How are patents organized?

There are many patent offices around the world, and their patent classification systems are not the same. Luckily, most of the systems are based on very similar principles. And, knowledge of the United States Patent Office (USPTO) system and the European system is all that is required for the vast majority of patent searches.

The USPTO patent classification system
    Understanding the "Dot" System
    Subclasses are Not Cumulative
    Class and Subclass Definitions
Foreign Patent Classification Systems
Help with Patent Classification
Understanding Patent Numbers

1. The USPTO patent classification system

 
a. Understanding the "Dot" System
The United States Patent & Trademark Office (USPTO) classifies patents by subject matter. There are hundreds of different categories, and each of the categories has many sub-categories (and often, each of the sub-categories has sub-categories). A partial listing of one class might look like this:
Class 330 AMPLIFIERS
1R - WITH DIVERSE-TYPE ART DEVICE
1A - With process control system
2 - WITH AMPLIFIER CONDITION INDICATING OR TESTING MEANS
3 - WITH PLURAL DIVERSE-TYPE AMPLIFYING DEVICES
4 - WITH MASER-TYPE AMPLIFYING DEVICE
4.5 - PARAMETRIC AMPLIFIERS
4.6 - .Traveling wave type
4.7 - ..Electron beam device
4.8 - .Gyromagnetic type (e.g., ferrite)
4.9 - .Semiconductor type (e.g., with semiconductor diode)
5 - WITH SOLID ELEMENT WAVE PROPAGATING AMPLIFYING DEVICE

In this example, the class is 330. 330 is all about "Amplifiers". Each entry under 330 is a sub-category listing specific features of amplifiers. The location of a patent is written as its class, followed by a slash, and then its subclass, like so: 330/4.

What would you expect to find in a patent that was classified as 330/4? You would expect to find an amplifier (because everything under class 330 must be an amplifier), using a maser-type amplifying device (since that is the definition of subclass 4). It makes no difference if you know what a maser-type amplifying device is; this is just an example.

Now, what if you had an amplifier with a maser-type amplifying device that also had a process control system (the definition listed for subclass 1A)? How would you know where to look for related inventions? Would you look in 330/4, or would you look in 330/1A?

The answer is "both". There is no way of knowing under which class/subclass the USPTO examiners decided to file an invention. And, a single invention can be filed under more than one class/subclass (in fact, most inventions are filed in several classes/subclasses).

This is one of the most important challenges of patent searching: Thoroughly understanding the classification system, and wisely choosing which classes/subclasses appear to be most relevant to the search you are performing. If you choose poorly, there may be another class/subclass filled with dozens of patents relevant to your search, and you may miss them.

Don't worry too much though - there are ways of making sure that you are looking in the correct classes/subclasses, and we will explain how to do this in a bit.

You may have noticed the dots in front of the definitions for subclasses 1A, and 4.6 - 4.9. What are they? The dots indicate additional hierarchy levels in the class/subclass structure. In this example, the class (330) is at the highest level; everything else falls under class 330. But only some of the subclasses are directly under class 330. For instance, subclass 1R is directly under class 330. So are subclasses 2, 3, 4, 4.5, and 5. You know this because they have no dots in front of their definitions which would indicate additional steps down in the hierarchy structure. Subclass 1A on the other hand, is not directly under class 330. Rather, subclass 1A actually falls under subclass 1R. So, you could think of subclass 1A as being sub-subclass 1A.

Now look at subclass 4.7. It has two dots in front of its definition. That means it is still further down the classification tree. 4.7 is under 4.6, which is under 4.5, which is under class 330. So 4.7 is actually a sub-sub-subclass. But, all those "subs" would get to be confusing, so they just call them subclasses and distinguish the different levels with dots - the more dots, the lower it is in the hierarchy. If you are trying to figure out what class or subclass a given category falls under, go up the listing from the category of interest to the first class or subclass with one less dot.

It works just like an outline, but dots are used in place of Roman numerals, and other traditional outline level designations.

