A concrete Boolean conjunctive query over variables and constants is a list of binary atoms with arguments in their disjoint union, and a concrete graph database a list of facts over the constants; the query holds in the database when some assignment of the variables to constants sends every atom to a fact. A packaged instance fixes the numbers of variables and of constants, at least one constant, with finite sets of atoms and of facts; its size is the textbook one, elements plus atoms plus facts. The encoder computes the structure of an instance, on its variables and constants as universe, and a concrete query and database give a structure on their disjoint union directly. A presentation is a raw relation table on a finite universe; an instance is well-formed when some element is a constant, which a first-order sentence states, and the decoder reads a packaged instance off a well-formed presented structure by numbering its variables and its constants in order. Well-formed evaluation is evaluation restricted to well-formed instances.