". An image describes the specific objects that a "Product Backlog Item" (PBI) can be broken down into:
In the study of Enterprise Architecture and the hierarchy of the implementation dimension, it is "Feature" and its breakdown into "User Story" and "Use Case" that is relevant.
These terms are not explained in the official Scrum glossary but there are several sources that describe their interpretation. Justinmind provides the following illustration and characteristics regarding size:
As can be seen from the picture, a "Use Case" is larger in scope as several sprints may be required, while a "User Story" can fit in one sprint. A quote from Justinmind's blog:
User stories are much briefer, more succinct documents and generally tend to be used for smaller features. They can also be used to break larger features down into small steps or multiple user stories. Conversely, use cases tend to give more of an overview of a larger system functionality.
Even before Prime Arch started mapping against the agile frameworks, the following article was published in the Prime Arch app: User story or Use case.
It corresponds very well with the above descriptions from Justinmind.
To proceed further in the analysis, a comparison of other established standards such as SAFe and Atlassian is required. The result of the overall analysis is described in the article "Implementation hierarchy in different standards".