It is extremely important to understand this hierarchical system. If you do not understand the classification system, it is absolutely impossible to know if you are looking in right places when you do a search.

Here is an actual screen-shot of another partial class listing, with annotations:

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b. Subclasses are Not Cumulative
Be aware that upper level subclasses do not contain all the patents of the subclasses below them. In the example above, subclass 2 is indented under subclass 1. This does not mean that, if you did a search of subclass 1, you would find all the patents in subclass 2, plus some additional ones that were specific to subclass 1. It does not work that way. You must search the subclass at the lowest relevant level of the hierarchy. Patents are only filed in the upper levels of the hierarchy when there is no appropriate lower level in which to file them. To illustrate this concept, here is a very simple imaginary example:

Class 999 Cars
1 - .with blue paint
2 - ..with metallic paint
3 - .with red paint
4 - .with black paint

Where would you look for a car with blue metallic paint? Only 999/2. Because there is a specific subclass for blue metallic paint, all patents should be filed in that subclass. Filing mistakes aside, if you look in 999/1, you will find nothing - that is not the proper place, even though it is also for blue paint.

Where would you look for a car with green paint? In the main class, 999. This is because there is no subclass with an appropriate definition, leaving the examiner with no option other than to file the patent in the top level. So, only patents that do not have a more concise subclass available are filed in a given place. Or, to say this another way, patents are filed in the most detailed subclass available - so that is where you must look for them. Higher level classes and subclasses are only for patents which cannot be filed in a lower level subclass.

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c. Class and Subclass Definitions
A class and subclass searching and definitions are coming soon!

One tidbit of information to keep in mind for US classes/subclasses is that letters after a subclass (such as the "1A" and "1R" in the Amplifier example above) are special designations used for USPTO internal purposes. Because they are not official classes, they are ignored for definition purposes. In other words, 330/1R is often treated as if it were just 330/1. This distinction is of little importance, but it can be confusing if you do not know that sometimes the end letter is simply ignored.

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2. Foreign Patent Classification Systems

There are two other classification systems in common use in Europe. These systems are called the "IPC" (International Patent Classification) and the "ECLA" (European Classification).

The format of these classifications is as follows. A sample IPC would be C12N 7/00; it consists of a section (letter-C), class (numbers-12), subclass (letter-N), main group (numbers-7), a slash, and the subgroup (numbers-00). However, it may be as short as a section and class.

ECLA is really an extended version of the IPC system. ECLA adds addition letters or numbers on to the end of the IPC classification on to the end to allow for more categories, and thus hopefully more accurate categorization.

While the categories themselves are different from those found at the USPTO, the concept of searching the IPC or ECLA classifications is the same. Note that many US patents will have their foreign classifications listed on them as well, and this can be a helpful guide when trying to determine what foreign classes to search.

A guide to the IPC can be found at http://www.wipo.int/classifications/fulltext/new_ipc/index.htm and the IPC can be searched via keyword here: http://www.wipo.int/search/en/. Note that ECLA codes cannot currently be searched by keyword. However, the ECLA codes are so similar to the IPC codes that this is largely unnecessary.

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3. Help with Patent Classification

One method of making sure that you know which classes are relevant to a particular invention is simple (at least when it comes to US Patents): Ask! USPTO examiners are very willing to help you. The USPTO examiners are experts at classifying the inventions in their particular area, so it is good to get their opinion on where to search even if you think you have already located the best classes.

USPTO examiners have a duty of confidentiality. So, you can tell them whatever you want about the invention and they are not allowed to tell anyone else. Also, this is part of their job, so don't feel like you are imposing (but be VERY POLITE!). Many search firms contact examiners as a matter of course to get their opinions on what classes should be searched -- so the examiners expect it.

How do you go about doing this? First, you need to figure out what you think the most relevant class/subclass is. A good way to know this is to look at the classifications of the patents that you found in a keyword search, if you did the keyword search first. Or, take a few minutes to find some patents related to something similar to the disclosure invention, and see where they are classified. Once you have that information, there is a web page where you can look up what "Art Unit" handles a given Class or Subclass. An "Art Unit" is just a group of examiners that work on related subject matter.

