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An illustration of properties of join algorithms. When performing a join between more than two relations on more than two attributes, binary join algorithms such as hash join operate over two relations at a time, and join them on all attributes in the join condition; worst-case optimal algorithms such as generic join operate on a single attribute at a time but join all the relations on this ...
If-then-else flow diagram A nested if–then–else flow diagram. In computer science, conditionals (that is, conditional statements, conditional expressions and conditional constructs) are programming language constructs that perform different computations or actions or return different values depending on the value of a Boolean expression, called a condition.
A constraint logic program is a logic program that contains constraints in the body of clauses. An example of a clause including a constraint is A (X, Y):-X + Y > 0, B (X), C (Y). In this clause, X + Y > 0 is a constraint; A(X,Y), B(X), and C(Y) are literals as in regular logic programming.
A clause is a disjunction of literals (or a single literal). A clause is called a Horn clause if it contains at most one positive literal. A formula is in conjunctive normal form (CNF) if it is a conjunction of clauses (or a single clause). For example, x 1 is a positive literal, ¬x 2 is a negative literal, and x 1 ∨ ¬x 2 is a clause.
This is an example of mathematical jargon (although, as noted above, if is more often used than iff in statements of definition). The elements of X are all and only the elements of Y means: "For any z in the domain of discourse , z is in X if and only if z is in Y ."
Python supports conditional execution of code depending on whether a loop was exited early (with a break statement) or not by using an else-clause with the loop. For example, For example, for n in set_of_numbers : if isprime ( n ): print ( "Set contains a prime number" ) break else : print ( "Set did not contain any prime numbers" )
Python. The use of the triple-quotes to comment-out lines of source, does not actually form a comment. [19] The enclosed text becomes a string literal, which Python usually ignores (except when it is the first statement in the body of a module, class or function; see docstring). Elixir
A Datalog program consists of a list of rules (Horn clauses). [1] If constant and variable are two countable sets of constants and variables respectively and relation is a countable set of predicate symbols , then the following BNF grammar expresses the structure of a Datalog program: