Information Technology Reference
In-Depth Information
about Negative Selection Algorithm (NSA) [11, 12] have been done [13-16], and some
of them can be applied to solve the self-tolerant problem. D'haeseleer proposed a
method for counting the number of holes, and presented a greedy algorithm that
attempts to reduce the size of the detector set [13]. Zhou and Dasgupata proposed an
NSA with variable-coverage detectors in real-valued space [14, 15]. Zhang et al.
presented the r-Adjustable NSA in binary string space [16], etc. However, with
methods in [13-16], the problem with holes can be only partially avoided by
non-autoimmune systems in static environments. Furthermore, in dynamic
environments, the self set could change. Therefore, apart from the detector set
generation algorithms, the detector set updating strategy is very important for the
application of NSA in dynamic environments, and it is a key issue for the self-tolerant
problem.
Aiming at the self-tolerant problem in dynamic environments (in which the self set
will grow during detection), two detector set updating strategies are proposed in this
paper. One of them is inspired by the variable matching length mechanism [14-16], the
other just removes the self pattern by stuffing some bits of detector with special
symbols. These two novel strategies are compared with the works in [8] and [9].
Results of emulation experiments show that the detector sets being updated by the new
strategies are less affected by the growing of the self set, and have a better coverage on
the non-self space.
Section 2 briefly introduces the self-tolerant problem and some efforts already made
by researchers. Two novel detector set updating strategies are described in detail in
section 3. Section 4 is devoted to demonstrating the simulation experimental results.
Discussions are given in section 5. Conclusions and future works are given in section 6.
2 Self-tolerance Problem of HIS in Dynamic Environments
Generally the biological immune system is tolerant of the self, i.e. it does not attack the
self. But a small quantity of lymphocytes may bind to self and the body will be attacked
by the immune system, this response is called autoimmunization. In general, all
lymphocytes will suffer the process of negative selection. However, there are still some
lymphocytes matching the self released to the blood circulation. The peripheral
self-tolerance can be dynamically maintained by a mechanism called co-stimulation.
For example, B-cells can be activated only when they receive the first signal from
captured pathogens and the second signal from lymphocytes called helper T-cells in the
same time. The helper T-cells will provide second signal only if they recognizes the
pathogens captured by B-cells as non-self. [17]
In hardware immune systems, if the known self set (the set of known valid state
transitions) is incomplete, after the filtration process of the detector set, some detectors
may recognize unknown valid state transitions as non-self (invalid state transitions) and
give a wrong alarm (a false positive). A co-stimulation mechanism has been developed
to maintain the tolerance of self [8, 9].
Self-tolerant problem is an essential issue in both biological immune systems and
hardware immune systems under dynamic environments. When the self set grows, the
