All outputs are logically the same "type" of output. Within the SDKs, the "main" output is just the one that is output if no output tag is specified, and the one that matches the output type parameter of the DoFn. However, because there are multiple methods, including something that is a reasonable default, I think it's reasonable to distinguish between the two "methods" of outputting, while still just calling everything an "output". Having a main output does reduce the amount of code required for a DoFn that produces only a single output quite significantly, which is why it's still around.
Within the language-independent representations and most runners, there's no actual concept of main-vs-side outputs, except to support the default output(OutputT) method. On Wed, Apr 12, 2017 at 6:53 PM, Ankur Chauhan <an...@malloc64.com> wrote: > This question maybe obvious to others but why is there a distinction > between main output and additional outputs? Why not just have a simple list > of outputs where the first one is the Main one. > > -- AC > > Sent from my iPhone > > > On Apr 12, 2017, at 18:08, Melissa Pashniak <meliss...@google.com.INVALID> > wrote: > > > > I agree, I'll create a PR with the doc changes (the rename + text changes > > to make things more clear). I know of at least 2 places we refer to side > > outputs (programming guide and the "Design your pipeline" page). > > > > > > On Tue, Apr 11, 2017 at 5:34 PM, Thomas Groh <tg...@google.com.invalid> > > wrote: > > > >> I think that's a good idea. I would call the outputs of a ParDo the > "Main > >> Output" and "Additional Outputs" - it seems like an easy way to make it > >> clear that there's one output that is always expected, and there may be > >> more. > >> > >> On Tue, Apr 11, 2017 at 5:29 PM, Robert Bradshaw < > >> rober...@google.com.invalid> wrote: > >> > >>> We should do some renaming in Python too. Right now we have > >>> SideOutputValue which I'd propose naming TaggedOutput or something > >>> like that. > >>> > >>> Should the docs change too? > >>> https://beam.apache.org/documentation/programming- > >> guide/#transforms-sideio > >>> > >>> On Tue, Apr 11, 2017 at 5:25 PM, Kenneth Knowles > <k...@google.com.invalid > >>> > >>> wrote: > >>>> +1 ditto about sideInput and sideOutput not actually being related > >>>> > >>>> On Tue, Apr 11, 2017 at 3:52 PM, Robert Bradshaw < > >>>> rober...@google.com.invalid> wrote: > >>>> > >>>>> +1, I think this is a lot clearer. > >>>>> > >>>>> On Tue, Apr 11, 2017 at 2:24 PM, Stephen Sisk > <s...@google.com.invalid > >>> > >>>>> wrote: > >>>>>> strong +1 for changing the name away from sideOutput - the fact that > >>>>>> sideInput and sideOutput are not really related was definitely a > >>> source > >>>>> of > >>>>>> confusion for me when learning beam. > >>>>>> > >>>>>> S > >>>>>> > >>>>>> On Tue, Apr 11, 2017 at 1:56 PM Thomas Groh > >> <tg...@google.com.invalid > >>>> > >>>>>> wrote: > >>>>>> > >>>>>>> Hey everyone: > >>>>>>> > >>>>>>> I'd like to rename DoFn.Context#sideOutput to #output (in the Java > >>> SDK). > >>>>>>> > >>>>>>> Having two methods, both named output, one which takes the "main > >>> output > >>>>>>> type" and one that takes a tag to specify the type more clearly > >>>>>>> communicates the actual behavior - sideOutput isn't a "special" way > >>> to > >>>>>>> output, it's the same as output(T), just to a specified > >> PCollection. > >>>>> This > >>>>>>> will help pipeline authors understand the actual behavior of > >>> outputting > >>>>> to > >>>>>>> a tag, and detangle it from "sideInput", which is a special way to > >>>>> receive > >>>>>>> input. Giving them the same name means that it's not even strange > >> to > >>>>> call > >>>>>>> output and provide the main output type, which is what we want - > >>> it's a > >>>>>>> more specific way to output, but does not have different > >>> restrictions or > >>>>>>> capabilities. > >>>>>>> > >>>>>>> This is also a pretty small change within the SDK - it touches > >> about > >>> 20 > >>>>>>> files, and the changes are pretty automatic. > >>>>>>> > >>>>>>> Thanks, > >>>>>>> > >>>>>>> Thomas > >>>>>>> > >>>>> > >>> > >> >
