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A represents an association between two .

Each is identified by a unique Id and is distributed as a row in the Relationship file.

A contains of two logically associated and the of another that indicates the by which they are associated.

Table 1. Example: Defining arthritis as a type of joint disorder







In human readable terms...


|is a|

|joint disorder|

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Relationships and concept definitions

Each in is logically defined through its to other .

Every (except the ) has at least one |is a| to a supertype .

|is a| and defining attribute are known as the of . They are considered defining because they are used to logically represent a by establishing its with other . This is accomplished by establishing |Is a| with one or more defining (called supertypes) and modeling the difference with those supertypes through defining attributes.

Example: |Fracture of tarsal bone (disorder)| is defined as:

Note: A is assigned only when that is always known to be true.

Example: Group A Streptococcus causes most cases of Streptococcal pharyngitis. However, a small percentage of these cases are caused by other species of Streptococcus. Therefore, it would be incorrect to define |Streptococcal sore throat (disorder)| as having |causative agent| |Streptococcus pyogenes (organism)| . Instead it is correctly defined as having the more general |causative agent| |Genus Streptococcus (organism)| .

IS A Relationships

|is a| are also known as "Supertype - " or "Parent - ". |is a| are the basis of 's hierarchies, as illustrated below.

Figure 2. Example IS A hierarchy

A can have more than one |is a| to other . In that case, the will have parent in more than one of a top-level . can be multi-hierarchical.

Figure 3. Example IS A Relationships

Attribute Relationships

An is an association between two that specifies a of one of the (the source of the ). Each has a name (the type of ) and a value (the destination of the ).

The combination of the and |is a| associated with a represent the logical definition of that . Therefore, the logical definition includes one or more supertypes (represented by |is a| ), and a set of defining that differentiate it from the other definitions.


Since pneumonia is a disorder of the lung, the logical definition of the |Pneumonia (disorder)| in includes the following . The |Finding site| is assigned the value |Lung structure (body structure)| .

The full definitions of the |Pneumonia (disorder)| ,|Infective pneumonia (disorder)| and |Bacterial pneumonia (disorder)| are shown below. Each line represents a defining with a value.

Figure 4. Definition of |Pneumonia (disorder)|

Figure 5. Definition of |Infective pneumonia (disorder)|

Figure 6. Definition of |Bacterial pneumonia (disorder)|

illustrates some of these graphically. |is a| relate a to more general of the same type. In contrast, (such as |Finding site| and |Causative agent| ) relate a to relevant values in other branches of the .

Figure 7. Illustration of Defining Relationships

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