The major contrast between unstructured and structured search is the items we are trying to categorize and index. Traditionally, structured search tools fall into the domain of database technology. The easiest way to think of structured information is something one could put in a table. In setting up the database, the user would specify the dimensions and the data types of each dimension.
Most databases provide a number of different data types for indexing.
These can include, strings, characters, real numbers, integers, and esoteric multimedia and BLOB types. Another way to look at structured search applications is in terms of metadata . Metadata, for our purposes, are information about information. Because databases understand data types, it is possible to formulate powerful queries on information other than text. While it was possible to test cetain mathematical predicates, most databases are incapable of judging between the semantic similarity of two items.