The ontology behind ICD-11: entities, parents and linearizations

One network, many lists

ICD-11 is built as a network of entities. The lists we code from are cut from it.

What the network holds

The network holds entities. Each has a title and a place in the hierarchy. Each has textual definitions and the terms people use for it. And each has machine-readable properties, such as anatomy and morphology, with values drawn from standard value sets. WHO's content model describes every entity in the same way.

• Title · Concept title · Each entity has a title, and a place in the hierarchy.
• Description · Definitions · Textual definitions and the terms people use for it.
• Properties · Values · Machine-readable properties, such as anatomy and morphology, with values from standard value sets.

More than one parent

An entity can have more than one parent. Oesophageal cancer can sit under neoplasms, and under digestive conditions. But in a tabular list each category has exactly one parent, and categories don't overlap. Multiple parenting is what lets one entity serve several purposes.

Lists derived from the foundation

A linearization is a list derived from the foundation. The mortality and morbidity list is one. There are specialty lists too, for example for primary care, dermatology and mental health. The coding scheme of an entry stays the same as in the full international classification.

• Common source · Foundation · Linearizations are derived from the same Foundation Component.
• Examples · Specialty · For example primary care, dermatology and mental health lists.
• The code · Unchanged · The coding scheme of an entry remains the one used for the full international classification.

In the foundation, not always in the list

WHO uses the image of a shoreline. Every entity is in the foundation and searchable there, but not every entity is visible as a stem code in the mortality and morbidity list. Extracting an entity into a classification doesn't alter its meaning.

• Everything · Searchable · All ICD entities are included and searchable in the Foundation.
• But · Not all coded · They may not be visible as stem codes in a classification such as the MMS.
• Meaning · Unaltered · Extracting an entity into a classification does not alter its meaning.

Entities are language independent

One last point. ICD-11 entities are language independent. Any language can be bound to them, which makes translation and multilingual browsing easier.

• The entity · No language · An entity is language independent.
• Any language · Bound · Any language can be bound to the elements of the Foundation, which makes translation and multilingual browsing easier.

Check yourself

Pause and think. In a tabular list, how many parents does each category have? The answer: One. In a tabular list the categories are mutually exclusive and jointly exhaustive and linked to a mono-hierarchical tree. Multiple parents are kept in the Foundation Component.

• One
• Two
• As many as the Foundation Component gives it
• None: parents exist only in the index

Keep these in mind

The foundation is a network of entities. An entity can have several parents there. Lists are derived from it, and in a list a category has one parent. And you code from a list, not from the foundation.

• The foundation is a network of entities
• An entity can have several parents there
• Lists are derived from it; a list category has one parent
• You code from a list, not the foundation