Looking at Google these two items are not connected. Composite libraries are something to do with Windows development, and, therefore, are not to do with mainframes, while distributed libraries are something to do with books. I only looked at the first Google reslts for each term so there may be other more related stuff. But Google is probably your friend here (and in many other cases).
The problem I have is that people can explain things quickly but I can only comprehend slowly.