[lyo-dev] Use of Maven dependencyManagement elements

["Jim Amsden" <jamsden@xxxxxxxxxx>]

While updating eclipse/Lyo eclipse project
dependencies, I came across a use of the Maven <dependencyManagement>
element that I don't quite understand. 

Some of the OSLC4J projects, such as
org.eclipse.lyo.client/org.eclipse.lyo.client.java, contain <dependencyManagement>
elements in their pom.xml files. These don't hurt anything, but don't make
sense for projects that don't have child module projects because there
are no modules that will inherit the versions. 

My understanding of Maven dependency
management is that aggregrator projects can be used to to organize child
projects or modules, and can define properties and dependencies that specify
the preferred versions that child modules should use. This allows common
property and dependency versions to be listed in one place. Child modules
still have to declare all the dependencies they use (versions are inherited,
not the managed dependencies), but they don't have to redundantly specify
the versions. 

OSLC4J does have an aggregator project,
org.eclipse.lyo.oslc4j.build whose pom.xml file declares the modules that
makeup OSLC4J.
        <modules>
         
      <module>../org.eclipse.lyo.oslc4j.core</module>
         
      <module>../org.eclipse.lyo.oslc4j.provider.jena</module>
         
      <module>../org.eclipse.lyo.oslc4j.provider.json4j</module>
         
      <module>../org.eclipse.lyo.oslc4j.wink</module>
         
      <module>../org.eclipse.lyo.oslc4j.registry</module>
         
      <module>../org.eclipse.lyo.core.query</module>
         
      <module>../org.eclipse.lyo.core.trs</module>
         
      <module>../org.eclipse.lyo.core.utils</module>
        </modules>

However, this aggregator project does
not define any common OSLC4J dependencyManagement dependencies, nor do
any of the module project declare org.eclipse.lyo.oslc4j.build to be their
parent project. As a result, all of the OSLC4J projects redundantly and
in some cases inconsistently declare their own dependency versions.

Question: Why doesn't this aggregrator
project include org.eclipse.lyo.client/org.eclipse.lyo.client.java? Is
that just missing? It is delivered as part of the OSLC4J SDK.

I addition, module projects such as
org.eclipse.lyo.client/org.eclipse.lyo.client.java, contain dependencyManagement
elements, while these are leaf modules, they are not the parent module
of any other module, so there are no modules to inherit the dependencyManagement
dependency versions.

Does anyone have any insight on why
OSLC4J uses of Maven dependencyManagement elements this way?

Possible actions as part of the 2.2.0
dependency update release:

1. Remove all dependencyManagement elements
from the OSLC4J projects, and merge the dependencies into the existing
<dependencies> element.

2. Use mvn dependency:analyze to clean
up the unused or missing dependency references in the pom.xml files

3. Define all the common OSLC4J dependencies
and versions in a dependencyManagement element in  org.eclipse.lyo.oslc4j.build

4. Add <parent> elements in each
of the OSLC4J module projects to refer to org.eclipse.lyo.oslc4j.build

5. Remove all dependency versions from
the OSLC4J module projects, and inherit the versions from the org.eclipse.lyo.oslc4j.build
parent

6. Also add a lyo.verson property to
org.eclipse.lyo.oslc4j.build and use this property value to specify the
version of each module. This way the version of OSLC4J can be specified
in one place.



Jim Amsden, Senior Technical Staff Member
OSLC and Linked Lifecycle Data
919-525-6575