BCS has been in use since SharePoint 2010. If you previously used BCS in SharePoint 2010, you'll feel right at home. As noted before, BCS enables us to connect to external data sources and display the data via web parts, lists, user profile properties, or search.
When discussing BCS we need to understand that BCS is not a technology by itself. It is a grouping term for a set of technologies, which takes care of getting the data from the external system. An external system can be anything from databases (such as SQL server or Oracle) to web services, and even cloud-based solutions.
BCS uses the connectors framework to reach out to external systems. Out of the box, we have four types of connectors we can use straight away: SQL, WCF, .NET, and the newly added OData connector. While the Business Data Connectivity (BDC) layer is in charge of connecting the external system, it does not know or dictate what data will be returned from the system, or what would its schema look like....