SEQUEL: A structured English query language
SIGFIDET '74 Proceedings of the 1974 ACM SIGFIDET (now SIGMOD) workshop on Data description, access and control
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Not all predicate calculus WFF correspond to meaningful questions, In order to avoid this problem, +different authors have defined syntactically the WFF classes which are known to be significative. These restrictions are generally more severe than is necessary, and we have defined a much wider class of WFF : the evaluable formula. We prove that these WFF have a clearly defined sense. Moreover, we can easily test a formula to see if it is evaluable. Finally, we show how it is possible to deduce from a formula the conditions which have to be fulfilled by the predicate argument validity domains in order to obtain-answers which are not an empty set. We can thus reject questions which have a defined sense but which, in the context of a clearly determined application, cannot have an answer.