An optional block can contain any graph pattern, not just a single triple as shown in Listing 6.
可选块可以包含任何图形模式，不仅仅是像清单6所示的那种单一的三元模式。
2
Optional blocks can also be nested, in which case the inner optional block is only considered when the outer optional block's pattern matches the graph.
可选块也可以嵌套，在这种情况下，只有外部可选块的模式与图形匹配时，才考虑内部可选块。
3
Edges in the graph represent flow of control from one statement (or block) to another.