Diversity and Multi-Version Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 223

The S 3 strategy is characterized by some free-
dom “inside” of FPGA technology. In this case,
there are no restrictions for selection any FPGA-
based RTS either SRAM or Flash.
The S 4 strategy is characterized by some free-
dom “inside” of FPGA SRAM (Flash) technology.
In this case, the second RTS could be selected
from FPGA SRAM (Flash) families.
The S 5 strategy is characterized by freedom
“inside” of one family of FPGA SRAM (Flash)
technology. In this case, the second RTS could
be selected from one of family of FPGA SRAM
(Flash) families.
Generally, each S i diversity strategy includes
the subset of diversity strategies S ij , where j - a
number of possible alternatives classified as a
type of S i strategy. For example, different types
of S 3 might be the following strategies: S 31 - the
primary RTS - FPGA SRAM - based RTS (Stratix
IV (E,GX,GT)) and the secondary RTS - FPGA
FLASH-based RTS (XC3000), S 32 - the primary
RTS - FPGA SRAM - based RTS (Stratix IV
(E,GX,GT)) and the secondary RTS - FPGA
Flash-based RTS (XC4000), S 33 - the primary

RTS - FPGA SRAM - based RTS (Stratix IV
(E,GX,GT)) and the secondary RTS - FPGA
Flash-based RTS (Virtex), etc.
The hierarchy of diversity strategies is shown
on Figure 36.
The stages of RTS diversity assessment: The
linguistic approach for selection of the most diverse
RTS (Zadeh, 1999) deals with qualitative aspects
that are represented in qualitative terms by means
of linguistic variables. When a problem is solved
using linguistic information, it implies the need
for computing with the words (CW) (Zadeh, 1999).
Since CW deals with words or sentences defined
in a natural or artificial language instead of num-
bers, it emulates human cognitive processes to
improve solving processes of problems dealing
with uncertainty. Consequently, CW has been
applied as a computational basis to linguistic
decision making, because it provides tools close
to human beings reasoning processes related to
decision making, which improve the resolution
of decision making under uncertainty as linguis-
tic decision making. CW is an approximate tech-
nique in its essence, which represents qualitative

Figure 36. The hierarchy of diversity strategies