diff --git a/extensions/linz/notebooks/asset-datetime-summary.ipynb b/extensions/linz/notebooks/asset-datetime-summary.ipynb
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+++ b/extensions/linz/notebooks/asset-datetime-summary.ipynb
@@ -0,0 +1,495 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "4b29124d-9e52-4124-8b9f-efb60762c0dc",
+   "metadata": {},
+   "source": [
+    "# Creating asset summaries"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "d38f9eb9-e10e-4903-9772-8b887e3cdef5",
+   "metadata": {},
+   "source": [
+    "We'll need a *LINZ extension schema validator:*"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "id": "7b2d67c6-3313-4023-9752-49d133d86d59",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from json import dumps, load\n",
+    "from sys import stderr\n",
+    "from urllib.request import urlopen\n",
+    "\n",
+    "from IPython.display import JSON\n",
+    "from jsonschema import Draft7Validator\n",
+    "\n",
+    "with urlopen(\"https://stac.linz.govt.nz/v0.0.10/linz/schema.json\") as schema_pointer:\n",
+    "    schema = load(schema_pointer)\n",
+    "\n",
+    "validator = Draft7Validator(schema)\n",
+    "\n",
+    "def validate(instance: str) -> None:\n",
+    "    found_error = False\n",
+    "    \n",
+    "    for error in validator.iter_errors(instance):\n",
+    "        found_error = True\n",
+    "        print(error.message, file=stderr)\n",
+    "    \n",
+    "    if not found_error:\n",
+    "        print(\"Validated successfully\")\n",
+    "        "
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "5e32302e-6714-494f-bbe0-23a60d9b383e",
+   "metadata": {
+    "tags": []
+   },
+   "source": [
+    "The *collection example* is valid:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "id": "3931b743-885d-47ec-aff4-48faa8c6da5b",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Validated successfully\n"
+     ]
+    }
+   ],
+   "source": [
+    "with urlopen(\"https://stac.linz.govt.nz/v0.0.10/linz/examples/collection.json\") as example_pointer:\n",
+    "    example = load(example_pointer)\n",
+    "\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "f0e21a05-f00f-4923-a457-b3a7f25907d8",
+   "metadata": {},
+   "source": [
+    "Can we *summarise assets?*"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "76ec8b0b-6d5a-4902-a0b1-6b1415b577f3",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Validated successfully\n"
+     ]
+    }
+   ],
+   "source": [
+    "example[\"summaries\"][\"assets\"] = {\n",
+    "    \"created\": {\"minimum\": \"1999-01-01T00:00:00Z\", \"maximum\": \"2010-01-01T00:00:00Z\"},\n",
+    "    \"updated\": {\"minimum\": \"1999-01-02T00:00:00Z\", \"maximum\": \"2010-01-02T00:00:00Z\"},\n",
+    "}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "3cb90d1c-d25f-46e5-9885-c3d4f303ef09",
+   "metadata": {},
+   "source": [
+    "Yes, but *are such properties validated as normal summaries?*"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "id": "2f043e5c-11a9-4ad8-9d6b-4ce8fe4cb1c0",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Validated successfully\n"
+     ]
+    }
+   ],
+   "source": [
+    "example[\"summaries\"][\"assets\"] = {\n",
+    "    \"created\": None,\n",
+    "    \"updated\": {\"minimum\": \"1999-01-02T00:00:00Z\"},\n",
+    "}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "16355abb-5da3-4486-9ae7-4f450330c508",
+   "metadata": {},
+   "source": [
+    "Oops, that should've caused *validation exceptions!* Let's instead extend the schema to validate asset summaries as normal summaries:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "id": "4cd36c8b-ac96-4ea3-a4a2-0db92ef07675",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "None is not valid under any of the given schemas\n",
+      "{'minimum': '1999-01-02T00:00:00Z'} is not valid under any of the given schemas\n"
+     ]
+    }
+   ],
+   "source": [
+    "summaries_schema = schema[\"definitions\"][\"fields\"][\"properties\"][\"summaries\"]\n",
+    "summaries_schema[\"properties\"][\"assets\"] = {\n",
+    "    \"additionalProperties\": {\n",
+    "        \"$ref\": \"https://schemas.stacspec.org/v1.0.0/collection-spec/json-schema/collection.json#definitions/summaries/additionalProperties\"\n",
+    "    }\n",
+    "}\n",
+    "\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "58b70eb6-84cb-4eda-813f-1508a2cbe1a6",
+   "metadata": {},
+   "source": [
+    "Looks like that worked. For the LINZ schema we want to be even stricter. Let's start by requiring the `assets` property:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 6,
+   "id": "84ad9bf2-b324-47c4-a453-431bc2fcc8a9",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "'assets' is a required property\n"
+     ]
+    }
+   ],
+   "source": [
