ANSI/SPARC Architecture
Three-level mode structure + two-level image.
Level three mode refers to the
- External mode: A view of a single user, which is the data interface between the user and the database system. For a single user, the external mode is the database.
- Conceptual mode: Public view of all users, one database with only one conceptual mode .
- Internal mode: A storage view inside a database, which is a description of the physical structure and storage of the data. For example, the storage of records: Sequential storage, B-tree organization or hash storage, how the index is organized: sort or hash, whether the data is encrypted, whether the storage is compressed. a database has only one internal mode .
Secondary image refers to the
- External mode/Pattern Image: Defines the correspondence between the outside mode and the conceptual mode. Properties in the outer mode may be calculated by multiple attributes in the pattern. When the conceptual pattern changes, only the image can be modified to keep the external mode intact- the logical independence of the data .
- Mode/Internal mode image: Same. The physical independence of the data is embodied.
External architecture of the database system
- Single-User structure
- Master-Slave structure
- Distributed architecture
- Client/server architecture (c/s)
- Browser/server architecture
Review two--Database system architecture
