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diff --git a/bsfs/triple_store/base.py b/bsfs/triple_store/base.py
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+"""
+
+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
+
+# inner-module imports
+from bsfs.utils import URI, typename
+import bsfs.schema  as _schema
+
+# exports
+__all__: typing.Sequence[str] = (
+    'TripleStoreBase',
+    )
+
+
+## code ##
+
+class TripleStoreBase(abc.ABC):
+    """
+    """
+
+    # storage's URI. None implies a temporary location.
+    uri: typing.Optional[URI] = None
+
+    def __init__(self, uri: typing.Optional[URI] = None):
+        self.uri = uri
+
+    def __hash__(self) -> int:
+        uri = self.uri if self.uri is not None else id(self)
+        return hash((type(self), uri))
+
+    def __eq__(self, other) -> bool:
+        return isinstance(other, type(self)) \
+           and (( self.uri is not None \
+           and    other.uri is not None \
+           and    self.uri == other.uri ) \
+            or  id(self) == id(other))
+
+    def __repr__(self) -> str:
+        return f'{typename(self)}(uri={self.uri})'
+
+    def __str__(self) -> str:
+        return f'{typename(self)}(uri={self.uri})'
+
+    def is_persistent(self) -> bool:
+        """Return True if data is stored persistently."""
+        return self.uri is not None
+
+
+    @classmethod
+    @abc.abstractmethod
+    def Open(
+            cls,
+            uri: str,
+            **kwargs: typing.Any,
+            ) -> 'TripleStoreBase':
+        """Return a TripleStoreBase instance connected to *uri*."""
+
+    @abc.abstractmethod
+    def commit(self):
+        """Commit the current transaction."""
+
+    @abc.abstractmethod
+    def rollback(self):
+        """Undo changes since the last commit."""
+
+    @property
+    @abc.abstractmethod
+    def schema(self) -> _schema.Schema:
+        """Return the store's local schema."""
+
+    @schema.setter
+    def schema(self, schema: _schema.Schema):
+        """Migrate to new schema by adding or removing class definitions.
+
+        Commits before and after the migration.
+
+        Instances of removed classes will be deleted irreversably.
+        Note that modifying an existing class is not directly supported.
+        Also, it is generally discouraged, since changing definitions may
+        lead to inconsistencies across multiple clients in a distributed
+        setting. Instead, consider introducing a new class under its own
+        uri. Such a migration would look as follows:
+
+        1. Add new class definitions.
+        2. Create instances of the new classes and copy relevant data.
+        3. Remove the old definitions.
+
+        To modify a class, i.e., re-use a previous uri with a new
+        class definition, you would have to migrate via temporary
+        class definitions, and thus repeat the above procedure two times.
+
+        """
+
+    @abc.abstractmethod
+    def exists(
+            self,
+            node_type: _schema.Node,
+            guids: typing.Iterable[URI],
+            ):
+        """
+        """
+
+    @abc.abstractmethod
+    def create(
+            self,
+            node_type: _schema.Node,
+            guids: typing.Iterable[URI],
+            ):
+        """Create *guid* nodes with type *subject*."""
+
+    @abc.abstractmethod
+    def set(
+            self,
+            node_type: _schema.Node, # FIXME: is the node_type even needed? Couldn't I infer from the predicate?
+            guids: typing.Iterable[URI],
+            predicate: _schema.Predicate,
+            values: typing.Iterable[typing.Any],
+            ):
+        """
+        """
+
+## EOF ##