In reply to papatel:
Yes a sequence item is a class. But it is a transient obejct. This will be cerated at any time and destroyed after ist has been processed.
A sequence is an extension of the seq_item. It is also transient. It describes how the sequence items will be generated.
A sequence and the test are completely different things. A test is a component object. It is created at runtime 0 and exists until the simulation hes been finished. In the test you can start 1 or more sequences. A component belongs to the testbench topology.