DBMS Architecture

Three-Schema (ANSI/SPARC) Architecture

External levelConceptual levelInternal levelView 1View 2View 3Conceptual schema — tables, relationships, constraintsInternal schema — files, indexes, storage structuresStored data↕ logical data independence↕ physical data independence
ANSI/SPARC three-schema architecture

Data Independence

TypeMeaningExample
Logical data independenceChange the conceptual schema without changing external views or applicationsAdding a new column
Physical data independenceChange internal storage without changing the conceptual schemaAdding an index, moving to SSD
Exam pointPhysical independence is easier to achieve than logical independence.

1-tier, 2-tier and 3-tier Architecture

  • 1-tier: user works directly on the DBMS.
  • 2-tier: client application ↔ database server (e.g. via ODBC/JDBC).
  • 3-tier: client ↔ application server ↔ database server. This is how most web apps work.

Data Models

Hierarchical, network, relational (tables, the most common), entity-relationship, object-oriented and NoSQL models (document, key-value, graph, column-family).

Track your progress through the DBMS course