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diff --git a/bsie/base/reader.py b/bsie/base/reader.py
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+"""The Reader classes return high-level content structures from files.
+
+The Reader fulfills two purposes:
+    First, it brokers between multiple libraries and file formats.
+    Second, it separates multiple aspects of a file into distinct content types.
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# imports
+import abc
+import typing
+
+# inner-module imports
+from bsie.utils.bsfs import URI, typename
+
+# exports
+__all__: typing.Sequence[str] = (
+    'Aggregator',
+    'Reader',
+    )
+
+
+## code ##
+
+class Reader(abc.ABC):
+    """Read and return some content from a file."""
+
+    # In what data structure content is returned
+    CONTENT_TYPE = typing.Union[typing.Any]
+    # NOTE: Child classes must also assign a typing.Union even if there's
+    # only one options
+
+    def __str__(self) -> str:
+        return typename(self)
+
+    def __repr__(self) -> str:
+        return f'{typename(self)}()'
+
+    # FIXME: How about using contexts instead of calls?
+    @abc.abstractmethod
+    def __call__(self, path: URI) -> CONTENT_TYPE:
+        """Return some content of the file at *path*.
+        Raises a `ReaderError` if the reader cannot make sense of the file format.
+        """
+
+## EOF ##