The database is a data set that can be stored together in a certain way, shared by multiple users, with as little redundancy as possible, and independent of the application program. It can add, intercept, update and delete data in files.

Type:

relational database
Non relational database

database model
object model
Hierarchical model (lightweight data access protocol)
Mesh model (large data storage)
relational model
Object oriented model
Semi structured model
The planar model (table model is generally a two-dimensional array in form).

Framework:
The architecture of database can be roughly divided into three general levels: inner level, conceptual level and outer level.            Inner layer: nearest to the actual memory, that is, the actual storage mode of the data.
Outer layer: closest to users, that is, the way users view data.

Conceptual level: an indirect layer between them.

Database index:
Indexes have a corresponding relationship with fields. Indexes are derived from fields, in which fields have so-called key fields, which have uniqueness, that is, their values are not repeatable and can not be "null".