Data integration is the problem of combining data residing in different sources and providing users with a unified view of them.

Lenzerini, Maurizio. (2002). Data Integration: A Theoretical Perspective. Proceedings of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems. 233-246. [Paper]

A set of techniques that enable building systems geared for flexible sharing and integration of data across multiple autonomous data providers

Doan, AnHai, Alon Halevy, and Zachary Ives. Principles of data integration. Elsevier, 2012. [ACM DL]