preliminary definitions(cont¡¯d)
- Join dependency
- Let R be a relation, and let A, B, ¡¦, Z be arbitrary subsets of the set of attributes of R. Then we say that R satisfies the JD
- * ( A, B, ¡¦ , Z )
- iff R is equal to the join of its projections on A,B,¡¦Z.
- Anomaly
- a condition which interferes with the storage, or retention of data or creates the potential for inconsistent data.
- There are insertion, modification, and deletion anomalies.
- The normalization process should eliminate anomalies.