Attaching a Conditional Expression
You can attach a conditional expression to each selection node on the tree path. The condition can be based on the values of any of the child nodes of the selection node. The expression syntax is based on the SQL conditions. For example, a condition attached to the 'employee' node of the 'personnel' tree can refer to the child of the 'employee' node by name as follows:
salary >= 50000 and location.state in ('NY', 'NJ')

When this condition is attached to the 'employee' node, the result of the query will only consist of the employees matching the criteria. The expression can refer to the immediate child of the selection node, or any descendent of the selection node. A child of the immediate child can be referenced by concatenating the name of the immediate child with the name of its child, separated by a dot. This notation can be used to reference child nodes multiple levels down the tree.
The selection node can exist anywhere in a tree path: At the beginning, in the middle, or as the last node. If multiple selection nodes are present in the tree path, a condition can be attached to each selection node. The query engine performs filtering starting at the top of the tree. If a selection node returns multiple nodes based on the condition, each node is processed further at the next tree path level. This process is done recursively until all branches are processed. The collection of all selected sub-trees becomes the child nodes of a new root node.
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