Backus-Naur-Form

Start symbol: <sentence>,
Non-terminal symbols (non-terminals): <sentence>, <objective>, <predicate>; Terminal symbols (terminals): flowers, stars, bloom, shine; Metasymbols BNF notation : <, >, ::=, | Production rules – rules which allow to define a language. If we use single capital letters to denote non-terminal symbols and small letters to denote terminal symbols, the grammar from example 1 can be presented in the following way:

                                            
                                                
S::= AB
                                                
A::= x | y
                                                
B::= z | w

By applying the rule of consecutive replacements, a language sentence can be generated from the start symbol.

Method of sentence generating:

                                            
                                                
S→AB→xB→xw
                                                
S→AB→yB→yz <=> S→*yz
                                                
→* - indirect eduction


Such a way of deriving sentences from grammar is called top-down parsing. A language defined by this syntax allows for a derivation of four sentences: xz, yz, xw, yw.