Module Archive Format


The structure of a module archive is very simple. It is a jar (zip) file containing other jars. The file has a .mar extension to distinguish it from plain jar files that contain classes or resources directly. For example:



Maven expects its artifacts to be self-contained: they should not reference any other artifact or file by name, only via Maven coordinates. MPS modules violate this restriction. A language module is represented by three jar files: the first contains the compiled classes, another jar contains the sources and the module descriptor, and a third jar file contains the generator model and classes. The structure of a solution module is the same apart from not containing a generator.

The self-containment is further violated by module jars referencing each other: the classes jar references the sources jar by name, and the generator jar is looked up by naming convention.

Since Maven stores all files in its repository under certain fixed names, it is not possible to store the MPS module jar files in the Maven repository directly. The solution that this plugin resorts to is to bundle individual module files in one module archive, or mar. As a side effect, it is possible to bundle several modules into one mar.