An ISA must endeavour to discover as much of the relevant prior art as its facilities permit, and must, in any case, have regard to what is known as 6.1.2.5 Minimum Documentation. The process of “having regard to” particular search material should have as its first phase an assessment by the three person team [including the search examiner] of the probability of finding highly relevant citations. Where the three person team concludes that this probability is low, it is open to the three person team to decide not to search that material.

The PCT International Search and Preliminary Examination Guidelines state:

“The international search is essentially a thorough, high quality, search of the most relevant resources, and the report serves to provide information on the relevant prior art to the applicant, to the public ... and to the designated Offices and the International Preliminary Examining Authorities." [PCT/GL/ISPE/12 at para 15.18]

"Nevertheless, it must be realized that, even though completeness should be the ultimate goal of the international search, this goal may not be necessarily obtained because of such factors as the inevitable imperfections of any classification system and its implementation, and may not be economically justified if the cost is to be kept within reasonable bounds. The examiner therefore considers the most relevant search resources for the technology, including databases listed in the Search Guidance Intellectual Property Digital Library (available through the WIPO web site at www.wipo.int), and organises the search effort and utilizes the search time in such a manner as to reduce to a minimum the possibility of failing to discover existing highly relevant prior art, such as complete anticipations for any claims. For less relevant prior art a lower retrieval ratio can be accepted.” [PCT/GL/ISPE/12 at para 15.20]

“Often various search strategies are possible that are relevant to the subject matter of the application. The examiner should exercise judgement based on experience and knowledge of the search resources, to select the search strategies most appropriate to the case in hand, and establish the order in which various strategies (i.e., classification places, databases, and other resources) are to be consulted accordingly. This process should give precedence to the main technical field of the invention, and to the search resources and strategies in which the probability of finding relevant documents is highest.” [PCT/GL/ISPE/12 at para 15.47]

For an example examiner’s should consider the independent claim(s) and the inventive concept first when determining a search strategy. The search strategy should also cover significant features defined in dependent claims or features that the application might be reasonably expected to be directed towards after amendment, taking into account the inventive concept of the application read as a whole, and the relevant common general knowledge in the art. This could result in searching other classification areas or using alternative keywords.

If a significant feature is not forthcoming from the search, examiners should use their judgement as a person skilled in the art to determine if continuing the search is warranted. If it is, specific targeted keywords related to the missing feature should be used.

Some examples of when additional searching is not necessary are set out in Paragraph A13.13 of the PCT ISPE Guidelines. Namely where:

a technical feature known in a technical field is applied from its original field to another field and its application therein would have been obvious to a person skilled in the art;
a difference between the document’s content and the claimed matter is so well known that documentary evidence is unnecessary;
the claimed subject matter relates to the use of a known product, and the use would have been obvious from the known properties of the product;
the claimed invention differs from the known art merely in the use of equivalents that are so well known that the citation of documentary evidence is unnecessary.

No special search should be made for features that are so well known that documentary evidence seems to be unnecessary, however, if a handbook or other document showing that feature is generally known can be found rapidly, it should be cited. See Paragraph 15.28 of the PCT IPSE Guidelines.

Paragraph 15.31 of the PCT ISPE Guidelines states:

“For claims characterized by a combination of elements (for example, A, B and C), the international search should be directed towards the combination; however, when searching classification units (see chapter 7) for this purpose, sub-combinations, including the elements individually (for example, AB, AC, BC and also A, B and C separately), should be searched in those units at the same time. A search in additional classification units either for subcombinations or for individual elements of the combination should only be performed if this is still necessary for establishing the novelty of the element in order to assess the inventive step of the combination.”

The PCT International Search and Preliminary Examination Guidelines at paragraph 15.52 state as follows:

"The examiner carries out the international search, directing attention to any prior art likely to have bearing on novelty or inventive step. In addition, the examiner is encouraged to cite any prior art likely to be of assistance in determining sufficiency of description through the whole of the field claimed, see paragraphs 5.52 and 5.53 and the requirement that the claimed invention be fully supported by the description, see paragraphs 5.54 to 5.58. The examiner should also note any documents that may be of importance for other reasons, such as documents putting doubt upon the validity of any priority claimed, contributing to a better or more correct understanding of the claimed invention, or illustrating the technological background; but the examiner should not spend time in searching for these documents, nor in the consideration of such matters unless there is a special reason for doing so in a particular case. Documents which do not qualify as prior art because they post date the claimed invention may nevertheless be cited to show a universal fact, such as characteristics or properties of a material, or a specific scientific fact, or to show the level of ordinary skill in the art."

The examiner may truncate a search, where appropriate:

“Reasons of economy dictate that the examiner use appropriate judgement to end the search when the probability of discovering further relevant prior art becomes very low in relation to the effort needed. The international search may also be stopped when documents have been found clearly demonstrating lack of novelty in the entire subject matter to which the claims are directed, apart from features the application of which would not involve an inventive step and which are instantly and unquestionably demonstrable as being well known in the field under consideration such that documentary evidence seems to be unnecessary.” [PCT/GL/ISPE/12 at para 15.61].