A Model of Gene Library Evolution in the Dynamic Cl onal Selection Algorithm

The dynamic clonal selection algorithm (dynamiCS) was created to tackle the difficulties of anomaly detection in continuously changing environments (Kim and Bentley, 2002a). This algorithm was extended in a sister paper (Kim and Bentley, 2002b), so that memory detectors that are no longer valid are automatically deleted. Here we describe a further extension to the system: the use of hypermutation on deleted memory detectors to produce, in effect, a " virtual gene library " which seeds the immature detector population. When using an Artificial Immune System (AIS) in a r eal environment (e.g., monitoring network traffic), nor mal or self behaviours can change after a certain period. In addition, the system may only see a small subset of self antigens at any one time. In order for our AIS to be able to deal with such an environment, a dynamic clonal selectionalgorithm(DynamiCS)wasintroducedin previous work (Kim and Bentley, 2002a). The results described there showed that DynamiCS could incrementally learn the globally converged distribu tions even though only one subset distribution was given at each generation. This feature was achieved by emplo ying three important parameters: tolerisation period of an immature detector (T), activation threshold of a mature detector (A) and the life span of a mature detector. However, the original DynamiCS could not learn new self-antigens when learned self and non-self behavi ours suddenly altered due to legal self change. This res ulted in high false positive (FP) rates when new antigens we re monitored by DynamiCS, although it produced high tr ue positive (TP) rates. A sister paper to this describes a further extensio n of DynamiCS, which reduces FP rates increased by memor y detectors (Kim and Bentley 2002b). The extended DynamiCS handles generated memory detectors based o n their detection results. The original DynamiCS pres erved memory detectors for an infinite lifespan. In contr ast, the extended DynamiCS kills memory detectors if they sh ow poor self-tolerance to new antigens (Kim and Bentle y 2002b). This extended system was tested to determin e whether surviving memory detectors no longer cause seriously high FP error rates or not. From this tes t, it was analysed to see whether any other problems occur as a consequence of killing memory detectors. The analys is showed that the extended DynamiCS requires a larger amount of co-stimulation if it yielded high TP rate s. This analysis led to the work described in this …