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Update Anomalies and Normalization
In the database world “update” is a very famous word, one that can make people swallow some saliva in some instances (evil laugh here) . Update anomalies is one of the many computer science paradigms,...
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In the database world the lines that connect the different entities (tables) together are called relationships; these are the relationships that occur in real life between entities as part of a...
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Anatomy of a database relationship
Every relationship is said to have cardinality. The cardinality is the degree of the relationship. There are two types of degrees: Optionality: Is the minimum degree of the relationship and it can be...
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One-to-One Relationships
A One-to-One relationship is a binary relationship. It occurs when one record in one entity references one record in the second entity. Some modelers suggest that One-to-One relationships should be...
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One-to-Many Relationships
A One-to-Many relationship occurs when an entity can have multiple instances of another entity in a relationship. The cardinality of the relationship between the two entities will dictate the number of...
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Many-to-Many Relationships
This topic deserves special attention because many people from database designers to application developers (sometimes one person does both) do not get it right. A Many-to-Many relationship occurs when...
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Self-Referencing relationships
Also known as recursive relationships, these are unary type relationships. These type of relationships occur when an entity can reference itself. Recursive relationships occur often in hierarchies, and...
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Database Inheritance : Subtyping
If you are familiar with any object oriented programming language, the term inheritance may not be new to you. In OO programming such as in Java or C++ you basically put all the common attributes and...
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