I am going through some code base(big project) and and i saw the code to create schema in schema directory

  def register_fcm_schema() do
    %{
      type: "object",
      schema: %{
        user_id: %{
          type: "int_or_string",
          required: true
        },
        device_id: %{
          type: "string",
          required: true
        },
        fcm_token: %{
          type: "string",
          required: true
        }
      }
    }
  end

and in ecto module i saw different definition

defmodule Friends.Person do
  use Ecto.Schema

  schema "people" do
    field :name, :string
    field :age, :integer, default: 0
  end
end

help me out to understand what is the meaning of first code -->( def register_fcm_schema() )??
what exectly it trying to define?? and how many way we can create schema??