So, let's say that you determine that the most relevant class/subclass for your search is 359/009 (Lasers and Holograms). You would go to this web page:
http://pair.uspto.gov/final/images/ArtSearch.html
and enter "359" in the class blank. Press the button, and you get a table that lists all of the Art Units that work on class 359. Scan down the subclass column, and you will see that Art Unit 2872 handles subclass 9. With that information in hand, you then visit this web page:
http://pair.uspto.gov/cgi-bin/final/employee_loc.pl?action=querypg

In the "Search by Organization" blank, enter 2872. That gives you a list, with phone numbers, of all the examiners that work in Art Unit 2872. So, you just pick one, give them a call, and say "Hi, I'm working on a novelty search about an invention which has these features... I think that I should be searching Class 359 Subclass 9, but I just wanted to make sure. What do you think?"

Sometimes they will say "Yes, you are correct". Sometimes they will give you some additional places to search. And sometimes they will say "I think you have the wrong Class/Subclass. You might want to try 283/86 (Printed matter with holograms), but my Art Unit doesn't work on that Class/Subclass, so try giving them a call".

This is really a detailed explanation for a simple step - just bookmark those web pages and it should only take 10 minutes or so.

Note that occasionally the USPTO's database is unavailable and the Art Unit search will not work. If that happens, you may find appropriate phone numbers on this page as well:
http://www.uspto.gov/web/info/pat-tech.htm

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4. Understanding Patent Numbers

When searching patents, you will encounter a variety of different patent numbering formats. For instance, you may see the same U.S. patent referred to as "6,000,000" or "US06000000" or even "US6000000B1."

Each of these designations means the same thing, but different databases present the numbers differently. The "B1" on the end of the last example simply stands for "granted patent", which brings us to the topic of Kind Codes.

There are many different designations, called Kind Codes, which can be appended to patent numbers and patent application numbers. Each Kind Code has a specific meaning, and while often not relevant for the purposes of patent searching, you should understand that Kind Codes exist so that you are not confused by them. Following is a table listing all current U.S. Kind Codes. Some of the table comments address the fact that the use of Kind Codes has not been consistent throughout history, so older patents may use different designations than current patents.

Note that foreign Kind Codes look similar, but they do not always have the same meanings. So, DO NOT assume that "A1" in the US means the same thing as "A1" elsewhere.
 

In addition, you will come across US patents with completely different numbering formats, including things such as D123456 (the "D" indicates that it is a design patent), PP01234 ("PP" indicates a plant patent), and RE12345 ("RE" stands for reissue).

It behooves you to have a basic understanding of these different numbering schemes. As patent searches rarely involve design patents or plant patents, reissues will be the most relevant to your searching (though even they will be rare). A reissue occurs when something in a previously-granted patent is found to be in error, and the patent must therefore be amended.

Finally, a document that you will rarely encounter, but should know that it exists, is the Statutory Invention Registration (SIR). The SIR is a document that allows an inventor to put an invention into the public domain. The SIR is not a patent, and does not afford any patent rights to the inventor. What it does do, however, is prevent anyone else from patenting the invention. SIR's replaced a previous type of document called a "Defensive Publication". Defensive publications no longer exist, but may be recognized by their unique numbering scheme, which starts with a "T", as in T998008.

Patent numbers are assigned sequentially by issue date (but SIRs are numbered sequentially by application date).

Following is a table the lists the first number for each type of patent issued in a given year. This information can help you perform "common sense" checks on your search results. For instance, if you are doing a Validity search, and your references must pre-date another patent with a priority date of Jan 1, 1990, and you see that you have included a reference to US patent, you know something might be amiss, because that patent was issued (not applied for) in 2001. Technically, you could be correct. The Priority Date on the patent could be before 1990 in certain circumstances, but it is unlikely.
 

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