How to create multiple 'aggregate' facts on a 'parent' object calculated from child objects (composition)

I have object(s) that will introduce facts that also have 'child' objects (composition). There will be multiple facts that are aggregate values on the parent that are calculated from the 'children.'

Typically these aggregate fact on the parent will follow one of the following patterns:

- count of children matching a filter (or all)
- sum of children matching a filter (or all)

I didn't see anything like that in the examples. It would be great if it could be added!

首先檢視 repository 中現有的範例，以及此處列出的需求：根據組合後的子項計算父層 facts，包括經過篩選或未經篩選的計數與總和。確認規則引擎是否已支援此模式；要視為完成，必須提供一個具體範例，或一份範圍明確的實作提案，用來定義所支援的彙總行為。

由索引模型根據 Issue 內容生成。