Relation of PML + CAD + PDM wth SAP R/3

Hallo Friends,

I am not sure, if this is the right fourm to ask this question, or even this question makes any scense for you guy! so pls excuse me.

I would like to know what is the relation ship between CAD, PDM and SAP R/3 system.

What is CAD and PDM Systems, and what they have to do with SAP R/3 system.

Many thanks for your answers!

Haider Syed.