# Dictionary of user-facing values
<a name="feature-overview-storage-dictionary"></a>

Neptune does not store most user-facing values directly in the various indexes it maintains. Instead, it stores them separately in a dictionary and replaces them in the indexes with 8-byte identifiers.
+ All user-facing values that would go in `S`, `P`, or `G` indexes are stored in the dictionary in this way.
+ In the `O` index, numeric values are stored directly in the index (inlined). This includes `date` and `datetime` values (represented as milliseconds from the epoch).
+ All other user-facing values that would go in the `O` index are stored in the dictionary and represented in the index by IDs.

The dictionary contains a forward mapping of user-facing values to 8-byte IDs in a `value_to_id` index.

It stores the reverse mapping of 8-byte IDs to values in one of two indexes, depending on the size of the values:
+ An `id_to_value` index maps IDs to user-facing values that are smaller than 767 bytes after internal encoding.
+ An `id_to_blob` index maps IDs to user-facing values that are larger.