Making data and metadata FAIR (Findable, Accessible, Interoperable, Reusable) has become an important objective in research and industry, and knowledge graphs and ontologies have been cornerstones in many going-FAIR strategies. In this process, however, human-actionability of data and metadata has been lost sight of. Here, in the first part, I discuss two issues exemplifying the lack of human-actionability in knowledge graphs and I suggest adding the Principle of human Explorability to extend FAIR to the FAIREr Guiding Principles. Moreover, in its interoperability framework and as part of its GoingFAIR strategy, the European Open Science Cloud initiative distinguishes between technical, semantic, organizational, and legal interoperability and I argue to add cognitive interoperability. In the second part, I provide a short introduction to semantic units and discuss how they increase the human explorability and cognitive interoperability of knowledge graphs. Semantic units structure a knowledge graph into identifiable and semantically meaningful subgraphs, each represented with its own resource that instantiates a corresponding semantic unit class. Three categories of semantic units can be distinguished: Statement units model individual propositions, compound units are semantically meaningful collections of semantic units, and question units model questions that translate into queries. I conclude with discussing how semantic units provide a framework for the development of innovative user interfaces that support exploring and accessing information in the graph by reducing its complexity to what currently interests the user, thereby significantly increasing the cognitive interoperability and thus human-actionability of knowledge graphs.

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