GSoC 15 - Dependency Calculation using SAT

[Mihai Moldovan]

On 21.03.2015 02:00 PM, Jackson Isaac wrote:
>>> Do you mean like in Portfile we have:
>>
>> Did you mean PortIndex instead of Portfile?
>>
> 
> Yes, I meant PortIndex. Sorry for the typo.

Ok, that makes more sense. Thanks.


> So we will have to calculate the dependency tree while we install.
> Since there can be many variants possible and each will have different
> dependencies.

Yes, quite so. That's what is currently being done.


> Using SAT method we will be defining minimal dependencies and these
> dependencies will be further checked for their dependencies or we need
> to still define all the dependencies for each package?

Keep in mind that variants can also *remove* dependencies (at the
moment.) In that case, the base line dependencies you just called
minimal could *shrink* by activating a variant.


> Eg. x depends on y. so in portfile of x say it depends on y. Now we
> will check if y depends on any a,b,c further. Like this compute
> different possible combinations and select the best course and also
> taking the variant into account (using Boolean).

As a side note: a (as far as I've seen) very good/understandable example
of how SAT is being used as a package dependency resolution is given in
this slide show:
https://files.opensuse.org/opensuse/en/b/b9/Fosdem2008-solver.pdf

Taken from here:
https://en.opensuse.org/openSUSE:Libzypp_satsolver

One benefit of using a SAT solver for dependency calculation is to
support cyclic dependencies. With the current implementation, this is
impossible.



Mihai

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