How does SAP NetWeaver differentiate with sap XI?

SAP netweaver is having ABAP and Java stack for diffecrent functional modules.

where as XI/PI is userd for processing messages/files/XML files from one systems to othere with in  sap or non sap systems.

SAP netweaver is one platform under which SAP XI(exchange Infrastructure), SAP PI(Process Integration ) and now SAP PO (Process Orchestration) are a part. 

Hello,Sap XI (later on PI and even recently PO) are one part of the global SAP Netweaver platform.SAP Netweaver platform is also composed of other components like: 

- SAP Enterprise Portal (EP)

- SAP Business Inteligence (BI)

- SAP Web Application Server (WAS)

- SAP Master Data Management (MDM)

...and many others