In large applications, it is fairly common to have name collisions. One developer might create an Employee class, while another makes a function named Employee that returns the employee ID for a particular person's name. Or two developers might build different Employee classes that have different properties and different purposes. When multiple items have the same name, this is called a namespace collision or namespace pollution.
These sorts of name conflicts are most common when programmers are not working closely together. For example, different developers working on the payroll and human resources systems might both define Employee classes with slightly different purposes.
Namespaces enable you to classify and distinguish among programming entities that have the same name. For example, you might build the payroll system in the Payroll namespace and the human resources system in the HumanResources namespace. Then, the two Employee classes would have the fully qualified names Payroll.Employee and HumanResources.Employee, so they could coexist peacefully and the program could tell them apart.
The following code shows how an application would declare these two types of Employee objects:
Dim payroll_emp As Payroll.Employee Dim hr_emp As HumanResources.Employee
Namespaces can contain other namespaces, so you can build a hierarchical structure that groups different entities. You can divide the Payroll namespace into pieces to give developers working on that project ...