Information Technology Reference
In-Depth Information
In order to propagate signals along a structure, there should be more than one
symbol on the left-hand side of a rule. In this case, the rules become
context-sensitive. In the following example, the symbol in “{ }” is the symbol
(or string of symbols) to be replaced, the rest of the left-hand side is the context,
and the symbols “[” and “]” indicate the left and right ends of the string,
respectively. Take the rule set as an example, which contains the following rules:
(1) [{C}
ŗ
C
a “C” at the left-end of the string remains a “C”.
(2) C{C}
ŗ
C
a “C” with a “C” to its left remains a “C”.
(3) *{C}
ŗ
*
a “C” with an “*” to its left becomes an “*”.
(4) {*}C
ŗ
C
an “*” with a “C” to its right becomes a “C”.
(5) {*}]
ŗ
*
an “*” at the right end of the string remains an “*”.
Under these rules, the “*” in the initial structure “*CCCCCCC” will be
propagated to the right as shown below:
The capability of signal propagation is extremely important, because it allows
any computational process to be embedded within the structure, which may
directly influence the structure's development.
time
structure
0
*CCCCCCC
1
C*CCCCCC
2
CC*CCCCC
3
CCC*CCCC
4
CCCC*CCC
5
CCCCC*CC
6
CCCCCC*C
7
CCCCCCC*
