Appendix A - Structure of the Modern Schedule

Over the years, the USPTO has used many schemes to provide a framework that is uniform for the entire classification system as well as to provide schemes that optimize a class's usefulness as a search aid.

The current philosophy on the organization of patent data was formulated in early 1964 and was set forth in the publication Development and Use of the Patent Classification Systems (DUPACS) which was issued in January 1966 and is now out of print. The publication United States Patent Classification Standards and Practices (USPCLASP) has replaced DUPACS. 

USPCLASP sets forth a model (shown below) that should be used in the creation of a new classification system; i.e., a class. However, this model is a theoretical standard and many deviations will be found in practice. The primary reason for these deviations is that all classes are built based upon a thorough review of the art to be contained in the new class. The structure of the class is dictated by the art itself. This review of the actual documents frequently causes modification of the theoretical model.

The specific arrangement of subclasses within a schedule will define that schedule's hierarchy as noted in the main portion of this handbook. The hierarchy will almost invariably arrange the subject matter with the most complicated and comprehensive material at the top of the schedule and the simpler material at a lower position in the schedule.

Further, all modern schedules exhibit exhaustive subclasses. This concept is discussed in depth in the main body of this handbook.

With these preliminary thoughts and reservations, a discussion about the preferred theoretical structure of the "Modern" class will now take place.

The "modern" class is often represented as an inverted right triangle.


Image of an inverted right triangle. The "modern" class is often represented as an inverted right triangle.


As you can see in the above scheme, the subject matter is arranged from the most complicated (the top of the triangle) to the simplest (the bottom of the triangle). A, AB, Ap, and X are the four characters of subject matter in the above scheme. "A" represents the basic subject matter of the class, e.g., in a class of pumps.

  • "A" would be the types of pumps found in the class (e.g., jet pumps, reciprocating pumps, etc.);
  • "AB" represents the basic subject matter combined with subject matter having a different proximate function, effect, or product; that is, the subject matter of another class (e.g., a pump combined with and driven by a vehicle);
  • "Ap" represents the basic subject matter combined with a perfecting feature, i.e., some structure that enhances or improves the operation of basic subject matter device (e.g., an intercooler located between stages of a pump which improves the overall efficiency of the pump by carrying away unwanted heat generated during the pump's operation);
  • "X" represents the subcombinations of the basic subject matter or elements peculiar to or associated with the basic subject matter, when such subcombinations or elements are not specifically provided for in some other class (e.g., pump casings, etc.).

In addition to subclasses providing for the above noted material, modern schedules frequently provide for the following additional concepts:

a. Condition Response (Automatic Control)
b. Measuring and Testing
c. Special "A"
d. Convertible
e. Combined
f. Plural "A"
g. Miscellaneous

A brief description of each of the above types of subclasses is given below.

Condition Response (Automatic Control)

Condition response is a broad concept that embraces the variant, Automatic Control, within its boundaries. Condition responsive subclasses are intended to provide a home for devices that include a means to sense a randomly occurring condition or change in condition that will effect a change in the operation of a device provided for in the class. This concept embraces devices as complicated as a milling machine with means to sense the position of a cutting head and acts to disable the machine if any misalignment is sensed. It also includes within its scope a device as simple as a pressure biased check valve, wherein the under surface of the valve seat senses fluid pressure which causes the valve to unseat when the pressure against the underside of the seat reaches a predetermined point.

"Automatic Control" is a more restrictive concept that includes means to sense a randomly occurring condition or change of conditions that operates on a separate means to effect control of an apparatus, e.g., the milling machine mentioned above. This concept requires a sensor, e.g., a slipper or feeler located adjacent to the system, which senses a condition or change in condition, e.g., tool misalignment. Once this condition is sensed, the sensing means operates on another device, e.g., a switch or valve, which controls a different medium to regulate the operation of the controlled device. There has been a tendency in recent years to move away from the title "Automatic Control" and to substitute the title similar to "Control Means Responsive to Sensed Condition."

Another concept closely allied to Automatic Control is Programmed or Cyclic Control. These devices frequently include sensors; however, the device employing the sensors merely performs repetitive operations. There is a basic "law of the machine" and the sensors are actuated in sequence to control the operation of the device based on that law. In other words, the condition sensed is predictable rather than random.

Also embraced by this concept are those devices that employ stored intelligence (e.g., magnetic tape) to control the operation of the machine in a prescribed, repetitive fashion.

These subclasses are generally grouped in the same area of the schedule and this area is generally located relatively high in the schedule.

Measuring and Testing

Many classes provide for their basic subject matter combined with some type of measuring or testing device. This represents a special type of "AB" combined subclass, but is no different in character than any other "AB" type subclass. In fact, its only distinction is its frequent occurrence.

Combined subclasses drawn to a class's basic subject matter combined with heating or cooling means or lubricating means are also frequently found in many modern classes.

Special "A"

It frequently happens that special collections of unique basic subject matter are provided for very high in the class schedule. These collections are of special search value and could get lost if they were positioned lower in the schedule. This collection will also appear above the "Combined" subclass even though they are not very complicated and are not drawn to combinations or basic subject matter plus perfecting feature. An example of one such collection is drawn to getter type pumps in Class 417.


This subclass provides for devices which, while they are the basic subject matter of one class, are intended to be changed into the basic subject matter of another class by a rearrangement of their parts. This concept also provides for the change of one type of device provided for in a given class into a different type of device also provided for in the same class by rearrangement of the parts of the device.


As previously noted in this handbook, "Combined" represents a dividing point in the schedule. Unless a note to the contrary appears, the subclass is exhaustive of all combinations, i.e., "AB" type and "Ap" type subclasses not provided for higher in the schedule.

Generally, all subclasses appearing below "Combined" will be drawn to either the basic subject matter of the class or to the subcombination and elements peculiar to or associated with that subject matter.

Therefore, a "Combined" subclass, in practice, is a "Miscellaneous" subclass for combinations not provided for elsewhere.

Plural "A"

Another type of collection that frequently appears in a modern schedule is one drawn to systems employing multiple devices provided for in the class. The multiple devices may be of the same type or they may be different types, e.g., two diaphragm pumps connected in series or a diaphragm pump and a reciprocating piston type arranged in the same fashion.

This subclass is usually positioned immediately below the "Combined" subclass.


In many modern schedules, the last subclass contained in the schedule is "Miscellaneous."

This subclass is defined in extremely broad terms and is intended to be exhaustive of all subject matter admitted to the class but not provided for higher in the class. Each "Main Line" subclass is exhaustive for the material provided for in that main line; however, there will often be a residue of material that does not fit the existing "Main Lines." If a "Combined" subclass exists in the schedule, only unprovided for basic subject matter and unprovided for subcombinations and elements will be found in "Miscellaneous." It must be remembered that "Combined" is exhaustive of combinations of the basic subject matter and the subject matter of some other class.

In conclusion, the above model is a theoretical model, and many deviations will be found in practice, e.g., Classes 198 and 251 contain no "Combined" subclass even though they are modern classes. This omission was a conscious act of the Classifier involved and was dictated by the nature of the art embraced by the class.

One must always carefully review a schedule while using it to look for exceptions from this model.

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