I opened https://github.com/google/flatbuffers/issues/5688 to try to get some clarity.
On Tue, Dec 24, 2019 at 12:13 PM Wes McKinney <wesmck...@gmail.com> wrote: > On Tue, Dec 24, 2019 at 2:47 AM Micah Kornfield <emkornfi...@gmail.com> > wrote: > >> > >> If we were to make the same kinds of forward/backward compatibility > >> guarantees as with Flatbuffers it could create a lot of work for > >> maintainers. > > > > Does it pay to follow-up with the flatbuffer project to understand if > the forward/backward compatibility guarantees the flatbuffers provide > extend to their JSON format? > > I spent a few minutes looking at the Flatbuffers codebase and > documentation and did not find anything, so this seems like useful > information to have regardless. > > > > > On Sun, Dec 15, 2019 at 11:17 AM Wes McKinney <wesmck...@gmail.com> > wrote: > >> > >> I'd be open to looking at a proposal for a human-readable text > >> representation, but I'm definitely wary about making any kind of > >> cross-version compatibility guarantees (beyond "we will do our best"). > >> If we were to make the same kinds of forward/backward compatibility > >> guarantees as with Flatbuffers it could create a lot of work for > >> maintainers. > >> > >> On Thu, Dec 12, 2019 at 12:43 AM Micah Kornfield <emkornfi...@gmail.com> > wrote: > >> > > >> > > > >> > > With these two together, it would seem not too difficult to create > a text > >> > > representation for Arrow schemas that (at some point) has some > >> > > compatibility guarantees, but maybe I'm missing something? > >> > > >> > > >> > I think the main risk is if somehow flatbuffers JSON parsing doesn't > handle > >> > backward compatible changes to the arrow schema message. Given the > way the > >> > documentation is describing the JSON functionality I think this would > be > >> > considered a bug. > >> > > >> > The one downside to calling the "schema" canonical is the flatbuffers > JSON > >> > functionality only appears to be available in C++ and Java via JNI, > so it > >> > wouldn't have cross language support. I think this issue is more one > of > >> > semantics though (i.e. does the JSON description become part of the > "Arrow > >> > spec" or does it live as a C++/Python only feature). > >> > > >> > -Micah > >> > > >> > > >> > On Tue, Dec 10, 2019 at 10:51 AM Christian Hudon < > chr...@elementai.com> > >> > wrote: > >> > > >> > > Micah: I didn't know that Flatbuffers supported serialization > to/from JSON, > >> > > thanks. That seems like a very good start, at least. I'll aim to > create a > >> > > draft pull request that at least wires everything up in Arrow so we > can > >> > > load/save a Schema.fbs instance from/to JSON. At least it'll make > it easier > >> > > for me to see how Arrow schemas would look in JSON with that. > >> > > > >> > > Otherwise, I'm still gathering requirements internally here. For > example, > >> > > one thing that would be nice would be to be able to output a JSON > Schema > >> > > from at least a subset of the Arrow schema. (That way our users > could start > >> > > by passing around JSON with a given schema, and transition pieces > of a > >> > > workflow to Arrow as they're ready.) But that part can also be done > outside > >> > > of the Arrow code, if deemed not relevant to have in the Arrow > codebase > >> > > itself. > >> > > > >> > > One core requirement for us, however, would be eventual > compatibility > >> > > between Arrow versions for a given text representation of a schema. > >> > > Meaning, if you have a text description of a given Arrow schema, > you can > >> > > load it into different versions of Arrow and it creates a valid > Schema > >> > > Flatbuffer description, that Arrow can use. Wes, were you thinking > of that, > >> > > or of something else, when you wrote "only makes sense if it is > offered > >> > > without any backward/forward compatibility guarantees"? > >> > > > >> > > For the now, or me, assuming the JSON serialization done by the > Flatbuffer > >> > > libraries is usable, it seems we have all the pieces to make this > happen: > >> > > 1) The binary Schema.fbs data structures has to be compatible > between > >> > > different versions of Arrow, otherwise two processes with different > Arrow > >> > > versions won't be able to interoperate, no? > >> > > 2) The Flatbuffer <-> JSON serialization supplied by the Flatbuffers > >> > > library also has to be compatible between different versions of the > >> > > Flatbuffers library, since the main use case seems to be storing > >> > > Flatbuffers assets into version control. Breaking changes there > will also > >> > > be painful to their users. > >> > > > >> > > With these two together, it would seem not too difficult to create > a text > >> > > representation for Arrow schemas that (at some point) has some > >> > > compatibility guarantees, but maybe I'm missing something? > >> > > > >> > > Thanks, > >> > > > >> > > Christian > >> > > > >> > > Le lun. 9 déc. 2019, à 07 h 00, Wes McKinney <wesmck...