ECLA Classification System

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NOTE: The ECLA classification was frozen as of July 2012, and is no longer being applied to new patent documents. The Cooperative Patent Classification has totally replaced the ECLA system. Searchers may still wish to use ECLA codes for historical reasons, but the EPO no longer hosts the ECLA class definition schedule.

ECLA stands for European Classification, and was designed in-house by the EPO as an enhancement to the IPC classification system. Major features/advantages of the system are:

  • Highly skilled personnel. ECLA classes are only assigned by the EPO examining corps, which means that a small body of highly trained individuals maintains the relevance of the system and ensures the accuracy of its use. In contrast, IPC classes are applied by examiners all over the world, many of whom have insufficient training. IPC class searching can result in poor search quality due to inconsistent indexing efforts. Because of this high standard of quality, users can feel more confident when searching with ECLA classes.
  • Narrow class definitions. As the body of patent literature expands, IPC subgroups naturally grow in size. Because a sub-categorization that still contains thousands of documents hinders the ultimate purpose of a classification scheme (to eliminate the need for keyword searching), ECLA classes are defined to split these large IPC subgroups into even smaller divisions. Whereas IPC has around 67,000 subdivisions as of late 2005, the ECLA classification had around 129,000.[1]
  • Accelerated revision schedules. ECLA was developed as a flexible classification system that would change and grow with fast-moving technologies. This feature was originally in contrast to the inflexible 5-year revision schedule of the IPC; however, since the institution of IPC reform in January of 2006, Advanced IPC codes now offer the same advantage as ECLA.
  • Backfile updates. ECLA classification codes were developed for electronic database indexing purposes, meaning that they were never printed on paper copies of patent documents. As ECLA classifications are revised, EPO examiners re-index their backfile of documents for major patenting authorities, to keep ECLA searching current and accurate. Originally, this feature was in contrast to IPC revisions, which were not retroactively applied to published documents. However, since IPC reforms were enacted in January 2006, electronic records for already-published documents will be continually updated as IPC class definitions change.
  • Non-patent literature indexing. EPO examiners use ECLA codes to classify non-patent literature documents they come across during examination. These documents are part of the EPO’s searchable files, and are currently loaded into some free (esp@cenet) and commercial (Questel-Orbit) search providers as well.

Disadvantages or other considerations to account for when searching using ECLA include:

  • ECLA classes are not published on the document when it is issued; they are assigned as in-computer codes by European patent examiners, and usually become available several months after publication. For this reason, ECLA classes should not be counted on to retrieve very recently issued documents. Search strategies must encompass other methods to ensure that newly published documents will be covered.

Because they function to further subdivide IPC classes, ECLA codes are presented in formats very similar to IPC classes, e.g. C02F9/00.

Optionally, an ECLA subgroup is added onto the end of the IPC subgroup to denote a further division in scope. These can be just letters, or a combination of letters and numbers, to denote further delineation within ECLA. For example:

C02F9/00 Multistage treatment of water, waste water, or sewage

This classification and definition is shared by ECLA and IPC-8 class definitions as of 7/2007.

ECLA-specific subclasses under C02F9/00 include:

C02F9/00H Applied to water conditioning, e.g. for industrial water supply, production of potable water, surface water treatment.
C02F9/00H2 Mobile treatment plants, e.g. mounted on a vehicle.
C02F9/00H4 Portable or detachable small-scale treatment devices (single-stage processes, optionally in combination with filtration techniques C02F1/00D or C02F1/00E4)

According to the EPO, even though IPC reforms will increase the similarities between the IPC and ECLA classification systems, ECLA will still continue to be revised and maintained as a supplemental, but independent, classification system for most technical fields.[2]

ECLA Y-Codes

Most recently, ECLA Y-codes have been created as an extension of the original classification system, to extend classification capabilities to new technology areas of special interest, and are usually added in addition to codes in the A through H series. The Y classification was created specifically to cover "General Tagging of New Technological Developments."

Subjects covered by ECLA Y codes originally included nanotechnology topics. In 2010, a new set of Y codes were added for clean energy technologies. [3]

ICO Codes

ECLA classes can be extended through a set of additional codes used by EPO examiners, referred to as ICO (or In-Computer-Only) codes.

According to Questel-Orbit’s user materials, ICO symbols are derived from classification symbols, with a different first letter: instead of A, B, C, D, E, F, G, and H, the letters K, L, M, N, P, R, S, and T are used. The ICO symbols may be either entirely or partially derived from the ECLA symbols; however, there are also symbols that are not derived from an existing symbol.[4]

ICO codes are used to describe the less important characteristics of the patent document, or to include a secondary classification (when one group takes precedence over another group). Finally, the codes may be used to classify additional subject matter or characteristics of the document when an EPO examiner feels that the material could be useful to another’s search.[4]

The characteristics of ICO codes as a secondary classification system may have inspired the IPC reform codes to include a “non-invention” code designation.


  1. European Classification (ECLA) information page, hosted by the esp@cenet website, online. Earliest publication date Dec 18, 2005. Verified by the wayback machine at Accessed July 16, 2007,
  2. "FAQ on IPC Reform." esp@cenet website, Accessed on July 17, 2007.
  3. van Dulken, Steve. "New patent classifications for clean energy." The Patent Search Blog, Posted June 22, 2010. Accessed June 22, 2010.
  4. 4.0 4.1 "Questel-Orbit data sheet for ECLA classification file." Accessed on January 30, 2008.

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