hope to get some description of DC dependencies

I am studying the netweaver samples (especially the BPM) here.

In the each of the sample projects, programer needs to edit the dependencies tab.

For example, to add tc/bpem/mapping/facade and tc/je/sdo21/api to some project.

But the sample project never interprets why it needs the dependencies.

I guess those dependencies must provide some fundamental jars to the project, like the conception of jar library in common java/j2ee project.

I hope I can get a list depicting the functionality of the dependency and the class/interface of that dependency.

where can I found the docs?

And, is there any difference between the design time/Run time/Build Time. Why do I need to differ them during project implementation?