docarray · samsja · Dec 6, 2022 · Nov 29, 2022 · Nov 29, 2022 · Dec 1, 2022
diff --git a/docarray/array/abstract_array.py b/docarray/array/abstract_array.py
@@ -1,12 +1,18 @@
 from abc import abstractmethod
-from typing import Iterable, Type
+from typing import TYPE_CHECKING, Dict, Iterable, List, Optional, Sequence, Type, Union
 
 from docarray.document import BaseDocument
 
+if TYPE_CHECKING:
+    from docarray.typing import NdArray, TorchTensor
 
-class AbstractDocumentArray(Iterable):
+
+class AbstractDocumentArray(Sequence):
 
     document_type: Type[BaseDocument]
+    _columns: Optional[
+        Dict[str, Union['TorchTensor', 'AbstractDocumentArray', 'NdArray', None]]
+    ]  # here columns are the holder of the data in tensor modes
 
     @abstractmethod
     def __init__(self, docs: Iterable[BaseDocument]):
@@ -17,3 +23,11 @@ def __class_getitem__(
         cls, item: Type[BaseDocument]
     ) -> Type['AbstractDocumentArray']:
         ...
+
+    @abstractmethod
+    def is_stacked(self) -> bool:
+        ...
+
+    @abstractmethod
+    def _column_fields(self) -> List[str]:
+        ...