BMGT 402 Lecture Notes - Lecture 4: Dno, Referential Integrity, Minit Records

• School: University of Maryland
• Department: Business and Management
• Course: BMGT 402
• Professor: Woei- Jyh Lee

Document Summary

Bmgt402 lecture 4 chapter 4: relational model continued. Represents value for an attribute that is currently unknown or not applicable for tuple. Represents the absence or a value and is not the same as zero spaces, which are values: entity integrity. In a base relation, no value of a primary key can be null: referential integrity. If a foreign key exists in a relation, either foreign key value must match a candidate key value of some tuple in its home relation or foreign key value must be wholly null: general constraints. Additional rules specified by users or database administrators that define or constrain some aspect of the enterprise. Practical analysis of constraints: unique clientno cr74, entity integrity null, referential integrity b001 branchno, null foreign key can be inputted where the branch is to show that it hasn"t been assigned yet. Name relation corresponding to an entity in conceptual schema, whose tuples are physically stored in a database: view.