Grammar String

To illustrate the linking requirements, the following diagram shows a simple dictionary. The linking requirement of each word is represented by the diagram above the word.

Each shaped label box is a connector. Exactly one and only one of the connector attached to a given black dot must be satisfied. Thus, cat requires a D connector to its left, and either an O connector to its left or an S connector to its right.

The following diagram shows how the linking requirements are satisfied in the sentence The cat chased a snake.

** The unused connectors have been suppressed here **

It is easy to see that Mary chased the cat and The cat ran are sentences of this grammar. The sequence of words The Mary chased cat is not in this grammar, as shown by this diagram.

For succinctness, the following notation to represent links. The grammar that follows is equivalent to the above pictorial representation of the grammar.

a, the	D+
snake, cat	D- & (O- | S+)
Mary	O- | S+
ran	S-
chased	S- & O+

The linking requirement for each word is expressed in a expression involving the following operators:

&	the left and right expressions must evaluate true
|	either left or right expressions must evaluate true, but not both
@	indicates the link may accept multiple connections
( )	group expressions
[ ]	makes the expression optional

The + or - suffix on a connector name indicates the direction (relative to the word being defined) in which the matching connector (if any) must lie. The order of the expressions of an & is significant. The farther left a connector is in the expression, the nearer the word to which it connects must be. Thus, when using cat as an object (using an O- connector), its determiner (using a D- connector) must be closer than the verb.