O - Ontology, a structured classification value
Code of field: O
Type of field: a structured classification value.
Applicable to:
Any kind of structured hierarchy.
Comments:
Ontology fields deal with questions concerning what entities exist, and how such entities can be grouped, related within a hierarchy, and subdivided according to similarities and differences.
The kind of data managed from an OField can be absolutely anything.
The ontology structure can be viewed as a tree with branches and sub-branches without limit in depth.
The most global set is called the root.
A typical application could be a geographical structure where the root contains continents.
Each continent contains countries, each country contains counties, regions, provinces, which in turn contain entities, cities and villages, etc. down to any detailed level of items.
Another typical structure is wildlife classification, from the Kingdom to the Strain level, with intermediate branches like Orders, Classes, Families, Species, etc.
In practice, all the items are stored in a single table.
One OField is used to define one classification.
Multiple OFields can be defined in the same table to describe different classifications.
For example, a first OField could give the geographical tree, where a second OField could give the geological tree of the same entities.
It is very important to notice that all levels must NOT be used.
So if a country has no province or county, this is not a problem.
The number of levels can be different for each record.
For example, some organisms have no Subfamily level. All records in that case will simply point to the Family level.
The only constrain is that, for one given OField, each record can have one and only one parent.
OFields are stored in the database under three columns.
Making changes by hand to any of these columns may give unpredictable results.
As each records keeps in mind its complete path from the root to its parent, moving records from one parent to another may take some time.
For example, changing the path of a city will automatically change the path of all child records of that city, as well as the path of all descendant records.
This is not a common operation, though.
This movie shows how to manage ontology data in BioloMICS.