Public UDM 统一数据模型

SIYB E 的核心数据模型：把 Measurement 作为中心节点，连接 Technology、Signal、Interface、Protocol、Algorithm、Formula、Model、Threshold、Standard、Paper、Dataset、Scenario、Product。

UDM 不是数据库表结构，而是知识图谱的语义层。它同时驱动网站内容组织、搜索、API 与 MCP 工具。

关系链：Measurement → measured_by Technology → outputs Signal → uses Interface → transported_by Protocol → processed_by Algorithm → derived_by Formula → feeds Model → evaluated_by Threshold → governed_by Standard → supported_by Paper → applied_to Scenario → available_as Product。

每条关系都可以带条件（conditions）与证据（evidence），例如"FDR 测土壤含水率"在"含石量高"条件下精度下降。

{
  "measurement": { "id": "snow-water-equivalent", "unit": "mm" },
  "measured_by": [
    { "technology": "snow-pillow", "conditions": "需平整地基", "accuracy": "±1~3%" },
    { "technology": "gamma-swe",  "conditions": "需扣除土壤水分基线", "accuracy": "±5~15 mm" }
  ],
  "derived_by":  { "formula": "swe-from-depth-density", "inputs": ["snow-depth","snow-density"] },
  "evaluated_by":[{ "threshold": "swe-flood-risk", "status": "待验证（经验值）" }],
  "governed_by": [{ "standard": "WMO-No.8" }, { "standard": "ISO-18320" }],
  "applied_to":  [{ "scenario": "alpine-snow" }],
  "available_as":[{ "product": "satelliteRtu" }]
}