The search for the best strategy must not yet be concluded when , for example, the following conditions apply at the same time:
- The sequential search is the best strategy.
- There are search conditions combined by OR.
The conditions combined by OR which have not yet been considered are analyzed in order to find strategies better than the sequential search.
The procedure is as follows:
- The search condition is transformed into the disjunctive normal form.
Example:
b1 and b2 and (b3 or b4 and b5)
=
(b1 and b2 and b3)
or
(b1 and b2 and b4 and b5)
- Analysis of the new expression:
Every subexpression is analyzed separately. If the result of this analysis is the sequential search through the complete table, then this is the only applicable strategy. If the analysis gives a better search strategy for every subexpression, there are generally as many strategies as subexpressions that have been analyzed.
- Cost-finding:
The costs of the different strategies are added up. If the total is less than the cost of the sequential search, the different strategies are applied.