Rule format:

s -> np vp

The left side of the above rule stands for a sentence while the right side means a sentence consists of a Noun Phrase and a Verb Phrase. This kind of rules are called context-free rewrite rules.

Syntactic structure format

[S1 [NP The/DT dog/NN][VP runs/VBZ]]

S1 stands for the first successful application of the rule s-> np vp.
Each pair of square brackets form a syntactic constituent. The including relations among square brackets represent the phrase struture of the sentence.
As in the tagger, the slash introduce the part of speech of every word.