Sigma QL Language Syntax

< query> ::= SELECT  < select_target>
            CLUSTER < cluster>
            FROM    < source>
            WHERE   < condition>

< select_target> ::= x | y | z | t | image_object |
                    audio_object | video_object | type

< cluster> ::=  * | < x_cluster> | < y_cluster> | < z_cluster> |
               < t_cluster>  

< x_cluster> ::=  < x_val> | < x_val> < x_cluster>

< x_val> ::= < val> | OPEN < val>

< source> ::= < query> | < source_name>

< condition> ::=  < string>