Transfer Operations

Transfer operations are operations that involve (or can be derived from) moving, copying, and linking objects from one location to another. For example, printing an object is a form of a transfer operation because it can be defined as copying an object to a printer.

Three components make up a transfer operation: the object to be transferred, the destination of the transfer, and the operation to be performed. You can define these components either explicitly or implicitly, depending on which interaction technique you use.

The operation defined by a transfer is determined by the destination. Because a transfer may have several possible interpretations, you can define a default operation and other optimal operations, based on information provided by the source of the transfer and the compatibility and capabilities of the destination. For example, attempting to transfer an object to a container can result in one of the following alternatives:

Rejecting the object.
Accepting the object.
Accepting a subset or transformed form of the object (for example, extract its content or properties but discard its present containment, or convert the object into a new type).

Most transfers are based on one of the following three fundamental operations.

Operation	Description
Move	Relocates or repositions the selected object. Because it does not change the basic identity of an object, a move operation is not the same as copying an object and deleting the original.
Copy	Makes a duplicate of an object. The resulting object is independent of its original. Duplication does not always produce an identical clone. Some of the properties of a duplicated object may be different from the original. For example, copying an object may result in a different name or creation date. Similarly, if some component of the object restricts copying, then only the unrestricted elements may be copied.
Link	Creates a connection between two objects. The result is usually an object in the destination that provides access to the original.

There are two different methods for supporting the basic transfer interface: the command method and the direct manipulation method.