Introduce a model of a Commit

This is intentionally a Git Term. The `DataladDatasetVersion` is just an
alias. We should be able to declare it that way.

src/examples/datalad-dataset.yaml

@@ -74,38 +74,29 @@ graph:
       outputs.txt:
         content: MD5E-s4--ba1f2511fc30423bdbb183fe33f3dd0f.txt
         type: file
-        #  # annotate availability of the entire tree
-        #  available_at:
-        #    # map storage to storage-specific identifier
-        #    # here the "remote" identifier is the same as for the tree, because
-        #    # the storage is a clone of the repo
-        #    - access: 27f0483a-8c70-11ee-b9d6-3b5dd1955fcc
-        #    # the whole directory also exists as a copy in a remote zipfile
-        #    # the zipfile only contains this directory
-        #    - access: 6860c9e8-8c76-11ee-8f18-bb3625743f23
-        #      storage_id: .
-        #
-        ## particular dataset version
-        #- id: 7726424f50c6e9a70ba31e8d44c5d86fc46170da
-        #  type: commit
-        #  # entrypoint to the content
-        #  content: fb715e5f3c368ae50cf16c9b6a8e5ca23a353ea4
-        #  # some other metadata
-        #  # the next too could be instances of an `Agent`
-        #  author:
-        #    - name: Michael Hanke
-        #    - email: [email protected]
-        #  creator:
-        #    - name: Michael Hanke
-        #    - email: [email protected]
-        #  # ISO timestamp
-        #  created: 2023-11-25T12:04:53+01:00
-        #  # commit subject
-        #  title: Initial commit
-        #  # commit message body
-        #  description: Something elaborate, as usual
-        #  # previous versions
-        #  parent_commits:
+
+  # particular dataset version
+  - id: 7726424f50c6e9a70ba31e8d44c5d86fc46170da
+    objtype: Commit
+    # entrypoint to the content
+    tree: fb715e5f3c368ae50cf16c9b6a8e5ca23a353ea4
+    # some other metadata
+    # the next too could be instances of an `Agent`
+    author:
+      name: Michael Hanke
+      email: [email protected]
+    committer:
+      name: Michael Hanke
+      email: [email protected]
+    # ISO timestamp
+    created: 2023-11-25T12:04:53+01:00
+    # commit subject
+    title: Initial commit
+    # commit message body
+    description: Something elaborate, as usual
+    # previous versions
+    # TODO we need the parent commits to have sortable versions
+    #parent_commits:
 
   # object access methods
   # they can be rather heterogeneous, different parameters, etc

src/linkml/datalad-datasets.yaml

@@ -4,6 +4,7 @@ id: https://concepts.datalad.org/datalad-datasets
 name: datalad-datasets
 prefixes:
   dlco: https://concepts.datalad.org/
+  dct: http://purl.org/dc/terms/
 imports:
   - datasets
   - types
@@ -168,6 +169,44 @@ classes:
           - range: Directory
           # TODO: commit/dataset
 
+  Commit:
+    is_a: TypedThing
+    mixins:
+      - IdentifiedThing
+    attributes:
+      tree:
+        # we want content to come in separate, identified records, always.
+        # this enables referencing across multiple containers (versions,
+        # datasets).
+        inlined: false
+        description: >-
+          Tree referenced by the commit.
+        range: Directory
+      author:
+        slot_uri: dct:author
+        # TODO dedicated class for a GitAgent
+        range: GitAgent
+      committer:
+        slot_uri: dct:creator
+        range: GitAgent
+      created:
+        slot_uri: dct:created
+        # TODO ISO date type
+        range: string
+      title:
+        range: string
+      description:
+        range: string
+
+  GitAgent:
+    description: >-
+      Agent representation in a Git context
+    attributes:
+      name:
+        range: string
+      email:
+        # TODO email
+        range: string
 
 #  DataladDataset:
 #    is_a: Dataset