Allow defining artifacts and have DITA projects which depend on other projects

[raducoravu]

Description

Based on an older idea @georgebina, but today I also had a client with such needs.
In computer programming we split a larger project in subprojects. Those subprojects may have code which refers to other subprojects. We use for example Maven to pack each subproject as an artifact which can be used in a larger project.

Assume we have a team working on documenting a specific part of a product. They could have their own DITA XML project hosted on Git/SVN. So maybe you have multiple teams, each working on a specific DITA XML project which documents a part of the product. And each team has their own GitHub repo.
Then you have another DITA XML project which incorporates in its DITA Map references to the submaps developed in those smaller projects.
How does that work today? I need to check out all those subprojects locally and the "main.ditamap" needs to have references like "mapref href="../../chapter.ditamap"".
Maybe I do not want to checkout all those subprojects locally as I am not making changes to them, I'm just using their content to build a larger publication

Possible Solution

Maybe the DITA OT project file for a certain project could specify on what other project artifacts it depends. Those artifacts would already be published somewhere. So when the DITA OT project file is run, those artifacts it depends on would be unpacked and used. Probably this would mean the entire sources would need to be moved to a temporary files folder and the published output built from that.

Potential Alternatives

This particular client uses as a workaround in the DITA Map of the main project a mapref to the HTTP location of the submap in the Subversion repository. So they have a mapref like this:

  <topicref
  href="https://.../samples/dita/garage/garage.ditamap"
  format="ditamap" scope="external"/> 

and they rely on the HTTP connection to retrieve the content of the submap.