# Ontological Relationships¶

In most cases, these relationships will be introduced by the BEL Namespace resources, and are not needed for creation of BEL Statements and BEL Scripts.

## Parent/Child¶

For terms A and B, `A isA B`

indicates that A is a subset of B.

All terms in BEL 1.0 represent classes, but given that classes implicitly have
instances, `A isA B`

is interpreted to mean that any instance of A must also be
an instance of B. This relationship can be used to represent GO and MeSH
hierarchies:

```
pathology(MESH:Psoriasis) isA pathology(MESH:"Skin Diseases")
```

## Whole/Part¶

For terms A and B, `A partOf B`

indicates that A is a part of B.

```
p(HGNC:CHUK) partOf complex(GO:"IkappaB kinase complex")
p(HGNC:IKBKB) partOf complex(GO:"IkappaB kinase complex")
p(HGNC:IKBKG) partOf complex(GO:"IkappaB kinase complex")
```

## Equivalence¶

For terms A and B, `A equivalentTo B`

/ `A eq B`

indicates that A and B are equivalent.
This relationship is two-way.