Constraints are statements that is required to hold over the data.

In relationsal databases there are the standard relational constraints, such as types, PRIMARY KEY, REFERENCES, NOT NULL, UNIQUE and CHECK. For more complex constraints, one use more complex functionality such as triggers.

For triplestores and RDF one can use any of the constraint languages available, such as SHACL or SPIN, or use OWL to check for inconsitencies.

Relevant Articles and Tutorials

• For SQL-constraints, see the PostgreSQL page
• For links on SHACL, see the SHACL page
• For information on constraints in Lore, see the Lore page