So far we have seen how to move from unstructured information to structured information. In particular, we have learned that this operation requires a lot of resources. The need for properly structured data derives from the need to search for information in a database to extract knowledge.
Any Database management system (DBMS) provides a very powerful tool for consulting the contents of database tables: queries.
A DBMS, is a software system designed to allow the creation, manipulation (by a DBA administrator) and the efficient query (by one or more client users) of databases, so also called a database manager or an engine, and hosted on a dedicated hardware architecture (server) or on a simple computer.
A query is a method for querying the database, that is, to display information extracted from the tables. For this purpose it is possible to perform several...
