Inconsistent Databases
نویسنده
چکیده
SCIENTIFIC FUNDAMENTALS A database can be seen as a model, i.e. as a simplified, abstract description, of an external reality. In the case of relational databases, one starts by choosing certain predicates of a prescribed arity. The schema of the database consists of this set of predicates, possibly attributes, which can be seen as names for the arguments of the predicates, together with an indication of the domains where the attributes can take their values. Having chosen the schema, the representation of the external reality is given in terms of relations, which are extensions for the predicates in the schema. This set of relations is called an instance of the schema. For example, relational database for representing information about students of a university might be based on the schema consisting of the predicates Students(StNum,StName) and Enrollment(StName,Course). The attribute StNum is expected to take numerical values; StName, character string values; and Course, alphanumeric string values. In Figure 1 there is a possible instance for this schema.
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