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Building Parsers with Java™ by Steven John Metsker

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12.2. The Role of Engines

Some languages rely on an engine to perform a useful service. In particular, logic languages and query languages need an engine in order to work. For example, Prolog is a leading logic programming language that needs an engine to prove its logical statements. SQL, or Structured Query Language, is a popular query language that also uses an engine to do the work that a query requests. A parser can parse a statement such as:

"select status from sales where city = 'Istanbul'" 

However, a parser needs an engine to actually find the results. The engine is the part of the software in a database that decides which records fulfill the demands of a query.

Writing code to directly access an engine is usually complicated. It is ...

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