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EMF Compare Match Engine: overwrite absoluteMetric() [message #509502]

Fri, 22 January 2010 16:09

Eclipse User

Originally posted by: d.hofmann.seeburger.de

Hi,

I evaluated EMF Compare and I think the generic match algorithm is
suitable for most cases. When I created a custom match engine, I found
that the very important method absoluteMetric() is private, so it's
impossible to overwrite it. The problem is specifically, that the basic
computation algorithm for the similarity metrics can't be changed and
also all weights are hardcoded.

Could you consider to make absoluteMetric() and also
relationsSimilarity() protected?

Thanks in advance!
David

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Re: EMF Compare Match Engine: overwrite absoluteMetric() [message #510360 is a reply to message #509502]

Wed, 27 January 2010 05:58

Laurent Goubet

Messages: 1902
Registered: July 2009

Senior Member

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David,

Implementing a custom matching engine for EMF Compare is usually a
matter of overriding findMostSimilar() and isSimilar(). Could you
elaborate on why these methods aren't satisfactory for your need?

Laurent Goubet
Obeo

David Hofmann wrote:
> Hi,
>
> I evaluated EMF Compare and I think the generic match algorithm is
> suitable for most cases. When I created a custom match engine, I found
> that the very important method absoluteMetric() is private, so it's
> impossible to overwrite it. The problem is specifically, that the basic
> computation algorithm for the similarity metrics can't be changed and
> also all weights are hardcoded.
>
> Could you consider to make absoluteMetric() and also
> relationsSimilarity() protected?
>
> Thanks in advance!
> David

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Re: EMF Compare Match Engine: overwrite absoluteMetric() [message #511671 is a reply to message #510360]

Tue, 02 February 2010 08:50

Eclipse User

Originally posted by: d.hofmann.seeburger.de

Hello Laurent,

I'm trying to explain for which reason I want to override these methods:

- For my model name similarity is not interesting, but it has a weight
of 80% by default

- for the position similarity, only URI equality is checked, not similarity

- the relation similarity compares the object's feature names. If you
have containment features, the children should also be involved in
comparison. Imagine you have some objects having children and
grandchilden, and only the grandchildren are different. The generic
match engine considers them as equal (similarity 1.0), which is not
correct from my point of view.
Consider the following example: the reference model contains the objects
ABC, and now B is removed. When comparing ABC and AC , C is matched with
B and no more siblings are compared (similarity is already 1.0). I would
like the match engine to compare the objects including their children,
so that it considers C and B as different.

When I tried to achieve this by overriding isSimilar() and
findMostSimilar(), I noticed that absoluteMetric() is also invoked from
mapLists() and recursiveMappings() (for creating match elements). So to
keep similarities consistent, I would have to re-implement the whole
call hierarchy of these methods, am I right?
Or can I implement my custom relation similarity only by overriding the
two methods you mentioned?

Thank you for your feedback,
David

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Re: EMF Compare Match Engine: overwrite absoluteMetric() [message #511859 is a reply to message #511671]

Wed, 03 February 2010 09:34

Laurent Goubet

Messages: 1902
Registered: July 2009

Senior Member

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David,

mapLists() and recursiveMappings() in turn call back isSimilar() and
findMostSimilar() to match your objects. Object C will not be matched
with B whatsoever if you override "IsSimilar()" and force it to return
false for these two objects. absoluteMetric() is more of an internal
process we use to handle generic case, and I don't believe it is
necessary to override it whatever the need (though I may have overlooked
a possibility).

Feel free to come back to us if you do not manage to achieve your goals
with only those two methods. Though we try to avoid it, we're not closed
to promoting internal to API when necessary.

Laurent Goubet
Obeo

David Hofmann wrote:
> Hello Laurent,
>
> I'm trying to explain for which reason I want to override these methods:
>
> - For my model name similarity is not interesting, but it has a weight
> of 80% by default
>
> - for the position similarity, only URI equality is checked, not similarity
>
> - the relation similarity compares the object's feature names. If you
> have containment features, the children should also be involved in
> comparison. Imagine you have some objects having children and
> grandchilden, and only the grandchildren are different. The generic
> match engine considers them as equal (similarity 1.0), which is not
> correct from my point of view.
> Consider the following example: the reference model contains the objects
> ABC, and now B is removed. When comparing ABC and AC , C is matched with
> B and no more siblings are compared (similarity is already 1.0). I would
> like the match engine to compare the objects including their children,
> so that it considers C and B as different.
>
> When I tried to achieve this by overriding isSimilar() and
> findMostSimilar(), I noticed that absoluteMetric() is also invoked from
> mapLists() and recursiveMappings() (for creating match elements). So to
> keep similarities consistent, I would have to re-implement the whole
> call hierarchy of these methods, am I right?
> Or can I implement my custom relation similarity only by overriding the
> two methods you mentioned?
>
> Thank you for your feedback,
> David

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Re: EMF Compare Match Engine: overwrite absoluteMetric() [message #512518 is a reply to message #511859]

Fri, 05 February 2010 06:06

Eclipse User

Originally posted by: d.hofmann.seeburger.de

Thank you Laurent,

it indeed works only by overriding the two methods, although the
absoluteMetric() is stored in the MatchModel, not the metric my custom
implementation computes. But that is not that interesting, since the
changes are shown correctly in the compare editor.

Thanks for your feedback,
David

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