Query language representations of constraints useable to cause query failure

A method, implemented in a computing system comprising at least one hardware processor and at least one memory coupled to the at least one hardware processor, the method comprising:

• at a federated database system, receiving a first query comprising a first query expression comprising a first plurality of query operations specified in a first query language from a source database system, the first plurality of query operations comprising a first query operation expressing a constraint, the first query operation being a keyword of the first query language, wherein the keyword provides that, during query execution of the first plurality of query operations at the federated database system, when the constraint associated with the keyword is not satisfied, query execution of a query plan generated from the first query expression generates a failure result and no logical answer to the query is produced;
• from the first query expression, generating a query plan, the query plan comprising an operation to evaluate the constraint;
• executing the query plan;
• evaluating the constraint during execution of the query plan;
• and
• when the constraint is satisfied, providing an execution result of executing the query plan to the source database system as a result of the first query, or, when the constraint is not satisfied, providing the failure notification to the source database system.

One or more computer readable storage media comprising:

• computer-executable instructions that, when executed by a computing system comprising at least one hardware processor and at least one memory coupled to the at least one hardware processor, cause the computing system to, at a first database system, receive or generate a first query comprising a first query expression comprising one or more query operations specified in a first query language, a first query operation of the one or more query operations being a keyword in the first query language and expressing a constraint, wherein query execution of a query plan implementing the constraint is terminated if the constraint is not satisfied, and the first query expression returns a failure result and no logical answer to the first query expression is produced;
• computer-executable instructions that, when executed by the computing system, cause the computing system to cause a first query plan generated using the first query expression to be executed;
• computer-executable instructions that, when executed by the computing system, cause the computing system to, during execution of the first query plan, determine that the constraint is not satisfied;
• and
• computer-executable instructions that, when executed by the computing system, cause the computing system to, based on determining that the constraint is not satisfied, cause execution of the first query plan to generate the failure result.