rok commented on code in PR #585:
URL: https://github.com/apache/parquet-format/pull/585#discussion_r3550802077
##########
LogicalTypes.md:
##########
@@ -635,7 +635,133 @@ The type has two type parameters:
The sort order used for `GEOGRAPHY` is undefined. When writing data, no min/max
statistics should be saved for this type and if such non-compliant statistics
-are found during reading, they must be ignored.
+are found during reading, they must be ignored.
+
+### FILE
+
+`FILE` annotates a group that represents a reference to a range of bytes,
which may
+be stored inline in the value, elsewhere within this file, or in an external
file. It
+is intended for use cases such as storing file inventories, manifests, and
unstructured
+data references (e.g., images or audio files stored in object storage).
+
+The annotated group may contain the following fields, identified by name.
Field IDs
+may also be used for projection. All fields are optional:
+
+| Field | Type | Required |
+|----------------|------------|----------|
+| `path` | STRING | No |
+| `offset` | INT64 | No |
+| `size` | INT64 | No |
+| `content_type` | STRING | No |
+| `checksum` | STRING | No |
+| `inline` | BYTE_ARRAY | No |
+
+A value resolves to bytes determined by `inline` / `path` / `offset` / `size`;
+`content_type` and `checksum` are metadata describing whatever is resolved.
+
+#### Fields
+
+##### path
+
+An opaque path string to an external file (e.g., `s3://bucket/file.jpg`). No
special
+encoding (e.g., URI encoding) is applied on top of the user provided data. If
`path` is absent,
+the value refers to this file (a self-reference).
+
+##### offset
+
+A byte offset indicating the start of the byte range within the referenced
data.
+If not provided, readers must treat the value as 0.
+If provided and non-zero, readers must seek to this offset to retrieve the
referenced data.
+
+##### size
+
+The byte length of the referenced data. Must be zero or a positive integer if
provided.
+A value of 0 indicates empty referenced data. If not provided, the range runs
to the end
+of the referenced data.
+
+##### content_type
+
+The media type (MIME type) of the resolved bytes (e.g., `image/png`).
+
+##### checksum
+
+A self-describing integrity token for the resolved bytes, of the form
+`<algorithm>:base64(<digest bytes>)`. It generalizes the storage-system eTag.
The
+recognized algorithms are:
+
+| Algorithm | Notes |
+|-----------|----------------------------------------------------------------|
+| `ETAG` | the object-store eTag — equality-only, not recomputable |
+| `MD5` | the usual S3/HTTP eTag and Content-MD5 |
+| `CRC32` | Parquet's page-checksum algorithm (gzip/zlib) |
+| `CRC32C` | common in object stores, hardware-accelerated |
+| `SHA-256` | e.g. S3 additional checksums |
+
+`checksum` applies to the resolved bytes, except for `ETAG`, which is the
+object-store eTag for the whole file referenced by `path`.
+
+##### inline
+
+The referenced bytes stored inline in the value. If `inline` is set, it
supplies the
+bytes and any locator fields (`path`, `offset`, `size`) that are present are
provenance
+only.
+
+#### Resolution
+
+A value resolves to bytes based on which of `inline`, `path`, `offset`, and
`size` are
+set:
+
+| `inline` | `path` | `offset` | `size` | Resolves to
|
+|----------|--------|----------|--------|----------------------------------------------|
+| set | – | – | – | the inline bytes
|
+| – | set | – | – | whole external file at `path`
|
+| – | set | set | – | external `path`, `[offset, EOF)`
|
+| – | set | – | set | external `path`, `[0, size)`
|
+| – | set | set | set | external `path`, `[offset, offset +
size)` |
+| – | – | set | – | this file, `[offset, EOF)`
(self-reference) |
+| – | – | – | set | this file, `[0, size)`
(self-reference) |
+| – | – | set | set | this file, `[offset, offset + size)`
(self-reference) |
+| – | – | – | – | nothing — invalid
|
+
+A self-reference typically points within the same Parquet file using `offset`
and
+`size`; the bytes are written between column chunks and are not otherwise
referenced by
+the footer. A self-reference is the absence of `path`, never an absolute path
back to
+the current file, so a file containing self-references is renamed or relocated
as a
+single unit.
+
+The referenced bytes are compressed with the same `CompressionCodec` as the one
+specified for the `inline` column.
Review Comment:
Should we point out `CompressionCodec` can differ per page?
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