Hierarchical relationship is the broader and narrower relationship between concepts. It is based on higher and lower levels in the hierarchy, where the higher hierarchical terms represent a class and the subordinate terms refer to its members.It should be established between a pair of concepts when the scope of one of them totally includes the scope of the other.
The hierarchical relationship functions to clarify the scope of the concepts by placing them in the appropriate hierarchical branch.
Itis the primary feature that distinguishes a thesaurus or taxonomy from simple controlled lists and dictionaries. In a simple list, for example we can have the terms “Storage Vessels” and “Amphorae”. The fact that the Amphora is a storage vessel is not indicated anywhere, it is knowledge that the user should have. In a thesaurus this relationship is clearly stated as amphorae are classified as narrower terms in storage vessels
The following tags should be used:
BT (broader term), written as a prefix to the superordinate term.
NT (narrower term), written as a prefix to the subordinate term.
There are three types of hierarchical relationships:
Genus/Species relationships
It is the relationship between a class or category and its members or species. This relationship is often called “IsA”. All children in this relationship should be a kind of, or type of the parent. The placement of a child may be tested by the all/some argument. E.g. some members of the class “Felines” are known as “Cats” , and all “Cats” by definition and irrespective of context, are regarded are “Felines”.
Figure: Some felines are cats, all cats are felines. These terms should be place in the same hierarchy.
Figure: Some pets are cats, some cats are pets. These terms should not be placed in the same hierarchy.
Whole/Part relationships
The hierarchical whole/part relationship refers to concepts , which are inherently included in another, regardless of context. Whole/part relationships are typically applied to geographic entities, parts of the body, disciplines of study, social structures and other types of concepts that are not readily placed into genus/species relationships. Each child should be a part of the parent and all the other ancestors above it.
Example: Social sciences
NT Anthropology
NT Sociology
Instance relationships
It is the relation that identifies the link between a general category and the individual instances of that category.
Polyhierarchical relationships
Some concepts logically belong to more than one class at the same time. This means that they have more than on broader term. In such cases, a hierarchical link should be established to all of the appropriate broader terms.
The structure that contains terms that have more than one broader terms is said to be polyhierarchical.
Figure: Example of polyhierarchical structure.
Figure: Example of polyhierarchical structure. From AAT Getty. Term ID=300138750
Guide terms in hierarchies
Guide terms are phrases, usually placed in angle brackets, that are used to group together similar terms. They typically indicate the principles of division among a set of sibling terms.
Example: Car
|
<by motive power> |
<by purpose> |
| Diesel cars | Racing cars |
| Electric cars | Sports cars |
