Query Languages Databases can contain enormous amounts of information. To get access to what we want, we need to do a database query. The query language allows one to specify report contents and formats. Query by example enables one to search a single table easily, by selecting which options per domain are acceptable. Structured query languages like SQL enable one to use relational operations to search multiple tables in complicated ways.
Project enables one to copy the specified domains instead of the entire tuple.
Join enables us to combine two relations, based on common fields. These three operations are very powerful, in the sense that you can express a wide variety of things, and further maps nicely to operations the database system can do. Many kinds of important information cannot be naturally encoded as text or numerical data. The latest database systems are begining to support non-text items. There is already a tremendous amount of geographic available on line.