+    "summaries_schema[\"required\"] = summaries_schema.get(\"required\", []) + [\"assets\"]\n",
+    "\n",
+    "del example[\"summaries\"][\"assets\"]\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "7741d37b-1a1b-4999-afe2-6b65a6c306a4",
+   "metadata": {},
+   "source": [
+    "Good! We also want to require `created` and `updated`:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 7,
+   "id": "0c75c673-7894-47f4-8712-46451488bb87",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "'created' is a required property\n",
+      "'updated' is a required property\n",
+      "{'stac_version': '1.0.0', 'stac_extensions': ['https://linz.github.io/stac/v0.0.10/linz/schema.json', 'https://linz.github.io/stac/v0.0.10/quality/schema.json', 'https://stac-extensions.github.io/file/v2.0.0/schema.json', 'https://stac-extensions.github.io/projection/v1.0.0/schema.json', 'https://stac-extensions.github.io/version/v1.0.0/schema.json'], 'type': 'Collection', 'id': 'collection', 'title': 'A title', 'description': 'A description', 'license': 'Apache-2.0', 'linz:lifecycle': 'under development', 'linz:providers': [{'name': 'Example', 'description': 'Example description.', 'roles': ['custodian'], 'url': 'https://www.exampleurl.com'}, {'name': 'Example', 'description': 'Example description.', 'roles': ['manager'], 'url': 'https://www.exampleurl.com'}], 'linz:security_classification': 'unclassified', 'extent': {'spatial': {'bbox': [[172.9, 1.3, 173, 1.4]]}, 'temporal': {'interval': [['2015-06-23T00:00:00Z', None]]}}, 'summaries': {'created': {'minimum': '1999-01-01T00:00:00Z', 'maximum': '2010-01-01T00:00:00Z'}, 'updated': {'minimum': '1999-01-02T00:00:00Z', 'maximum': '2010-01-02T00:00:00Z'}, 'datetime': {'minimum': '2015-06-23T00:00:00Z', 'maximum': '2019-07-10T13:44:56Z'}, 'linz:geospatial_type': ['polygon'], 'assets': {}}, 'links': [], 'quality:description': 'Example quality description', 'quality:horizontal_accuracy': 1, 'quality:horizontal_accuracy_type': 'nominal', 'linz:history': 'This is an example dataset lineage description.', 'providers': [{'name': 'Example', 'description': 'Example description.', 'roles': ['licensor'], 'url': 'https://www.exampleurl.com'}, {'name': 'Example', 'description': 'Example description.', 'roles': ['producer'], 'url': 'https://www.exampleurl.com'}], 'version': '2.0.0', 'assets': {'example': {'href': 'https://example.com/examples/file.xyz', 'created': '2000-01-01T00:00:00Z', 'updated': '2020-01-01T00:00:00Z', 'file:checksum': '1220e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855', 'proj:epsg': 32659}}} is not valid under any of the given schemas\n"
+     ]
+    }
+   ],
+   "source": [
+    "summaries_schema[\"properties\"][\"assets\"][\"required\"] = [\"created\", \"updated\"]\n",
+    "\n",
+    "example[\"summaries\"][\"assets\"] = {}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "ec1eac97-716a-4aac-8ebe-a19ea67766ba",
+   "metadata": {},
+   "source": [
+    "Finally we want to make sure `minimum` and `maximum` are datetimes. At this point we've basically reimplemented `summaries/additionalProperties`, so we can delete that:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "b584a70d-5c29-45a5-a6a4-337e844cfddf",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stderr",
+     "output_type": "stream",
+     "text": [
+      "'created minimum' does not match '(\\\\+00:00|Z)$'\n",
+      "'created maximum' does not match '(\\\\+00:00|Z)$'\n",
+      "'updated minimum' does not match '(\\\\+00:00|Z)$'\n",
+      "'updated maximum' does not match '(\\\\+00:00|Z)$'\n"
+     ]
+    }
+   ],
+   "source": [
+    "summaries_schema[\"properties\"][\"assets\"].pop(\"additionalProperties\", None)\n",
+    "summaries_schema[\"properties\"][\"assets\"][\"properties\"] = {\n",
+    "    \"created\": {\n",
+    "        \"type\": \"object\",\n",
+    "        \"required\": [\"minimum\", \"maximum\"],\n",
+    "        \"properties\": {\n",
+    "            \"minimum\": {\n",
+    "                \"type\": \"string\",\n",
+    "                \"format\": \"date-time\",\n",
+    "                \"pattern\": \"(\\\\+00:00|Z)$\"\n",
+    "            },\n",
+    "            \"maximum\": {\n",
+    "                \"type\": \"string\",\n",
+    "                \"format\": \"date-time\",\n",
+    "                \"pattern\": \"(\\\\+00:00|Z)$\"\n",
+    "            }\n",
+    "        }\n",
+    "    },\n",
+    "    \"updated\": {\n",
+    "        \"type\": \"object\",\n",
+    "        \"required\": [\"minimum\", \"maximum\"],\n",
+    "        \"properties\": {\n",
+    "            \"minimum\": {\n",
+    "                \"type\": \"string\",\n",
+    "                \"format\": \"date-time\",\n",
+    "                \"pattern\": \"(\\\\+00:00|Z)$\"\n",
+    "            },\n",
