- Dirty reads occur when:
- Transaction A inserts a row into a table.
- Transaction B reads the new row.
- Transaction A rolls back.
- Nonrepeatable reads occur when:
- Transaction A reads a row.
- Transaction B changes the row.
- Transaction A reads the same row a second time and gets the new results.
- Phantom reads occur when:
- Transaction A reads all rows that satisfy a WHERE clause on an SQL query.
- Transaction B inserts an additional row that satisfies the WHERE clause.
- Transaction A re-evaluates the WHERE condition and picks up the additional row.
UML - Association, Aggregation, Composition, Generalization, Specialization, Realization and Dependency
Association Association is a simple relationship between two classes. For example A relationship between Professor Class and Student class is known as Association. Both Classes can exist without each other, so Professor and Student are two independent classes. In this kind of relationships there will not be any owner class. Both classes have their own life cycle. UML Notation: Aggregation Aggregation is a special type of Association. It is known as “Has-A” relationship. For example A Department class can contain Professor Class. Here Department class is owner class. Here in this relationship even after deleting Department class, Professor Class can exits. UML Notation: Composition Composition is a special type of Aggregation. It is known as “Is-A” relationship. For example A University Class has many Department class. Here University and Department objects are dependent on each other. If we delete Univ...
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