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Building Parsers with Java™ by Steven John Metsker

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15.1. The Role of Query Languages

Query languages, particularly SQL (Structured Query Language), represent a powerful force in applied computer science. Few businesses operate without a database, and every commercial database includes some form of a query language for retrieving data. The basic idea of SQL is that a query language empowers users to pose questions about data that no developer has foreseen. When you develop your own query language, you provide your users with this ability. Users of your language can derive new results without writing Java, and indeed without feeling as if they are “programming” at all.

The object that makes query languages possible is an engine. An engine knows how to answer a query, and it knows how to look through ...

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