Graph descriptions or graph constraints are (restricted) Boolean expressions over node relations and node descriptions. Currently, conjunction & and disjunction | are available as logical connectives. For example, with the help of the &-operator, the following node relations can be joined into a graph constraint which retrieves the tree shown below.
(#n1 >SB #n2) & (#n1 >HD #n3) & (#n2 >NK #n4) & (#n2 >NK #n5)
Parentheses can be omitted in the usual fashion:
#n1 >SB #n2 & #n1 >HD #n3 & #n2 >NK #n4 & #n2 >NK #n5
The operator precedence is defined as follows: Relation, &, |. This definition is illustrated by the following examples:
Example | Interpretation |
#v > #w & #x | (#v > #w) & #x |
#v & #w | #x | (#v & #w) | #x |