ERROL (an acronym for Entity Relationship Role Oriented Language; Markowitz and Raz 1983a) is a declarative database query and manipulation language for the Entity-relationship model (ERM). It is applicable to any data model on which ERM can be mapped, virtually any general purpose database data model. It is based on the capability of ER diagrams to be described accurately by simple Natural language (NL) sentences. A specification of a complex operation upon an ERM database can be described accurately by a complex and/or compound NL sentence constructed from the simple sentences describing the respective ER diagram. An ERROL expression mimics such NL sentence with one-to-one correspondence between ERROL subexpressions and NL subsentences: An ERROL expression can look like the corresponding NL sentence, or at least like a similar, equivalent one. This allows to write in ERROL very complex queries by simple conversion from their NL specifications. It also allows a straightforward checking of an ERROL expression meeting a complex NL specification. With such characteristics it can be a foundation for future Data management languages, more convenient to use than existing languages which may need complex expressions even for moderately complex NL expressions (e.g., SQL; see Example below).

ERROL is also applicable to newer applications like querying the Semantic web using ontologies.

Reshaped Relational Algebra (RRA; Markowitz and Raz 1983b, 1984), with operators that follow the semantics of respective major NL constructs, has been developed to support ERROL over relational databases. It is used both to specify ERROL's semantics concisely and accurately, and to implement ERROL effectively over relational databases.

ERROL and its RRA translation expose and exploit the connection between the way we reason and talk about needed information, possibly very complex, and the database operations needed in order to compute this information from the database data. A sequence of such RRA operations is generated automatically from an ERROL expression by an ERROL-to-RRA compiler. The compiler output has been applied directly to a relational database, and also has a translation to SQL, the standard interface, for a straightforward, "regular" execution by SQL database systems.

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