Research area hierarchy refers to the organization and categorization of different fields of study within a particular discipline or subject area. This hierarchical structure helps to classify and understand the various research areas and subfields within a specific domain. At the top of the research area hierarchy, we have the broadest and most general research areas or disciplines, such as humanities, social sciences, natural sciences, and engineering. These major categories encompass a wide range of subfields and topics. Within each major research area, there are more specific subfields or research areas, which further specialize and focus on particular aspects of the discipline. For example, within the field of social sciences, subfields may include psychology, sociology, economics, political science, and anthropology. Further down the research area hierarchy, there are even more specialized subfields and topics, often referred to as research topics or research themes. These areas of study delve deeper into specific subjects, theories, methodologies, or applications within a particular subfield. Overall, research area hierarchy helps to create a structured framework for organizing and understanding the different levels of research areas, subfields, and topics within a discipline or subject area. This hierarchy allows researchers to locate and explore relevant literature, collaborate with others in their field, and identify gaps in knowledge for further research.