OK, I'll start back a piece from your question.
When you do
<project>
...
<artifactId>a</artifactId>
...
<dependencies>
<dependency>
<groupId>foo</groupId>
<artifactId>bar</artifactId>
<version>1.0</version>
</dependency>
...
</dependencies>
...
</project>
what you are doing is telling maven that your project a needs foo:bar
and would, if its opinion counts, prefer to use version 1.0
If I have another project with
<project>
...
<artifactId>b</artifactId>
...
<dependencies>
<dependency>
<groupId>foo</groupId>
<artifactId>bar</artifactId>
<version>2.0</version>
</dependency>
...
</dependencies>
...
</project>
If project c lists a & b as it's dependencies, which version of
foo:bar will maven use?
a would prefer 1.0
b would prefer 2.0
There are rules which allow Maven to deterministically figure this out
(in this case the first dependency listed in project c will win,
unless c depends on foo:bar directly itself)
so for
<project>
...
<artifactId>c</artifactId>
...
<dependencies>
<dependency>
...
<artifactId>b</artifactId>
...
</dependency>
<dependency>
...
<artifactId>a</artifactId>
...
</dependency>
...
</dependencies>
...
</project>
c will end up using version 2.0.
The dependencyManagement is a way of more strongly hinting to maven
that it should use a specific version...
so since c does not directly depend on foo:bar, we don't really want
to add foo:bar as a dependency of project c.
By adding it as a dependencyManagement we can tell maven, oh by the
way, if you see this dependency, i'd really really like it if you can
use this version.
The other use case for dependencyManagement is to put it in a parent
pom... that way all the parent's children do not have to keep
specifying the version... in fact they can safely omit the version
-Stephen
2008/10/8 Wayne Fay <[EMAIL PROTECTED]>:
> Primarily, <dependencyManagement> does not actually attach an artifact
> dependency to a given project, while declaring a <dependency> does
> exactly that.
>
> So you could have a project with 10 items in depMgmt and no deps which
> tells users (and Maven) that it can be built all on its own.
>
> Wayne
>
> 2008/10/8 陈思淼 <[EMAIL PROTECTED]>:
>> <dependencyManagement>
>> <dependencies>
>> <dependency>
>> <groupId>test</groupId>
>> <artifactId>d</artifactId>
>> <version>1.0</version>
>> </dependency>
>> </dependencies>
>> </dependencyManagement>
>>
>>
>> <dependency>
>> <groupId>maven-test</groupId>
>> <artifactId>c</artifactId>
>> <scope>runtime</scope>
>> </dependency>
>> </dependencies>
>>
>
