MACM 101 Lecture 7: Lecture 7 Part 2_ Introduction Predicates and Quantifiers
21 Dec 2018
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Lecture 7 part 2: introduction predicates and quantifiers. We cannot assign a variable of a predicate any value. Every variable of a predicate is associated with a universe or universe of discourse, and its values are taken from this universe. A relational database is a collection of tables like. A table consists of a schema and an instance. A schema is a collection of attributes, where each attribute has an associated universe of possible values. An instance is a collection of rows, where each row is a mapping that associates with each attribute of the schema a value in its universe. Every table is a predicate that is true on the rows of the instance and false otherwise. One way to obtain a statement from a predicate is to assign all its variables some values. Another way to do that is to use expressions like. There is x such that x is greater than 3".
