variety of formal systems have branched out from what is abstractly the same formal base of graph-theoretic structures. Conceptual graph A conceptual graph (CG) is a notation for logic based on the existential graphs of Charles Sanders Peirce and the semantic networks of artificial intelligence. In the first published paper on conceptual graphs, John F. Sowa used them to represent the conceptual schemas used in database systems. His first book applied them to a wide range of topics in artificial intelligence, computer science, and cognitive science. A linear notation, called the Conceptual Graph Interchange Format (CGIF), has been standardized in the ISO standard for Common Logic. The diagram on the right is an example of the display form for a conceptual graph. Each box is called a concept node, and each oval is called a relation node. In CGIF, this CG would be represented by the following statement: [Cat Elsie] [Sitting *x] [Mat *y] (agent ?x Elsie) (location ?x ?y) In CGIF, brackets enclose the information inside the concept nodes, and parentheses enclose the information inside the relation nodes. The letters x and y, which are called coreference labels, show how the concept and relation nodes are connected. In the Common Logic Interchange Format (CLIF), those letters are mapped to variables, as in the following statement: (exists ((x Sitting) (y Mat)) (and (Cat Elsie) (agent x Elsie) (location x y))) As this example shows, the asterisks on the coreference labels *x and *y in CGIF map to existentially quantified variables in CLIF, and the question marks on ?x and ?y map to bound variables in CLIF. A universal quantifier, represented @every*z in CGIF, would be represented forall (z) in CLIF. Entitative graph An entitative graph is an element of the graphical syntax for logic that Charles Sanders Peirce developed under the name of qualitative logic beginning in the 1880s, taking the coverage of the formalism only as far as the propositional or sentential aspects of logic are concerned. The syntax is: The blank page; Single letters, phrases; Objects (subgraphs) enclosed by a simple closed curve called a cut. A cut can be empty. The semantics are: The blank page denotes False; Letters, phrases, subgraphs, and entire graphs can be True''' or False; To surround objects with a cut is equivalent to Boolean complementation. Hence an empty cut denotes Truth; All objects within a given cut are tacitly joined by disjunction.