Ensuring the FAIRness (Findable, Accessible, Interoperable, Reusable) of data and metadata is an important goal in both research and industry. Knowledge graphs and ontologies have been central in achieving this goal, with interoperability receiving much attention. The European Open Science Cloud initiative distinguishes in its Interoperability Framework (EOSC IF) four layers of interoperability: technical, semantic, organizational, and legal. This paper argues that the emphasis on machine-actionability has overshadowed the essential need for human-actionability of data and metadata, and provides three examples that describe the lack of human-actionability within knowledge graphs. In response, the paper propagates the incorporation of cognitive interoperability as another vital layer within the EOSC IF and discusses the relation between human explorability of data and metadata and their cognitive interoperability. It suggests adding the Principle of human Explorability, extending FAIR to the FAIREr Guiding Principles. The subsequent sections present the concept of semantic units, elucidating their important role in enhancing the human explorability and cognitive interoperability of knowledge graphs. Each semantic unit can be displayed in a user interface either as a mind-map-like graph or as natural language text. Semantic units organize knowledge graphs into levels of representational granularity, distinct granularity trees, and diverse frames of reference. Semantic units can be represented as FAIR Digital Objects (FDOs) that instantiate corresponding FDO classes. Various categories of FDOs are distinguished. The development of innovative user interfaces enabled by FDOs that are based on semantic units would empower users to access, navigate, and explore information in knowledge graphs with enhanced efficiency.

翻译：确保数据和元数据的FAIR性（可发现、可访问、可互操作、可重用）是研究与工业领域的重要目标。知识图谱和本体在此目标的实现中居于核心地位，其中互操作性受到广泛关注。欧洲开放科学云计划在其互操作性框架中区分了四个互操作性层次：技术层、语义层、组织层和法律层。本文认为，当前对机器可操作性的强调遮蔽了数据与元数据对人类可操作性的本质需求，并通过三个实例描述了知识图谱中人类可操作性的缺失现状。为此，本文主张将认知互操作性作为EOSC互操作性框架的另一关键层次，并探讨数据与元数据的人类可探索性与其认知互操作性之间的关系。文章建议增加人类可探索性原则，将FAIR扩展为FAIREr指导原则。后续章节提出语义单元的概念，阐明其在增强知识图谱的人类可探索性与认知互操作性方面的重要作用。每个语义单元可在用户界面中显示为类思维导图的可视化图谱或自然语言文本。语义单元将知识图谱组织为不同表征粒度层级、独立的粒度树及多样化的参照框架。语义单元可实例化为对应FAIR数字对象类的FAIR数字对象。本文区分了多种FAIR数字对象类别。基于语义单元的FAIR数字对象所实现的创新用户界面，将使用户能够以更高效率访问、导航和探索知识图谱中的信息。