# Basic Geometry Representation

I have an assignment in my introduction to database course. I chose to try and do a database model to represent basic geometric figures and mathematical objects (functions, polynomes, etc). For example, my db should be able to store (partially) what you can make with a software like GeoGebra (https://www.geogebra.org/classic).

I am doing an ERD, but I have some problems representing relations and entities... The base of my model is the entity Point with three attributes label, x and y. I am having troubles representing figures that are solely composed of Point, but that can contain more Point, e.g.. polygons (composed of N > 3 points, and there can be points INSIDE the polygon area), ellipses (characterised by 3 points, but can contain more points on the edge), etc.

For example, how do I represent a polygon? Is it a weak entity? Can it have two relations (one for the characterisation and one for the content) ?

Here's an extract what I have right now :

I added the id identifiers because... Else there would be nothing inside my tables (which is bad I think).

So I am wondering if these entities should be weak, as they are identified by a set of identifiers of another entity? Can they have no attributes? And is it okay to have those two relations like so for each entity?

I guess what I would like to do is something like Ellipse(focalPoint1, focalPoint2, characterPoint) (3-tuple as compound key) and Has (label, focalPoint1, focalPoint2, characterPoint), but I do not know how to represent this.