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From Marshall Schor <...@schor.com>
Subject Re: [jira] Closed: (UIMA-1352) java.lang.ClassCastException using find() with a SET index
Date Mon, 27 Jul 2009 12:21:19 GMT


Thilo Goetz wrote:
> See the Jira issue for the cause of the problem.  More
> comments below.
>
> Marshall Schor wrote:
>   
>> So, there may be 2 things to look at here - the actual error, described
>> above, and the more philosophical question on the behavior of moveTo -
>> this seems to require a sorting order if the item "moved to" is not
>> present in the index.  Perhaps this needs to be documented better.  And
>>     
>
> I'm not sure I understand your point about moveTo().  It requires the
> index to be sorted to make any sense (and the BagIndex moveTo() is broken,
> but that's a different issue
Will you be fixing this too?
> ).  moveTo(fs) will position the iterator such
> that any element "to the left" is smaller than fs, and all elements at the
> moved-to position and "to the right" of it are greater than or equal to
> fs.  It doesn't matter if the item "moved to" is in the index or not.
> Remember that equality here is defined with respect to the sort order of
> the index, it is not feature structure identity.  
Yes, this is something that is unexpected (to me), and I did forget this. 
> All this is documented,
> but maybe not as clearly as it could be.
>
>   
>> what if no sorting order was defined for the set index?
>>     
>
> Every set index has a sort order.  
This is the part that seems confusing, because our docs say that set
indexes do not enforce ordering, and the common definition for Sets does
not have an ordering concept.  Yet our docs say that the sort order for
sets is used to determine "equality" among candidates in the set:  from
section 2.4.1.7:

An index may define one or more /keys/. These keys determine the sort
order of the feature structures within a sorted index, and determine
equality for set indexes.

Perhaps this should also say something about the use of the sort order
in "moveTo(fs)" for sets?

> If that sort order is empty, it means
> that all FSs are equal for that index.  That in turn means that this
> index will contain at most 1 FS at any time.  It also means that moveTo()
> will always position the iterator at that one element, if it exists.
>
> Did that help at all?
>   
Yes, thanks for the clarifications.

-Marshall
> --Thilo
>
>
>
>   

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