Week 2

2.3 Data Independence

Data independence is the ability to change the schema at one level without affecting the schema at the next higher level. There are two types:

Type	Definition and Example
Physical Data Independence	The ability to change the physical (internal) schema without affecting the conceptual schema. Example: Moving the bank's database from HDD to SSD storage, or changing the indexing strategy, without any change to the table structures or applications.
Logical Data Independence	The ability to change the conceptual (logical) schema without affecting the external schema or applications. Example: Adding a new column to a Customer table without breaking existing applications that do not use that column.