pattern matching

Pattern matching is when we have some sort of template or pattern which we are trying to find in data such as an image or document. Sometimes this is an exact match, such as locating names of places or people in a text (named entities). More often some form of fuzzy matching is required, for example, in a nosiy image. In both text and images the pattern may occur in different locations in the data, but in addition a pattern in an image may appear at different scales or rotations. The template may itself be expresed in a way that matches multiple things of similar structure, for example postal codes, using a pattern notation such as a regular expression.