Patent claims rely solely on text. However, it is difficult to define the scope of a patent right by describing an inventive concept or feature by text alone. It is not uncommon for a patent claim to involve function as well as structure, ingredients and movement. Appropriate interpretation of the scope of features defined by functional description has been a matter of longstanding controversy.
The existing Patent Examination Guidelines (issued in 2013) do not deny the legitimacy of such claims employing functional description. The guidelines stress only that a claim employing a solely functional description without any other technical feature will fail to meet the requirements for clarity and definiteness. The guidelines provide two kinds of functional feature:
- object defined by function; and
- means plus function.
'Object defined by function' is exemplified by claim language, such as 'storage device' and 'output circuit' (IP Court Judgment 103-Civil-Patent-Suit 48), which has been commonly used or recognised by persons in the art for a long time and is easily understood. Interpretation of the claim language 'object defined by function' should include all objects and means which can perform such function.
'Means plus function' must meet the following requirements:
- the claim language is in the form of 'means for...'; and
- the claim language does not cover all necessary structures, materials and movements for performing the claimed function.
In addition, interpretation of means-plus-function language must include the structures, materials and movements for performing the function, as well as its limitations and the equivalent scope thereof. However, if a functional description in a claim is not apparently drafted in the form of 'object defined by function' or 'means plus function', how should it be interpreted?
The Amended Points of Patent Infringement Assessment, which are undergoing public discussion before final drafting by the patent office, provide a third type of functional feature known as the functional clause. For example, in the claim description 'a changing direction device... comprising... whereby... to quickly change the operation direction', the language 'whereby... to quickly change the operation direction' is a functional clause, not object defined by function or means plus function. However, is a functional clause to be considered a limitation of the claim scope? The assessment provides the following opinions:
- If the functional clause describes only the result that the technical feature is intended to achieve, it should not be considered a limitation of the claim scope; and
- Since the functional clause is part of the claimed features, it apparently relates to the limitations of the claim scope.
IP Court Judgment 99-Civil-Patent-Suit-58 adopted the second opinion because it indicates that:
"a functional clause relates to the limitations of claim scope; according to the All-Elements Rule, it has to be taken into consideration when the claim is compared with prior art and the accused product."
Though the Amended Points of Patent Infringement Assessment provide a definition of 'functional clause', it remains unclear whether a claimed feature drafted as a functional clause would be considered means-plus-function language if it does not contain all necessary structures, materials and movements for performing the claimed function. Interpretation of functional features and descriptions will merit the scrutiny of future court and patent office practice.