Here, the parser starts with the S symbol and attempts to rewrite it into a sequence of terminal symbols that matches the classes of the words in the input sentence until it consists entirely of terminal symbols.
These are then checked with the input sentence to see if it matched. If not, the process is started over again with a different set of rules. This is repeated until a specific rule is found which describes the structure of the sentence.
Merit − It is simple to implement.
Demerits
● It is inefficient, as the search process has to be repeated if an error occurs.
● Slow speed of working.