One or more [IRI](https://en.wikipedia.org/wiki/Internationalized_Resource_Identifier)s
identifying resources for installing or enabling the software named in
the `package` field. Implementations may provide resolvers which map
these software identifier IRIs to some configuration action; or they can
use only the name from the `package` field on a best effort basis.

For example, the IRI <https://packages.debian.org/bowtie> could
be resolved with `apt-get install bowtie`. The IRI
<https://anaconda.org/bioconda/bowtie> could be resolved with `conda install -c bioconda bowtie`.

IRIs can also be system independent and used to map to a specific
software installation or selection mechanism.
Using [RRID](https://www.identifiers.org/rrid/) as an example:
<https://identifiers.org/rrid/RRID:SCR_005476>
could be fulfilled using the above-mentioned Debian or bioconda
package, a local installation managed by [Environment Modules](https://modules.sourceforge.net/),
or any other mechanism the platform chooses. IRIs can also be from
identifier sources that are discipline specific yet still system
independent. As an example, the equivalent [ELIXIR Tools and Data
Service Registry](https://bio.tools) IRI to the previous RRID example is
<https://bio.tools/tool/bowtie2/version/2.2.8.>
If supported by a given registry, implementations are encouraged to
query these system independent software identifier IRIs directly for
links to packaging systems.

A site specific IRI can be listed as well. For example, an academic
computing cluster using Environment Modules could list the IRI
`<https://hpc.example.edu/modules/bowtie-tbb/1.22`> to indicate that
`module load bowtie-tbb/1.1.2` should be executed to make available
`bowtie` version 1.1.2 compiled with the TBB library prior to running
the accompanying `Workflow` or `CommandLineTool`. Note that the example IRI
is specific to a particular institution and computing environment as
the Environment Modules system does not have a common namespace or
standardized naming convention.

This last example is the least portable and should only be used if
mechanisms based off of the `package` field or more generic IRIs are
unavailable or unsuitable. While harmless to other sites, site specific
software IRIs should be left out of shared CWL descriptions to avoid
clutter.
