On Sat, 22 Jan 2022 at 20:27, Rok Mihevc <rok.mih...@gmail.com> wrote: > > Thanks for the input Weston! > > How about arrow/experimental/format/ExtensionTypes.fbs or > arrow/format/ExtensionTypes.fbs for language independent schema and > loosely arrow/<IMPLEMENTATION>/extensions for implementations? > > Having machine readable definitions could perhaps be useful for > generating implementations in some cases.
Is it useful to put this in a flatbuffer file? Based on the list from Weston just below, I think this will mostly contain a *description* of those different aspect (a specification of the extension type), and there is no data that actually fits in a flatbuffer table? In that case a plain text (eg markdown) file seems more fitting? > > > * The name of the extension type (to go in ARROW:extension:name) > > * A description of the extension type and how it should be used > > * The storage type of the extension type > > * The format and meaning of the content that will go into > > ARROW:extension:metadata > > These sound pretty complete! > > I'll wait for a couple of days to see if there's more input and then > draft a PR. Do we need a vote on this? > > > Best, > Rok > > On Fri, Jan 21, 2022 at 3:07 AM Weston Pace <weston.p...@gmail.com> wrote: > > > > Those all seem to be C++ locations. If we want to define > > cross-implementation "Well Known Extension Types" then it seems we > > would want to come up with some kind of language independent agreement > > (could just be a markdown file but maybe there is some advantage to > > having something programmatically consumable) describing: > > > > * The name of the extension type (to go in ARROW:extension:name) > > * A description of the extension type and how it should be used > > * The storage type of the extension type > > * The format and meaning of the content that will go into > > ARROW:extension:metadata > > > > I think (but am not sure) that, since these are metadata keys, we are > > supposed to stick to printable ASCII for values (for backwards > > compatibility). > > > > For example, in the docs, we currently have this little blurb about a > > theoretical tensor extension type: > > > > > tensor (multidimensional array) stored as Binary values and > > > having serialized metadata indicating the data type and shape > > > of each value. This could be JSON like {'type': 'int8', 'shape': > > > [4, 5]} for a 4x5 cell tensor. > > > > In my mind this file would be somewhat analogous to the way that > > schema.fbs is the cross implementation "ground truth" for our logical > > types. > > > > Then the C++ implementation would be free to put the implementation > > (I'd vote for arrow/cpp/extensions but a separate repo is probably ok. > > I'm -1 on arrow/extensions/...) > > > > On Thu, Jan 20, 2022 at 3:20 PM Rok Mihevc <rok.mih...@gmail.com> wrote: > > > > > > To continue the ExtensionType part of this thread - I would like to > > > add TensorArray [1] as an ExtensionType to Arrow but we have not yet > > > agreed on an "official" location for "Well Known Extension Types". > > > > > > Where could we put these? Some suggestions: > > > > > > * implementation folders (e.g. arrow/cpp/extensions/tensor_array.h) > > > * extensions folder (e.g. arrow/extensions/cpp/tensor_array.h) > > > * separate repo (e.g. > > > github.com/apache/arrow_extensions/cpp/tensor_array.h) > > > > > > I'd be happy to also gather other Well Known Extension Types into one > > > location if this moves forward. > > > > > > Rok > > > > > > [1] https://github.com/apache/arrow/pull/8510#issuecomment-991150389 > > > > > > On Sat, May 1, 2021 at 12:12 PM Andrew Lamb <al...@influxdata.com> wrote: > > > > > > > > I agree with others on this thread. Thanks for writing this down Micah > > > > > > > > On Fri, Apr 30, 2021 at 11:16 AM Antoine Pitrou <anto...@python.org> > > > > wrote: > > > > > > > > > > > > > > I concur with both what Wes and Micah said. > > > > > > > > > > As for temporal types, they have wide-spread use and their semantics > > > > > require dedicated treatment for arithmetic and conversion, so it's > > > > > helpful to define dedicated types for them, as opposed to mere > > > > > annotations. > > > > > > > > > > Regards > > > > > > > > > > Antoine. > > > > > > > > > > > > > > > Le 30/04/2021 à 16:40, Wes McKinney a écrit : > > > > > > I agree that the bar for adding new types to the Type union in > > > > > > Schema.fbs > > > > > > should be quite high going forward. Using extension types > > > > > > increasingly > > > > > for > > > > > > adding specializations of built-in types will mean less burden for > > > > > > implementations to simply "propagate forward" this data (by > > > > > > preserving > > > > > the > > > > > > extra metadata) even if they don't understand what it does. It > > > > > > would be > > > > > > nice, therefore, to put us on a path to expanding our set of > > > > > > "official" > > > > > > extension types (which would include things like JSON or UUID) > > > > > > since some > > > > > > libraries may choose to implement convenience containers for these > > > > > > for > > > > > > usability. > > > > > > > > > > > > On Fri, Apr 30, 2021 at 9:22 AM Brian Hulette <bhule...