1. A system for planning and generating database queries using a multitude of data sources in various formats and media, which enables multi-dimensional analyses without physically building a data warehouse, the system comprising: a memory; a domain model which provides a formal description of a domain of interest, comprising classes which are concepts in a domain of discourse, properties of each class describing its attributes including its relations with other classes and constraints on properties in the classes; a mapping server which generates a domain model specific to a set of data sources by specifying mapping between entities in said domain model and entities in the data sources; an ontology query generator which translates one or more queries in a natural language format to generate one or more ontology queries which can be understood in terms of said domain model; an ontology query server which infers one or more answers to ontology queries by reasoning with said domain model; a SQL query plan generator which composes one or more query plans using a standard query language for relational databases for multi-dimensional analysis including one or more of data grouping, roll-up and drill-down, pivoting, and changing the focused class of the current multi-dimensional analysis; a data federation system which builds one or more adaptors for individual data sources which make data sources appear as relational databases and allow them to be accessed by using a standard query language for relational databases and which also optimizes query plans for performance and processes queries to retrieve data from one or more data sources; and a report generator which provides data retrieved from data sources for multi-dimensional analysis.