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<chapter id='dependency-resolution-package-modeling'>
<title>Package Modeling</title>
<sect1 id='dependency-resolution-package-modeling-constraint-satisfaction'>
<title>Constraint Satisfaction</title>
<sect2 id='dedependency-resolution-package-modeling-constraint-satisfaction-constraint-types'>
<title>Constraint Types</title>
<para>
Dependency resolution involves satisfaction of
many constraints:
<itemizedlist>
<listitem>
Persistent configuration parameters, like those that come from
make.profile, make.conf, and the /etc/portage directory.
</listitem>
<listitem>
Current command parameters, which may include options, atoms, or sets.
</listitem>
<listitem>
<link linkend='dependency-resolution-package-modeling-constraint-satisfaction-package-dependencies'>
Package Dependencies</link>
</listitem>
</itemizedlist>
</para>
</sect2>
<sect2 id='dependency-resolution-package-modeling-constraint-satisfaction-package-dependencies'>
<title>Package Dependencies</title>
<para>
Common types of package dependencies:
<itemizedlist>
<listitem>
Files required for building or installing. Downloads may
be necessary to satisfy these.
</listitem>
<listitem>
Other packages required to be installed for
buildtime or runtime.
</listitem>
<listitem>
Blockers that prevent conflicting packages from being installed
simultaneously.
</listitem>
</itemizedlist>
</para>
</sect2>
</sect1>
<sect1 id='dependency-resolution-package-modeling-conflicts'>
<title>Conflicts</title>
<sect2 id='dependency-resolution-package-modeling-blocker-conflicts'>
<title>Blocker Conflicts</title>
<para>
If one package blocks another package, the two packages
conflict such that they cannot be installed simultaneously.
These conflicts are often due to file collisions.
</para>
</sect2>
<sect2 id='dependency-resolution-package-modeling-slot-conflicts'>
<title>Slot Conflicts</title>
<para>
If two different packages that occupy the same slot are chosen
to satisfy dependencies, a slot conflict occurs. The two packages
cannot be installed simultaneously and therefore the respective
dependencies will not be satisfied simultaneously.
</para>
</sect2>
<sect2 id='dependency-resolution-package-modeling-indirect-conflicts'>
<title>Indirect Conflicts</title>
<para>
If the dependencies of two parent packages cannot be installed
simultaneously, it creates an indirect conflict between the parent
packages since their respective dependencies cannot be satisfied
simultaneously.
</para>
</sect2>
</sect1>
<sect1 id='dependency-resolution-package-modeling-dependency-neglection'>
<title>Dependency Neglection</title>
<para>
In order to significantly reduce the resources consumed by
the modeling process, the dependencies of
installed packages may be neglected.
</para>
<para>
If a more complete dependency calculation is desired,
there is a --complete-graph option which will ensure that the
dependencies of installed packages are properly considered.
</para>
</sect1>
</chapter>
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