Fix up column names.

src/schema/objects/columns.yaml

@@ -110,6 +110,13 @@ derived_from:
     for example a slice of tissue (`sample-02`) derived from a block of tissue (`sample-01`).
   type: string
   pattern: ^sample-[0-9a-zA-Z]+$
+desc_id:
+  name: desc_id
+  display_name: Description Label
+  description: |
+    A `desc-<label>` entity present in the derivatives dataset.
+  type: string
+  pattern: ^desc-[0-9a-zA-Z]+$
 description:
   name: description
   display_name: Description
@@ -122,6 +129,12 @@ description__optode:
   description: |
     Free-form text description of the optode, or other information of interest.
   type: string
+description__descriptions:
+  name: description
+  display_name: Description
+  description: |
+    Free-form text description of the desc entity's label (defined in `desc_id`).
+  type: string
 dimension:
   name: dimension
   display_name: Dimension

src/schema/rules/tabular_data/derivatives/common_derivatives.yaml

@@ -16,6 +16,6 @@ Descriptions:
     - path == "descriptions.tsv"
   columns:
     desc_id: required
-    description: required
-  index_columns: [desc_id, description]
+    description__descriptions: required
+  index_columns: [desc_id]
   additional_columns: allowed