summon: define yaml file schema

dvc/api.py

@@ -2,6 +2,7 @@ import importlib
 import os
 import sys
 from contextlib import contextmanager
+from voluptuous import Schema
 
 
 try:
@@ -16,6 +17,26 @@ from dvc.repo import Repo
 from dvc.external_repo import external_repo
 
 
+summon_schema = Schema(
+    {
+        "objects": [
+            {
+                "name": str,
+                "description": str,
+                "paper": str,
+                "metrics": dict,
+                "summon": {
+                    "type": "python",
+                    "call": str,
+                    "args": dict,
+                    "deps": [str]
+                },
+            }
+        ],
+    }
+)
+
+
 def get_url(path, repo=None, rev=None, remote=None):
     """Returns an url of a resource specified by path in repo"""
     with _make_repo(repo, rev=rev) as _repo: