The International Patent Classification (IPC) is a system for archiving and retrieval of patents based on technical content.  All published patent documents are classified according to the IPC, with codes for each technical field relevant to the invention(s) therein.  The classification system is hierarchically based.  The IPC is split into two levels, Core and Advanced.

Users not familiar with the IPC are strongly advised to read The WIPO Guide for IPC.  Copies of the Guide can also be viewed at both our Kilkenny and Dublin offices.

Core Level

The Core level (CL) contains about 23,000 classification places, and forms the basis of the IPC.  Classification places are relatively broad in scope.  This level of the IPC is used by the smaller Patent Offices, whose collection of patent documents is relatively small.  All Irish national published applications and granted patents (IEs) are classified according to the IPC’s Core level.  It is revised every three years to cater for emerging technologies, and to coordinate with changes in the Advanced level.


Advanced Level


The Advanced level (AL) contains over 70,000 classification places.  It is hierarchically based on the Core level of the IPC, but technical fields are more greatly subdivided.  All granted European Patents designating Ireland (EPs) are classified (by the European Patent Office (EPO)) using the Advanced level.  The Advanced level is revised every three months, allowing large Patent Offices to give the most accurate classifications possible to new patent documents.


Relationship between Core and Advanced levels


Every AL classification place has a formal CL equivalent.  Hence, EPs carry classification according to both levels of the IPC, the CL classification being generated automatically from the AL.  A quick overview of the relationship between the CL and AL IPC can be seen in this excerpt. 


A62C 8/00

Hand tools or accessories specially adapted for fire-fighting, e.g. tool boxes

A62C 8/02

. Buckets or pails

A62C 8/04

. Rakes or beaters

A62C 8/06

. Fire-blankets

A62C 8/08

. Shields


A62C 8/00 is an IPC CL place for technical matter related to fire-fighting accessories.  IPC AL also contains this place, but with 4 subdivisions. So a fire-fighting hand-shield or shield accessory would be AL classified in A62C 8/08, whereas the equivalent CL classification is A62C 8/00.  Indeed, in the AL, only fire-fighting hand tool or accessories not relating to buckets, pails, rakes, beaters, fire-blankets or shields would go in A62C 8/00, whereas all relevant technologies go to A62C 8/00 in the CL, which is the formal CL equivalent for any of AL A62C 8/00–08.


In theory, an AL classification should give rise to a specific CL classification.  In practice, however, a small number of discrepancies between the two levels exist, partly because of the difference in the revision cycles for the two levels, and partly due to the operation of precedence notes and references in the AL which are not visible to CL users.  Hence, mismatches do occur between the intellectually applied CL classification for a patent and the automated CL code generated from an applied AL classification.


Using the IPC to search the patent database.


The IPC search query module consists of two entry fields, one each for CL  and AL codes.  Associated with each entry field are two tick boxes, for designating IE or EP in respect of a given code.



Since there are two types of patent valid in Ireland, each classified according to different levels of the IPC, this search engine allows the user to search the two parts of the national collection separately or in combination.  The user can also choose for either patent type independently which level of the IPC to use.  The following table summarises the results to be expected for each selection.


Since both types of patent carry CL classifications, both sets can be searched directly using the IPC CL.  Please note, however, that whereas a CL search of IEs will return hits from Irish patents with CL classifications as applied by the Irish Patent Office, the same search for EPs will return EPs whose automated CL classification set contains the code specified.


An EP AL search will return patents with the specified code as applied by the EPO.  Though IE patents do not formally carry Advanced level classifications, a search of IEs will return any patent with the formal CL equivalent.  This will of course create a certain amount of “noise”, since the equivalent CL place to a given AL place is generally somewhat broader in scope.  However, the volume of Irish national documents is considerably less than for EP designates, so this is not such a problem.


Users may also combine CL and AL searches.  For instance, specifying a code in each entry field, the user may select IE at Core level and EP at Advanced level.  This strategy ensures that the user is searching according to classification codes applied by examiners according to strict IPC usage, and avoids the problem of discrepancies between intellectual and automated CL assignations.