@apache.org> > > > > > wrote: > > > > > > > > > > > >> +1 this looks good to me. > > > > > >> > > > > > >> My only concern is with criteria #3 " Is the underlying encoding > > > > > >> of the > > > > > >> type already semantically supported by a type?". I think this is a > > > > > >> good > > > > > >> criteria, but it's inconsistent with the current spec. By that > > > > > >> criteria > > > > > >> some existing types (Timestamp, Time, Duration, Date) should be > > > > > >> well > > > > > known > > > > > >> extension types, right? > > > > > >> > > > > > >> Perhaps we should explicitly indicate these types are > > > > > >> grandfathered in > > > > > [1] > > > > > >> because they existed before extension types, to avoid tension with > > > > > >> this > > > > > >> criteria. > > > > > >> > > > > > >> Brian > > > > > >> > > > > > >> [1] https://en.wikipedia.org/wiki/Grandfather_clause > > > > > >> > > > > > >> On Thu, Apr 29, 2021 at 9:13 PM Jorge Cardoso Leitão < > > > > > >> jorgecarlei...@gmail.com> wrote: > > > > > >> > > > > > >>> Thanks for writing this. > > > > > >>> > > > > > >>> I agree. That is a good decision tree. +1 > > > > > >>> > > > > > >>> Best, > > > > > >>> Jorge > > > > > >>> > > > > > >>> > > > > > >>> On Thu, Apr 29, 2021 at 6:08 PM Micah Kornfield > > > > > >>> <emkornfi...@gmail.com > > > > > > > > > > > >>> wrote: > > > > > >>> > > > > > >>>> The discussion around adding another interval type to the > > > > > >>>> Schema.fbs > > > > > >>> raises > > > > > >>>> the issue of when do we decide to add a new type to the > > > > > >>>> Schema.fbs vs > > > > > >>> using > > > > > >>>> other means (primarily extension types [1]). > > > > > >>>> > > > > > >>>> A few criteria come to mind that could help decide (feedback > > > > > >>>> welcome): > > > > > >>>> > > > > > >>>> 1. Is the type a new parameterization of an existing type? > > > > > >>>> - If Yes, and we believe the parameterization is useful and > > > > > >>>> can > > > > > be > > > > > >>> done > > > > > >>>> in a forward/backward compatible manner then we would update > > > > > >> Schema.fbs. > > > > > >>>> > > > > > >>>> 2. Does the type itself have its own specification for > > > > > >>>> processing > > > > > >> (e.g. > > > > > >>>> JSON, BSON, Thrift, Avro, Protobuf)? > > > > > >>>> - If yes, we would NOT add them to Schema.fbs. I think this > > > > > >>>> would > > > > > >>>> potentially yield too many new types. > > > > > >>>> > > > > > >>>> 3. Is the underlying encoding of the type already semantically > > > > > >> supported > > > > > >>>> by a type? (e.g. if we want to encode physical lengths like > > > > > >>>> meters > > > > > >> these > > > > > >>>> can be represented by an integer). > > > > > >>>> - If yes, we would NOT update the specification. This seems > > > > > >>>> like > > > > > >> the > > > > > >>>> exact use-case that extension types are meant for. > > > > > >>>> > > > > > >>>> * How does this apply to Interval? * > > > > > >>>> Interval extends an existing type in the specification and > > > > > >>>> multiple > > > > > >>> "packed > > > > > >>>> fields" cannot be easily communicated with the current version > > > > > >>>> of the > > > > > >>>> specification. Hence, I feel comfortable making the addition to > > > > > >>> Schema.fbs > > > > > >>>> > > > > > >>>> * What does this mean for other common types? * > > > > > >>>> > > > > > >>>> I think as types come up that are very common but we don't want > > > > > >>>> to add > > > > > >> to > > > > > >>>> the Schema.fbs we should invest in formalizing them as "Well > > > > > >>>> Known" > > > > > >>>> Extension types. In this scenario, we would update the > > > > > >>>> specification > > > > > >> to > > > > > >>>> include how to specify the extension type metadata (and still > > > > > >>>> require > > > > > >> at > > > > > >>>> least two libraries support the Extension type before inclusion > > > > > >>>> as > > > > > >> "Well > > > > > >>>> Known"). > > > > > >>>> > > > > > >>>> * Practical implications * > > > > > >>>> > > > > > >>>> I think this means the type system in Schema.fbs is mostly closed > > > > > (i.e. > > > > > >>>> there is a high bar for adding new types). One potentially > > > > > >>>> useful type > > > > > >> to > > > > > >>>> have would be a "packed struct" that supports something similar > > > > > >>>> to > > > > > >> python > > > > > >>>> struct library [2]. I think this would likely cover many > > > > > >>>> extension > > > > > >> type > > > > > >>>> use-cases. > > > > > >>>> > > > > > >>>> Thoughts? > > > > > >>>> > > > > > >>>> -Micah > > > > > >>>> > > > > > >>>> [1] > > > > > https://arrow.apache.org/docs/format/Columnar.html#extension-types > > > > > >>>> [2] https://docs.python.org/3/library/struct.html > > > > > >>>> > > > > > >>> > > > > > >> > > > > > > > > > > >