One thing I can answer is, the relationship between SAP and IT companies like Infosys.
So first of all, SAP is a product based organization, which develops softwares in ERP sector (mainly) , which is required to run your entire business..so companies like for example Airbus...who wishes to run their business on SAP , will purchase the software. And after that they will require a huge team to handle that software..so for that they outsoure it to service based companies like Infosys/TCS/Atos, etc..
So SAP is software making company and Infosys is helping to run and handle that software and client (Airbus) business..
Hope this helps..thanks