A Novel Mathematical Formula for Retrieval Algorithm

Table 1

Data structure of a binary tree.

Field	Data type	Meaning
Formula element	String	Operator, variable, or constant
Category	String	OPS (satisfying the commutative law), VAR (variable), OPU (not satisfying the commutative law), and CON (constant)
Priority	Integer	Operator priority (the larger the value is, the higher the priority is; maximum machine number if priority is for variables and constants)
Combination	String	LR (left-right), UD (up-down), and SG (single)
Node height	Integer	The height of the binary tree that regards current node as root
Structure code	String	Structure code of current node = structure code of its left child + node height + its structure code of right child