Database - Data Modeling with ER Model - Discussion

Instance:
The combination of the system global area (SGA) and background processes. An instance is associated with one and only one database. In an Oracle Real Application Clusters configuration, multiple instances access a single database simultaneously.

SGA:
System global area. A group of shared memory structures that contain data and control information for one Oracle database instance.

Background process:
A process that consolidates functions that would otherwise be handled by multiple Oracle programs running for each client process. The background processes asynchronously perform I/O and monitor other Oracle processes.

It is because as the concept suggest one to many ie the ralationship from one (A) entity to other inherihed or deriver entities (B, C, D) to which we simply call as the child entities. Thats it.

Instances of a class have the same set of attributes.

However, each instance may be different because of what's inside each attribute.

Parent should be one and it has many child in one to many relation.

What is an instance?