Here's a breakdown:
* Direct Dependency: A table directly depends on another table if it contains a foreign key that references the primary key of the other table. For example, an "Orders" table might have a foreign key referencing the "Customers" table.
* Transitive Dependency: When a table depends on another table that itself depends on a third table, it's called a transitive dependency. Imagine a scenario where the "Orders" table has a foreign key referencing the "Customers" table, and the "Customers" table has a foreign key referencing a "Regions" table. In this case, the "Orders" table has a transitive dependency on the "Regions" table.
Consequences of Transitive Dependency:
* Data Redundancy: Data related to the third table (e.g., region information) is duplicated across multiple records in the second table.
* Update Anomalies: Changes to the third table require updates in both the second and first tables, increasing the risk of inconsistencies.
* Insertion Anomalies: You cannot insert a record into the first table without a corresponding record in both the second and third tables.
* Deletion Anomalies: Deleting a record in the third table can cause inconsistencies and potential data loss in the first and second tables.
* Performance Issues: Queries involving transitive dependencies can be complex and inefficient.
Normalization and Transitive Dependencies:
The goal of database normalization is to eliminate these issues by removing transitive dependencies. This is typically achieved by splitting the original table with the transitive dependency into two tables, one directly related to the third table and the other with the direct relationship to the first table.
Example:
Let's consider a simple example with the tables mentioned above:
* Orders: (OrderID, CustomerID, OrderDate, ... )
* Customers: (CustomerID, CustomerName, RegionID, ... )
* Regions: (RegionID, RegionName, ...)
Here, "Orders" has a transitive dependency on "Regions" through "Customers." To normalize, you could create a new table:
* CustomerRegions: (CustomerID, RegionID)
This new table eliminates the transitive dependency. Now, "Orders" depends directly on "Customers," and "Customers" depends directly on "CustomerRegions," which, in turn, depends on "Regions."
In summary:
Transitive dependencies are undesirable in database design. They lead to data redundancy, update anomalies, and potential performance problems. Database normalization techniques are employed to eliminate these dependencies and ensure data integrity and efficiency.