Some of the most common types
of search algorithms include the following:
■ List search: A list-search algorithm searches through specified data looking for a single
key. The data is searched in a very linear, list-style method. The result of a list search is
usually a single element, which means that searching through billions of web sites could
be very time-consuming, but yields a smaller search result.
■ Tree search: Envision a tree. Now examine that tree either from the roots out or from
the leaves in. This is how a tree-search algorithm works. The algorithm searches a data set
from either the broadest to the most narrow or from the most narrow to the broadest. Data
sets are like trees: A single piece of data can branch to many other pieces of data, which is
very much how the Web is set up. Tree searches, then, are more useful when conducting
searches on the Web, although they are not the only searches that can be successful.
■ SQL search: One of the difficulties with a tree search is that it is conducted in a hierarchical
manner, meaning it’s conducted from one point to another, according to the ranking of
the data being searched. A SQL (pronounced see-quel) search enables data to be searched
in a nonhierarchical manner, which means that data can be searched from any subset
of data.
■ Informed search: An informed-search algorithm looks for a specific answer to a specific
problem in a tree-like data set. The informed search, despite its name, is not always the
best choice for web searches because of the general nature of the answers being sought.
Instead, informed search is better used for specific queries in specific data sets.
■ Adversarial search: An adversarial-search algorithm looks for all possible solutions to a
problem, much like finding all the possible solutions in a game. This algorithm is difficult
to use with web searches because the number of possible solutions to a word or phrase
search is nearly infinite on the Web.
■ Constraint satisfaction search: When you think of searching the Web for a word or
phrase, the constraint-satisfaction-search algorithm is most likely to satisfy your need to
find something. In this type of search algorithm, the solution is discovered by meeting
a set of constraints, and the data set can be searched in a variety of different ways that
do not have to be linear. Constraint satisfaction searches can be very useful for searching
the Web.