The Access relationship represents the ability of behavior and active structure elements to observe or act upon passive structure elements.
The Access relationship indicates that a process, function, interaction, service, or event "does something" with a passive structure element; e.g., create a new object, read data from the object, write or modify the object data, or delete the object. The relationship can also be used to indicate that the object is just associated with the behaviour.
The arrow indicates the flow of information.
Create a new object, Read data from an object, Write or modify object data, Delete an object.
The “Create Invoice” sub-process writes/creates the “Invoice” business object; the “Send Invoice” sub-process reads that object