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From Grant Ingersoll <gsing...@apache.org>
Subject Re: TokenStream and Token APIs
Date Mon, 20 Oct 2008 13:47:28 GMT

On Oct 19, 2008, at 7:08 PM, Michael Busch wrote:

> Grant Ingersoll wrote:
>>
>> On Oct 19, 2008, at 12:56 AM, Mark Miller wrote:
>>
>>> Grant Ingersoll wrote:
>>>>
>>>> Bear with me, b/c I'm not sure I'm following, but looking at https://issues.apache.org/jira/browse/LUCENE-1422

>>>> , I see at least 5 different implemented Attributes.
>>>>
>>>> So, let's say I add a 5 more attributes and now have a total of  
>>>> 10 attributes. Are you saying that I then would have,  
>>>> potentially, 10 different variables that all point to the token  
>>>> as in the code snippet above where the casting takes place? Or  
>>>> would I just create a single "Super" attribute that folds in all  
>>>> of my new attributes, plus any other existing ones? Or, maybe,  
>>>> what I would do is create the 5 new attributes and then 1 new  
>>>> attribute that extends all 10, thus allowing me to use them  
>>>> individually, but saving me from having to do a whole ton of  
>>>> casting in my Consumer.
>>> Potentially one consumer doing 10 things, but not likely right? I  
>>> mean, things will stay logical as they are now, and rather than a  
>>> super consumer doing everything, we will still have a chain of  
>>> consumers each doing its own piece. So more likely, maybe  
>>> something comes along every so often (another 5, over *much* time,  
>>> say) and each time we add a Consumer that uses one or two  
>>> TokenStream types. And then its just an implementation detail on  
>>> whether you make a composite TokenStream - if you have added 10  
>>> new attributes and see it fit to make one consumer use them all,  
>>> sure, make a composite, super type, but in my mind, the way its  
>>> done in the example code is clearer/cleaner for a handful of  
>>> TokenStream types. And even if you do make the composite,super  
>>> type, its likely to just be a sugar wrapper anyway - the  
>>> implementation for say, payload and positions, should probably be  
>>> maintained in their own classes anyway.
>>
>> Well, there are 5 different attributes already, all of which are  
>> commonly used.  Seems weird to have to cast the same var 5  
>> different ways.  Definitely agree that one would likely deal with  
>> this by wrapping, but then you end up either needing to extend your  
>> wrapper or add new wrappers...
>
> Well yes, there are 5 attributes, but n neither of the core  
> tokenstreams and -filters that I changed in my patch did I have to  
> use more than two or three of those. Currently the only attributes  
> that are really used are PositionIncrementAttribute and  
> PayloadAttribute. And the OffsetAttribute when TermVectors are  
> turned on.
>
> Even in the indexing chain currently we don't have a single consumer  
> that needs all attributes. The FreqProxWriter needs positions and  
> payloads, the TermVectorsWriter needs positions and offsets.


I have an application that uses all the attributes of a Token, or at  
least, almost all of them.  There are many uses for Lucene's analysis  
code that have nothing to do with indexing, Consumers or even Lucene.

>
>
> Also, you don't have to cast the same variable multiple times. In  
> the current patch you would call e. g.  
> token.getAttribute(PayloadAttribute.class) and keep a reference to  
> it in the consumer or filter.
>
> IMO even calling getAttribute() 5 times or so and storing the  
> references wouldn't be so bad. And if you really don't like it you  
> could make a wrapper as you said. You also mentioned the  
> disadvantages of the wrapper, e. g. that you would have to extend it  
> to add new attributes. But then, isn't that the same disadvantage  
> the current Token API has?

True.  I didn't say the idea was bad, in fact I mostly like it, I was  
just saying I'd like to explore how it would work in practice and the  
main thing that struck me was all the casting or all the references.   
Since it's likely that you only deal with a Token one at a time,  
you're right, it's probably not a big deal other than the code looks  
funny, IMO.

>
>
> You could even use the new API in exact the same way as the old one.  
> Just create a subclass of Token that has all members you need and  
> don't add any attributes.
>
> So I think the new API adds more flexibility, and still offers to  
> use it in the same way as the old one. I however think the  
> recommended best practice should be to use the new attributes, for  
> reusability of consumers that only need certain attributes.

Perhaps it would be useful for Lucene to offer exactly one subclass of  
Token that we guarantee will always have all known Attributes (i.e.  
the ones Lucene provides)  available to it for casting purposes.

>
>
> However, please let me know if you have any concrete recommendations  
> about changing the API in LUCENE-1422.

I thought those concerns were pretty concrete...  :-)

> There might be better ones than the APIs I came up with.

I think the APIs in the 2nd patch look pretty reasonable.


-Grant

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