fix requirement of mlm:model role, required only by at least one asset

CHANGELOG.md

@@ -20,7 +20,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - n/a
 
 ### Fixed
-- n/a
+- Fix the validation strategy of the `mlm:model` role required by at least one Asset under a STAC Item.
+  Although the role requirement was validated, the definition did not allow for other Assets without it to exist.
 
 ## [v1.1.0](https://github.com/crim-ca/mlm-extension/tree/v1.1.0)
 

json-schema/schema.json

@@ -8,6 +8,7 @@
       "$comment": "This is the schema for STAC extension MLM in Items.",
       "allOf": [
         {
+          "$comment": "Schema to validate the MLM fields under Item properties or Assets properties.",
           "type": "object",
           "required": [
             "type",
@@ -40,10 +41,6 @@
                 "allOf": [
                   {
                     "$ref": "#/$defs/fields"
-                  },
-                  {
-                    "$comment": "At least one Asset must provide the model definition.",
-                    "$ref": "#/$defs/AssetModelRole"
                   }
                 ]
               }
@@ -52,6 +49,10 @@
         },
         {
           "$ref": "#/$defs/stac_extensions_mlm"
+        },
+        {
+          "$comment": "Schema to validate model role requirement.",
+          "$ref": "#/$defs/AssetModelRoleMinimumOneDefinition"
         }
       ]
     },
@@ -646,6 +647,52 @@
     "DataType": {
       "$ref": "https://stac-extensions.github.io/raster/v1.1.0/schema.json#/definitions/bands/items/properties/data_type"
     },
+    "AssetModelRoleMinimumOneDefinition": {
+      "$comment": "At least one Asset must provide the model definition indicated by the 'mlm:model' role.",
+      "required": [
+        "assets"
+      ],
+      "anyOf": [
+        {
+          "properties": {
+            "assets": {
+              "additionalProperties": {
+                "properties": {
+                  "roles": {
+                    "type": "array",
+                    "items": {
+                      "const": "mlm:model"
+                    },
+                    "minItems": 1
+                  }
+                }
+              }
+            }
+          }
+        },
+        {
+          "not": {
+            "properties": {
+              "assets": {
+                "additionalProperties": {
+                  "properties": {
+                    "roles": {
+                      "type": "array",
+                      "items": {
+                        "type": "string",
+                        "not": {
+                          "const": "mlm:model"
+                        }
+                      }
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      ]
+    },
     "AssetModelRole": {
       "required": ["roles"],
       "properties": {

tests/test_schema.py

@@ -66,6 +66,61 @@ def test_mlm_no_input_allowed_but_explicit_empty_array_required(
         pystac.validation.validate(mlm_item, validator=mlm_validator)
 
 
+@pytest.mark.parametrize(
+    "mlm_example",
+    ["item_basic.json"],
+    indirect=True,
+)
+def test_mlm_other_non_mlm_assets_allowed(
+    mlm_validator: STACValidator,
+    mlm_example: Dict[str, JSON],
+) -> None:
+    mlm_data = copy.deepcopy(mlm_example)
+    mlm_item = pystac.Item.from_dict(mlm_data)
+    pystac.validation.validate(mlm_item, validator=mlm_validator)  # self-check valid beforehand
+
+    mlm_data["assets"]["sample"] = {
+        "type": "image/jpeg",
+        "href": "https://example.com/sample/output.jpg",
+        "roles": ["preview"],
+        "title": "Model Output Predictions Sample",
+    }
+    mlm_data["assets"]["model-cart"] = {
+        "type": "text/markdown",
+        "href": "https://example.com/sample/model.md",
+        "roles": ["metadata"],
+        "title": "Model Cart",
+    }
+    mlm_item = pystac.Item.from_dict(mlm_data)
+    pystac.validation.validate(mlm_item, validator=mlm_validator)  # still valid
+
+
+@pytest.mark.parametrize(
+    "mlm_example",
+    ["item_basic.json"],
+    indirect=True,
+)
+def test_mlm_at_least_one_asset_model(
+    mlm_validator: STACValidator,
+    mlm_example: Dict[str, JSON],
+) -> None:
+    mlm_data = copy.deepcopy(mlm_example)
+    mlm_item = pystac.Item.from_dict(mlm_data)
+    pystac.validation.validate(mlm_item, validator=mlm_validator)  # self-check valid beforehand
+
+    mlm_data["assets"] = {  # needs at least 1 asset with role 'mlm:model'
+        "model": {
+            "type": "application/octet-stream; application=pytorch",
+            "href": "https://example.com/sample/checkpoint.pt",
+            "roles": ["checkpoint"],
+            "title": "Model Weights Checkpoint",
+        }
+    }
+    with pytest.raises(pystac.errors.STACValidationError):
+        mlm_item = pystac.Item.from_dict(mlm_data)
+        pystac.validation.validate(mlm_item, validator=mlm_validator)
+
+
 def test_model_metadata_to_dict(eurosat_resnet):
     assert eurosat_resnet.item.to_dict()