3 files changed, 143 insertions, 0 deletions
diff --git a/bsfs/graph/ac/__init__.py b/bsfs/graph/ac/__init__.py
new file mode 100644
index 0000000..420de01
--- /dev/null
+++ b/bsfs/graph/ac/__init__.py
@@ -0,0 +1,20 @@
+"""
+
+Part of the BlackStar filesystem (bsfs) module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# imports
+import typing
+
+# inner-module imports
+from .base import AccessControlBase
+from .null import NullAC
+
+# exports
+__all__: typing.Sequence[str] = (
+    'AccessControlBase',
+    'NullAC',
+    )
+
+## EOF ##
diff --git a/bsfs/graph/ac/base.py b/bsfs/graph/ac/base.py
new file mode 100644
index 0000000..bc9aeb3
--- /dev/null
+++ b/bsfs/graph/ac/base.py
@@ -0,0 +1,71 @@
+"""
+
+Part of the BlackStar filesystem (bsfs) module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# imports
+import abc
+import typing
+
+# bsfs imports
+from bsfs import schema
+from bsfs.triple_store import TripleStoreBase
+from bsfs.utils import URI
+
+# exports
+__all__: typing.Sequence[str] = (
+    'AccessControlBase',
+    )
+
+
+## code ##
+
+class AccessControlBase(abc.ABC):
+    """Defines the interface for access control policies.
+
+    An access control policy governs which actions a user may take to query
+    or to manipulate a graph.
+
+    """
+
+    # The triple store backend.
+    _backend: TripleStoreBase
+
+    # The current user.
+    _user: URI
+
+    def __init__(
+            self,
+            backend: TripleStoreBase,
+            user: URI,
+            ):
+        self._backend = backend
+        self._user = URI(user)
+
+    @abc.abstractmethod
+    def is_protected_predicate(self, pred: schema.Predicate) -> bool:
+        """Return True if a predicate cannot be modified manually."""
+
+    @abc.abstractmethod
+    def create(self, node_type: schema.Node, guids: typing.Iterable[URI]):
+        """Perform post-creation operations on nodes, e.g. ownership information."""
+
+    @abc.abstractmethod
+    def link_from_node(self, node_type: schema.Node, guids: typing.Iterable[URI]) -> typing.Iterable[URI]:
+        """Return nodes for which outbound links can be written."""
+
+    @abc.abstractmethod
+    def link_to_node(self, node_type: schema.Node, guids: typing.Iterable[URI]) -> typing.Iterable[URI]:
+        """Return nodes for which inbound links can be written."""
+
+    @abc.abstractmethod
+    def write_literal(self, node_type: schema.Node, guids: typing.Iterable[URI]) -> typing.Iterable[URI]:
+        """Return nodes to which literals can be attached."""
+
+    @abc.abstractmethod
+    def createable(self, node_type: schema.Node, guids: typing.Iterable[URI]) -> typing.Iterable[URI]:
+        """Return nodes that are allowed to be created."""
+
+
+## EOF ##
diff --git a/bsfs/graph/ac/null.py b/bsfs/graph/ac/null.py
new file mode 100644
index 0000000..36838bd
--- /dev/null
+++ b/bsfs/graph/ac/null.py
@@ -0,0 +1,52 @@
+"""
+
+Part of the BlackStar filesystem (bsfs) module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# imports
+import typing
+
+# bsfs imports
+from bsfs import schema
+from bsfs.namespace import ns
+from bsfs.utils import URI
+
+# inner-module imports
+from . import base
+
+# exports
+__all__: typing.Sequence[str] = (
+    'NullAC',
+    )
+
+
+## code ##
+
+class NullAC(base.AccessControlBase):
+    """The NULL access control implements a dummy policy that allows any action to any user."""
+
+    def is_protected_predicate(self, pred: schema.Predicate) -> bool:
+        """Return True if a predicate cannot be modified manually."""
+        return pred.uri == ns.bsm.t_created
+
+    def create(self, node_type: schema.Node, guids: typing.Iterable[URI]):
+        """Perform post-creation operations on nodes, e.g. ownership information."""
+
+    def link_from_node(self, node_type: schema.Node, guids: typing.Iterable[URI]) -> typing.Iterable[URI]:
+        """Return nodes for which outbound links can be written."""
+        return guids
+
+    def link_to_node(self, node_type: schema.Node, guids: typing.Iterable[URI]) -> typing.Iterable[URI]:
+        """Return nodes for which inbound links can be written."""
+        return guids
+
+    def write_literal(self, node_type: schema.Node, guids: typing.Iterable[URI]) -> typing.Iterable[URI]:
+        """Return nodes to which literals can be attached."""
+        return guids
+
+    def createable(self, node_type: schema.Node, guids: typing.Iterable[URI]) -> typing.Iterable[URI]:
+        """Return nodes that are allowed to be created."""
+        return guids
+
+## EOF ##