An implementation of inventory system for Lafene Health Center based on dbase III plus
Soudabeh. Farzbod · K-State Research Exchange (Kansas State University) · 1987
KeysA key is the attribute or set of attributes that uniquely identifies tuples in a relation.Each key has three properties for all time and for any instance of the relation.1. Uniqueness -The set of attributes takes on a unique value in the relation for each tuple.2. Nonredundancy -If an attribute is renamed from the set of attributes, the remaining attributes do not possess the uniqueness property.3. Validity -No attribute value in the key may be null .The relation key is often called the "candidate key."If a key is the only key of the relation, it is generally referred to as the "primary key." 4. Normal Form.With some relations, changing data (insertion, deletion, update) can have unexpected consequences.These consequences are called modification anomalies and they are not desirable.Relational schemes are normalized to incor- porate desirable properties in the data base.The two techniques of normalization are synthesis of the data base as proposed by Bernstein (1976) and by decomposition proposed by Codd.