It is the purpose of this chapter to provide a plan for classification of positions whereby—

(1) in determining the rate of basic pay which an employee will receive—

(A) the principle of equal pay for substantially equal work will be followed; and

(B) variations in rates of basic pay paid to different employees will be in proportion to substantial differences in the difficulty, responsibility, and qualification requirements of the work performed and to the contributions of employees to efficiency and economy in the service; and

(2) individual positions will, in accordance with their duties, responsibilities, and qualification requirements, be so grouped and identified by classes and grades, as defined by section 5102 of this title, and the various classes will be so described in published standards, as provided by section 5105 of this title, that the resulting position-classification system can be used in all phases of personnel administration.