Recently in the design database (
NySQLI borrowed a book and saw it in it
Three-level mode structureAnd
Two-level mapping mechanismThese words, Baidu also checked the explanation of these two words, but it is still not clear how to realize these words, instead of simply making an explanation.
Although everyone has a different understanding of this, there is no complete answer. However, I still hope that everyone can talk about their own views and tell us beginners about them.
How is the three-level schema structure and two-level mapping mechanism of the database system implemented in MySQL?;
I am also a student, and I am also studying the database. My understanding is:
Three-level mode structure:
- External mode: user mode, which is the combination of the final data seen by the user, is processed and packaged. The implementation can be realized through the view of the database, and different users of the same set of data will have different views.
- Pattern: It is the logical relation of tables in the database. The logical relation of these data is an abstraction from the real world. These definitions have certain constraints, which are specified and implemented by the database management system.
- Internal schema: a description of how the database system converts from schema to storage on a physical device, which defines whether storage is encrypted and according to what data structure. Is managed by a database management system dbms
I am not very clear about the two-level image. I am looking forward to other people’s answers.