Referencing other entities

I apologise if it's just me, but by reading the docs it's not very clear how to reference other entities inside datascript.

``` clojure
[
 {:db/id -10
  :name "C1"
  :value "foo"} 
 {:db/id -11
  :name "C2"
  :value "bar"}      
 {:db/id -1
  :name  "E"
  :components [-10, -11]}
]
```

How do I reference the generated ids `10` and `11` inside the `components` vector?