@gmail.com> > a > >> > > écrit : > >> > > > >> > > > The only "canonical" representation of schemas at the moment is > the > >> > > > Flatbuffers data structure [1] > >> > > > > >> > > > Having a human-readable/parseable text representation I think only > >> > > > makes sense if it is offered without any backward/forward > >> > > > compatibility guarantees. > >> > > > > >> > > > Note I had previously opened > >> > > > https://issues.apache.org/jira/browse/ARROW-3730 where I noted > that > >> > > > there's no way (aside from generating the Flatbuffers messages) to > >> > > > generate a schema representation that can be used later to > reconstruct > >> > > > a schema in a program. If such a representation were human > >> > > > readable/editable that seems beneficial. > >> > > > > >> > > > > >> > > > > >> > > > [1]: > https://github.com/apache/arrow/blob/master/format/Schema.fbs > >> > > > > >> > > > On Sat, Dec 7, 2019 at 11:56 AM Maarten Ballintijn < > maart...@xs4all.nl> > >> > > > wrote: > >> > > > > > >> > > > > > >> > > > > Is there a syntax specified for schemas? > >> > > > > > >> > > > > Cheers, > >> > > > > Maarten. > >> > > > > > >> > > > > > >> > > > > > On Dec 6, 2019, at 5:01 PM, Micah Kornfield < > emkornfi...@gmail.com> > >> > > > wrote: > >> > > > > > > >> > > > > > Hi Christian, > >> > > > > > As far as I know no-one is working on a canonical text > representation > >> > > > for > >> > > > > > schemas. A JSON serializer exists for integration test > purposes, but > >> > > > > > IMO it shouldn't be relied upon as canonical. > >> > > > > > > >> > > > > > It looks like Flatbuffers supports serialization to/from JSON > [1 > >> > > > > > < > https://google.github.io/flatbuffers/flatbuffers_guide_use_cpp.html > >> > > > >], > >> > > > > > using that functionality might be a promising avenue to > pursue for a > >> > > > human > >> > > > > > readable schema. I could see adding a helper method someplace > under > >> > > > IPC for > >> > > > > > this. Would that meet your needs? I think if there are other > >> > > > > > requirements, then a proposal would be welcome. Ideally, a > solution > >> > > > would > >> > > > > > not require additional build/runtime dependencies. > >> > > > > > > >> > > > > > > >> > > > > > Thanks, > >> > > > > > Micah > >> > > > > > > >> > > > > > [1] See Text & schema parsing > >> > > > > > > https://google.github.io/flatbuffers/flatbuffers_guide_use_cpp.html > >> > > > > > > >> > > > > > On Fri, Dec 6, 2019 at 1:26 PM Christian Hudon < > chr...@elementai.com > >> > > > > >> > > > wrote: > >> > > > > > > >> > > > > >> Hi, > >> > > > > >> > >> > > > > >> For the uses I would like to make of Arrow, I would need a > >> > > > human-readable > >> > > > > >> and -writable version of an Arrow Schema, that could be > converted to > >> > > > and > >> > > > > >> from the Arrow Schema C++ object. Going through the doc for > 0.15.1, > >> > > I > >> > > > don't > >> > > > > >> see anything to that effect, with the closest being the > ToString() > >> > > > method > >> > > > > >> on DataType instances, but which is meant for debugging > only. (I > >> > > need > >> > > > an > >> > > > > >> expression of an Arrow Schema that people can read, and that > can > >> > > live > >> > > > > >> outside of the code for a particular operation.) > >> > > > > >> > >> > > > > >> Is a text representation of an Arrow Schema something that > is being > >> > > > worked > >> > > > > >> on now? If not, would you folks be interested in me putting > up an > >> > > > initial > >> > > > > >> proposal for discussion? Any design constraints I should pay > >> > > > attention to, > >> > > > > >> then? > >> > > > > >> > >> > > > > >> Thanks, > >> > > > > >> > >> > > > > >> Christian > >> > > > > >> -- > >> > > > > >> > >> > > > > >> > >> > > > > >> │ Christian Hudon > >> > > > > >> > >> > > > > >> │ Applied Research Scientist > >> > > > > >> > >> > > > > >> Element AI, 6650 Saint-Urbain #500 > >> > > > > >> > >> > > > > >> Montréal, QC, H2S 3G9, Canada > >> > > > > >> Elementai.com > >> > > > > >> > >> > > > > > >> > > > > >> > > > >> > > > >> > > -- > >> > > > >> > > > >> > > │ Christian Hudon > >> > > > >> > > │ Applied Research Scientist > >> > > > >> > > Element AI, 6650 Saint-Urbain #500 > >> > > > >> > > Montréal, QC, H2S 3G9, Canada > >> > > Elementai.com > >> > > >
