EnhancementEngine.canEnhance(ContentItem)

[Reto Bachmann-Gmür <re...@apache.org>]

Hello

I have some uncertainties understanding
EnhancementEngine.canEnhance(ContentItem).

When is this method called? Is it called immediately before
computeEnhancements or might other enhancement engines be called in
between? If the latter is the case then the ability to enhance an item
might depend on the items invoked in between. So is it ok to say first that
we can enhance and then throw an InvalidContentException on
computeEnhancement?

Cheers,
Reto

Re: EnhancementEngine.canEnhance(ContentItem)

[Rupert Westenthaler <ru...@gmail.com>]

Hi,

an EnhancementEngine MUST only be called if all other Engines that it
depends on have completed. This also includes the canEnhancement
method. Therefore it is guaranteed that all information required by
the Engine are already present on the call to canEnhance(..).

That said, most current EnhancementEngines do repeat checks of the
canEnhance(..) methods with the call to computeEnhancement(..). While
this would not be necessary based on the above definition it was still
very useful in debugging EnhancementJobManager implementations.

Regarding Exceptions: Engines are supposed to throw an EngineException
if they encounter an error during enhancing a ContentItem. This is
true for the canEnhance and the computeEnhancement method. So if an
Engine can detect some Error in the canEnhance method, that it can
throw this error early in the canEnhance(..) method. If it can not
enhance the ContentItem (e.g. because the configuration defines that
is should not process the current language) than an engine should just
return CANNOT_ENHANCE.

Hope this makes the intension more clear. Also have a look at the
documentation of EnhancementEngines [1] and the EnhancementJobManager
[2].

best
Rupert



[1] http://stanbol.apache.org/docs/trunk/components/enhancer/engines/
[2] http://stanbol.apache.org/docs/trunk/components/enhancer/enhancementjobmanager.html

On Sun, Mar 3, 2013 at 7:38 AM, Reto Bachmann-Gmür <re...@apache.org> wrote:
> Hello
>
> I have some uncertainties understanding
> EnhancementEngine.canEnhance(ContentItem).
>
> When is this method called? Is it called immediately before
> computeEnhancements or might other enhancement engines be called in
> between? If the latter is the case then the ability to enhance an item
> might depend on the items invoked in between. So is it ok to say first that
> we can enhance and then throw an InvalidContentException on
> computeEnhancement?
>
> Cheers,
> Reto



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