Data integration is the process of combining multiple data sources under a unified view/layer/schema/vocabulary. I.e. something that one can formulate queries to/over which can combine data from different sources. So if a set of data sources is integrated, one can formulate queries that seemlessly use multiple sources as if they were a single source.

Relevant Articles and Tutorials

• Wikipedia’s page on Data Integration
• Wikipedia’s page on Semantic Integration
• Data Integration: A Theoretical Perspective
  • Paper with a theoretical account of data integration with complexity results
• Logic-Based Techniques in Data Intergration
  • “his paper describes several languages for describing contents of data sources, the tradeoffs between them, and the associated reformulation algorithms.”
• Ontology-Based Data Access with Databases: A Short Course
• GeeksForGeeks’ Article on LAV
• GeeksForGeeks’ Article on GAV
• Ontop
  • OBDA system
• PostgreSQL’s Foreign Data Wrappers
  • Can access other Postgres DBs, different files, other DB implementations, etc. from within PostgreSQL