First of all, what is a patent family? Like a family made up of people, it's a collection of things that are related in some way, where the things just happen to be patent documents. Although all methods of constructing a patent family are artificial, some are more artificial than others, which, I guess, implies that some are almost natural.
There are really two main types of patent family: simple and extended. These two are the most logical, but there are a few that aren't so logical, and really just exist so as to give a convenient name to a particular collection of patent documents.
The table below can be found in quite a few publications explaining how patent families are constructed. I'll add a bit of colour to it as we go to help explain the difference between the various types.
In a simple patent family all of the patent documents have exactly the same priority document (or documents), which means they all include basically the same inventive subject matter.
Essentially we're looking at a nuclear family. Mum and/or Dad are the priority documents, and their offspring are the patent documents.
Family 1 is a single parent family with one kid, while Family 2 is a two parent family with two kids, and so on. Things are kept, well, simple and easy to understand.
While each patent document belongs to a single family, this table clearly shows that a priority document can belong to more than one family, so where I say above that a patent family covers an inventive subject matter, it's not necessarily mutually exclusive with the subject matter of a second patent family. For example, Family 4 has the elements of Priority P3, which must also form part of Family 3's subject matter, but Family 3 also contains the elements of Priority P2, which is sufficient to differentiate it from Family 4 and to call it a separate patent family.
So, why don't we define a patent family by a single priority document instead...
A complex patent family is generally defined as one where all patent documents are linked by at least one priority document.
The definition says 'at least one' but the table below doesn't provide an example. In the table above, Family 2 could also be considered to be a complex patent family as it has a pair of priority documents that are both shared by Patent documents 2 and 3. It doesn't include Patent documents 1 and 4 as they don't share both priority documents.
Otherwise, this is a people family where the parents have separated. You have Family 1 with Mum with three kids, and Family 2 with Dad, also with three kids, but where two of the kids are in common. Depending on which family you are looking at, sometimes the kids in common are staying with Mum, and sometimes with Dad, and Dad's just hanging out for that one weekend in a blue moon when he has no kids at home and he can go and play a round of golf.
I prefer the simple patent family approach to this one as, in complex families, a single patent document can belong to more than one family. The simple family allows for the concept of patent equivalents. As the priority document and subject matter are the same, you can say that Patent document 2 is an equivalent of Patent document 3. You can look at the claims of one and be certain that they will be substantially the same as the other. It's handy when one of the patent documents is not in English as you can read an equivalent that is. You can't say the same about Patent documents 1 and 2 in complex Family 1.
So, what's the solution...
In an extended patent family all patent documents have at least one priority document in common with at least one other family member. An extended patent family is the marriage between a simple patent family and a complex patent family.
This can lead, in some instances, to extraordinarily large patent families where the family members are in a similar technical area, but with potentially a larger diversity because two family members with different priorities may cover different inventions.
Now you have Mum, your stepdad, Dad, Dad's new girlfriend, half brothers and sisters, cousins, second cousins once removed, aunts, and mad Uncle Bob, all of whom may live in different cities or countries, perhaps never having had met except for that one time when your grandmother died, and you wouldn't know them if you passed them in the street.
An extended patent family does provide the whole picture by putting everything you need to know in one place. From there you can tease out a number of simple patent families (or complex ones if that's your thing), or report the family as a whole. It really depends on the question you are looking to answer.
This is perhaps the most artificial of all the patent families. It draws together patent documents that are not related by a common priority, but is determined intellectually, i.e. by sitting down and using your necktop computer. Patent documents in technical families will sometimes have priority documents in common, but others will have same inventor(s), and the same or similar title, subject matter and drawings, and so should be included for a sense of completeness.
Patent documents can become separated from what would have been their simple patent family as a result of missing a convention filing or divisional applications not being connected properly with their parent application.
This has to be Kevin from Home Alone. Mom and Dad (Inventors 1 & 2) have applied for "Christmas Vacation" in the United States but have forgotten one of their patent documents when it came to flying out to the "Paris Convention".
A national patent family consists of any patent applications from a single country having at least one priority in common, so for example, in addition to the original application, patents of addition, divisional children, and continuations.
A domestic patent family relates to subsequent publications of same application, i.e. with same number but with different kind codes. For example the published application (A1) and the granted patent (B1).
Where can you find patent family data?
In an automated world, patent family information has to be constructed from priority data, which is why the technical family above has to be constructed manually. It also goes some way to explaining why some members can get separated from their patent family as priority data isn't particularly standardised. Even if you apply a reasonable standard, a missing or extra zero somewhere can throw the system out, but that's up to people like me to notice and correct.
The best free aggregating sources are the European Patent Office's INPADOC database available via Espacenet, and to a large degree, WIPO's PatentScope. Google Patents should also provide a reasonable patent family.
There are other free patent information databases, like Depatis and the USPTO, among many others, that you can use to construct your own patent family if you are so inclined, but that level of enthusiasm is best reserved for looking for any outliers in countries not usually covered by the aggregating sources.
The other sources are commercial patent databases such as PatBase or Derwent Innovation, among a few others, but of course you will need to pay for the privilege. Commercial patent database providers define patent families for their own purposes, whether it's to differentiate themselves from their competitors, or it's just easier to do from a technical viewpoint, but they are always mixtures of the types described above, and sometimes you have the option of choosing your family, unlike the real world.
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.
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