{
  "$schema": "http://json-schema.org/draft/2020-12/schema",
  "title": "Object Model",
  "type": "object",
  "properties": {
    "entities": {
      "type": "array",
      "items": { "$ref": "#/$defs/entity" }
    },
    "relationships": {
      "type": "array",
      "items": { "$ref": "#/$defs/relationship" }
    }
  },
  "required": ["entities"],

  "$defs": {
    "entity": {
      "type": "object",
      "properties": {
        "id": { "type": "string" },
        "name": { "type": "string" },
        "fields": {
          "type": "array",
          "items": { "$ref": "#/$defs/field" }
        },
        "methods": {
          "type": "array",
          "items": { "$ref": "#/$defs/method" }
        },
        "extensions": {
          "type": "object",
          "description": "Optional tool-specific metadata, e.g. graphical layout, color, notes"
        }
      },
      "required": ["id", "name"]
    },

    "field": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "type": { "type": "string" },
        "multiplicity": { "type": "string", "description": "e.g., 1, 0..1, 0..*, 1..*" },
        "visibility": { "enum": ["public", "private", "protected", "package"] },
        "default": {}
      },
      "required": ["name", "type"]
    },

    "method": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "parameters": {
          "type": "array",
          "items": { "$ref": "#/$defs/field" }
        },
        "returnType": { "type": "string" },
        "visibility": { "enum": ["public", "private", "protected", "package"] }
      },
      "required": ["name"]
    },

    "relationship": {
      "type": "object",
      "properties": {
        "type": { "enum": ["association", "aggregation", "composition", "inheritance"] },
        "source": { "type": "string", "description": "entity id" },
        "target": { "type": "string", "description": "entity id" },
        "multiplicity": { "type": "string", "description": "source..target multiplicity" },
        "extensions": {
          "type": "object",
          "description": "Optional metadata (e.g., graphical line style, arrow type, color)"
        }
      },
      "required": ["type", "source", "target"]
    }
  }
}