The Oracle Open Gateway product set (previously called SQL*Connect) is used to access data from non-Oracle databases (eg. DB/2, Sybase, Informix, etc), and even non-relational data sources like Adabas and file systems.
Oracle Open Gateways can be divided into 4 categories:
Transparent Gateways
Procedural Gateways
Access Managers
Oracle Replication Servers
Transparent Gateways are most commonly used and enable access to non-Oracle data sources as if they were Oracle databases. They allow you to interact with these foreign databases without regard to differences in SQL implementation and with the added ability to perform distributed processing.
Procedural Gateways are used to integrate with non-ralational data sources. Normally a toolkit is used to map foreign database functions to PL/SQL stored procedures. These PL/SQL procedures can be called from any Oracle product like Oracle Forms and SQL*Plus.
Access Managers are exclusively used on IBM's AS/400 and MVS platforms and allows products like CICS to interact with Oracle and other IBM data sources like IMS. Look at the Oracle/MVS FAQ for more info.
Replication Servers support heterogenious data replication. For Oracle to Oracle replication, see the Oracle Replication FAQ.
