In patent law, it is the "claims" that defines the metes and bounds of an invention. In other words, claims define the scope of patent right. Claims are drafted such that it defines the boundaries of the invention with a purpose of providing clear notice of the claimed invention.

Patentees usually try to increase the scope of the claim by defining the claims with functional limits rather than structural limits. The claims that define functional limits in a patent specification are usually known as functional claim. Functional claiming is a common drafting technique used to describe the features by what it does rather than by what it is. Functional claiming is desirable since it covers all the materials, or acts for accomplishing a function by a specific means.

Functional claims are usually used in various technologies; however, patent applications for computer related inventions tend to use functional claims more often. A patent application is allowed to claim an invention in functional terms in exchange for disclosing structures in the specification which clearly perform the claimed function.   

Even though using functional language limits the scope of a claim, there is a tendency for functional limitations to blur the boundaries of a claim’s scope. The instant issue is addressed by 35 U.S.C. § 112 (f) in the US. This section limits a functional claim (means-plus-function claim) element to the particular technologies described in the specification and the equivalents thereof.

35 U.S.C. § 112 (f):

Element in Claim for a Combination.— An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.

In a computer related invention, the patent application may disclose a computer processor or hardware that may be sufficient for enabling a general computing function. However, mentioning a computer processor or hardware may not be sufficient for enabling a structure for performing a specific function, since novelty in computer related inventions most often resides in the software or the computer program that is being executed on the computer processor or the hardware, not the hardware itself. Generally, in inventions related to technologies, such as mechanical engineering, the corresponding structure for functional claim is easily identifiable. However, when it comes to identifying the “corresponding structure” for a computer related invention (ex: means for selecting a data file), an “algorithm” is the one which carries out the claimed function, and is usually regarded as the corresponding structure for a computer-implemented means-plus-function limitation.

For example, if an encoder is claimed using functional language, disclosure of a computer processor or hardware may not be sufficient for enabling a structure for performing the claimed encoding function. The specification must describe in detail, may be by using a flow chart, the method of carrying out the function recited in the claims.

The U.S. Court of Appeals for the Federal Circuit has held means-plus-function claims invalid on several occasions for failure to disclose algorithm (not necessarily in the form of source code) used to perform the function.  

In Augme Technologies v. Yahoo, concerning indefiniteness of claims, the United States Court of Appeals for the Federal Circuit affirmed the district Court’s judgment. Claims 19 and 20 were held indefinite under 35 U.S.C. § 112.  The claims recited “means for assembling, at said server system, said second computer readable code module,”

The Court held:

"We affirm the district court’s conclusion of indefiniteness because the ’691 patent does not disclose any algorithm for assembling the second computer readable code module."

“It is undisputed that “means for assembling” is a computer-implemented means-plus-function limitation. Thus, to meet the definiteness requirements of 35 U.S.C. § 112, second paragraph, the specification must disclose an algorithm for performing the claimed function. Net MoneyIN, Inc. v. VeriSign, Inc., 545 F.3d 1359, 1367 (Fed. Cir. 2008). Certainly, the algorithm may be expressed in “any understandable terms including as a mathematical formula, in prose, or as a flow chart, or in any other manner that provides sufficient structure.”

In another case, Ergo Licensing, Inc. v. Carefusion, the court held:

“Because general purpose computers can be programmed to perform very different tasks in very different ways, simply disclosing a computer as the structure designated to perform a particular function does not limit the scope of the claim to ‘the corresponding structure, material, or acts’ that per-form the function, as required by section 112 paragraph 6.” Id. Requiring disclosure of an algorithm properly defines the scope of the claim and prevents pure functional claiming.

Conclusion

Adequate measure has to be taken to enable a means-plus-function limitation present in a claim on a computer related invention. The specification must disclose the algorithm that can be used to perform the function of the means-plus-function limitation. The algorithm need not necessarily be in the form of source code; the algorithm may be expressed in any understandable terms, such as mathematical formula, in prose, or as a flow chart, or in any other manner that provides sufficient structure.

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