URI normalization

URI normalization is the process by which URIs are modified and standardized in a consistent manner. The goal of the normalization process is to transform a URI into a normalized URI so it is possible to determine if two syntactically different URIs may be equivalent.
Search engines employ URI normalization in order to and to reduce indexing of duplicate pages. Web crawlers perform URI normalization in order to avoid crawling the same resource more than once. Web browsers may perform normalization to determine if a link has been visited or to determine if a page has been cached.
Normalization process.
There are several types of normalization that may be performed. Some of them are always semantics preserving and some may not be.
Normalizations that preserve semantics.
The following normalizations are described in RFC 3986 to result in equivalent URIs:
Normalizations that usually preserve semantics.
For http and https URIs, the following normalizations listed in RFC 3986 may result in equivalent URIs, but are not guaranteed to by the standards:
Normalizations that change semantics.
Applying the following normalizations result in a semantically different URI although it may refer to the same resource:
Normalization based on URI lists.
Some normalization rules may be developed for specific websites by examining URI lists obtained from previous crawls or web server logs. For example, if the URI
appears in a crawl log several times along with
we may assume that the two URIs are equivalent and can be normalized to one of the URI forms.
Schonfeld et al. (2006) present a heuristic called DustBuster for detecting DUST (different URIs with similar text) rules that can be applied to URI lists. They showed that once the correct DUST rules were found and applied with a normalization algorithm, they were able to find up to 68% of the redundant URIs in a URI list.