+    "            \"maximum\": {\n",
+    "                \"type\": \"string\",\n",
+    "                \"format\": \"date-time\",\n",
+    "                \"pattern\": \"(\\\\+00:00|Z)$\"\n",
+    "            }\n",
+    "        }\n",
+    "    }\n",
+    "}\n",
+    "\n",
+    "example[\"summaries\"][\"assets\"] = {\n",
+    "    \"created\": {\"minimum\": \"created minimum\", \"maximum\": \"created maximum\"},\n",
+    "    \"updated\": {\"minimum\": \"updated minimum\", \"maximum\": \"updated maximum\"}\n",
+    "}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "04934fbc-8482-43fe-9991-1e6bfdf04737",
+   "metadata": {},
+   "source": [
+    "Let's make sure by reverting to the valid summary:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "id": "8e7cfdb5-1232-40fd-957b-9b01f7448401",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Validated successfully\n"
+     ]
+    }
+   ],
+   "source": [
+    "example[\"summaries\"][\"assets\"] = {\n",
+    "    \"created\": {\"minimum\": \"1999-01-01T00:00:00Z\", \"maximum\": \"2010-01-01T00:00:00Z\"},\n",
+    "    \"updated\": {\"minimum\": \"1999-01-02T00:00:00Z\", \"maximum\": \"2010-01-02T00:00:00Z\"},\n",
+    "}\n",
+    "validate(example)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "6ee3378f-5507-4831-8611-ce56c52304ac",
+   "metadata": {},
+   "source": [
+    "And we're golden! The final summaries schema looks like this:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "id": "f05ddf06-3d64-4c4f-a03b-80c4643f61ae",
+   "metadata": {},
+   "outputs": [
+    {
+     "data": {
+      "application/json": {
+       "properties": {
+        "assets": {
+         "properties": {
+          "created": {
+           "properties": {
+            "maximum": {
+             "format": "date-time",
+             "pattern": "(\\+00:00|Z)$",
+             "type": "string"
+            },
+            "minimum": {
+             "format": "date-time",
+             "pattern": "(\\+00:00|Z)$",
+             "type": "string"
+            }
+           },
+           "required": [
+            "minimum",
+            "maximum"
+           ],
+           "type": "object"
+          },
+          "updated": {
+           "properties": {
+            "maximum": {
+             "format": "date-time",
+             "pattern": "(\\+00:00|Z)$",
+             "type": "string"
+            },
+            "minimum": {
+             "format": "date-time",
+             "pattern": "(\\+00:00|Z)$",
+             "type": "string"
+            }
+           },
+           "required": [
+            "minimum",
+            "maximum"
+           ],
+           "type": "object"
+          }
+         },
+         "required": [
+          "created",
+          "updated"
+         ]
+        },
+        "created": {
+         "properties": {
+          "maximum": {
+           "format": "date-time",
+           "pattern": "(\\+00:00|Z)$",
+           "title": "Latest asset creation time",
+           "type": "string"
+          },
+          "minimum": {
+           "format": "date-time",
+           "pattern": "(\\+00:00|Z)$",
+           "title": "Earliest asset creation time",
+           "type": "string"
+          }
+         },
+         "required": [
+          "minimum",
+          "maximum"
+         ],
+         "type": "object"
+        },
+        "linz:geospatial_type": {
+         "items": {
+          "$ref": "#/definitions/geospatial_type_enum"
+         },
+         "type": "array"
+        },
+        "updated": {
+         "properties": {
+          "maximum": {
+           "format": "date-time",
+           "pattern": "(\\+00:00|Z)$",
+           "title": "Latest asset updated time",
+           "type": "string"
+          },
+          "minimum": {
+           "format": "date-time",
+           "pattern": "(\\+00:00|Z)$",
+           "title": "Earliest asset updated time",
+           "type": "string"
+          }
+         },
+         "required": [
+          "minimum",
+          "maximum"
+         ],
+         "type": "object"
+        }
+       },
+       "required": [
+        "created",
+        "updated",
+        "linz:geospatial_type",
+        "assets"
+       ],
+       "type": "object"
+      },
+      "text/plain": [
+       "<IPython.core.display.JSON object>"
+      ]
+     },
+     "execution_count": 10,
+     "metadata": {
+      "application/json": {
+       "expanded": false,
+       "root": "root"
+      }
+     },
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "JSON(summaries_schema)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python3 - stac",
+   "language": "python",
+   "name": "ipython_stac"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.8.9"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}