WIP: start working on custom ontology doc

docs/source/index.rst

@@ -13,6 +13,7 @@ Welcome to APIS's documentation!
    :caption: Documentation:
 
    installation
+   ontology
    configuration
    user_documentation
    data_model

docs/source/ontology.rst

@@ -0,0 +1,26 @@
+Set up your ontology
+====================
+
+APIS provides two main types: entities and relations. Entities are things, whereas relations are the connections between things.
+To define your own entities and relations, we use `Django models <https://docs.djangoproject.com/en/4.2/topics/db/models/>`_.
+
+Entities
+--------
+
+To create entities, define them in your application and let them inherit from :class:`apis_core.apis_entities.models.AbstractEntity`
+Like with any other Django model, you can define fields describing the attributes of this entity:
+
+.. code-block:: python
+
+   from apis_core.apis_entities.models import AbstractEntity
+
+   class Person(AbstractEntity):
+       name = models.CharField(max_length=255, help_text="The persons´s name", blank=True, null=True)
+
+
+   class Place(AbstractEntity):
+       lat = models.FloatField(blank=True, null=True, verbose_name="latitude")
+       lng = models.FloatField(blank=True, null=True, verbose_name="longitude")
+
+For every entity you define, there will be a menu entry in the main APIS menu, pointing to a list of instances of this entity. In
+this list it is possible to filter entities based on their defined attributes.