`SubClassOf`

vs `EquivalentTo`

¶

## Prerequisites¶

This lesson assumes you have basic knowledge wrt ontologies and OWL as explained in:

`SubClassOf`

¶

In this section we explain the semantics of `SubClassOf`

, give an example of using `SubClassOf`

and provide guidance for when not to use `SubClassOf`

.

### Semantics¶

If we have

```
Class: C
SubClassOf: D
Class: D
```

the semantics of it is given by the following Venn diagram:

Thus, the semantics is given by the subset relationship, stating the `C`

is a subset of `D`

. This means every individual
of `C`

is necessarily an individual of `D`

, but not every individual of `D`

is necessarily an individual of `C`

.

### A concrete example¶

```
Class: Dog
SubClassOf: Pet
Class: Pet
```

which as a Venn diagram will look as follows:

### Guidance¶

There are at least 2 scenarios which at first glance may seem like `C SubClassOf D`

holds, but it does not hold, or
using `C EquivalentTo D`

may be a better option.

- This is typically where
`C`

has many individuals that are in`D`

, but there is at least 1 individual of`C`

that is not in`D`

. The following Venn diagram is an example. Thus, to check whether you may be dealing with this scenario, you can ask the following question: Is there any individual in`C`

that is not in`D`

? If 'yes', you are dealing with this scanario and you should**not**be using`C SubClassOf D`

.

- When you have determined that (1) does not hold, you may deal with the scenario where not only is every individual of
`C`

in`D`

, but also every individual in`D`

is in`C`

. This means`C`

and`D`

are equivalent. In the case you rather want to make use of`EquivalentTo`

.

`EquivalentTo`

¶

## Semantics¶

If we have

```
Class: C
EquivalentTo: D
Class: D
```

this means the sets `C`

and `D`

fit perfectly on each other, as shown in the next Venn diagram:

Note that `C EquivalentTo D`

is shorthand for

```
Class: C
SubClassOf: D
Class: D
SubClassOf: C
```

though, in general it is better to use `EquivalentTo`

rather than the 2 `SubClassOf`

axioms when `C`

and `D`

are equivalent.

### A concrete example¶

We all probably think of humans and persons as the exact same set of individuals.

```
Class: Person
EquivalentTo: Human
Class: Human
```

and as a Venn diagram:

### Guidance¶

When do you not want to use `EquivalentTo`

?

- When there is an individual of
`C`

that is not in`D`

.

- When there is an individual of
`D`

that is not in`C`

.