Feature Comment: The Heightened Disclosure Requirement for Software Claimed Using Means-Plus-Function Limitations

By Gregory L. Clinton[1]


The question of whether a computer component discloses adequate structure for a corresponding means-plus-function claim limitation has been a recurrent issue in recent Federal Circuit jurisprudence, most recently in the cases of Blackboard Inc. v. Desire2Learn Inc., 91 U.S.P.Q.2d 1481, 1483 (Fed. Cir. 2008).  and Net MoneyIN Inc. v. VeriSign Inc., 88 U.S.P.Q.2d 1751 (Fed. Cir. 2008).    In both cases the specification of the patents at issue did not provide adequate support for means-plus-function limitations in the claims.  Although the use of means-plus-function claims has fallen out of favor in recent years, means-plus-function claims remain useful in some situations.  Accordingly, a brief discussion on what to include in a specification to ensure proper support for such claims may be helpful to avoid problems during prosecution or litigation


Both of the two cases previously mentioned, Blackboard and Net MoneyIN, revolved in part around whether the specification provided adequate support for particular mean-plus-function limitations.  In both cases, the specification was found not to provide adequate support because the specifications merely described a general purpose computer, without any corresponding “structure” to which the means-plus-function claims could be tied.  In Blackboard, the patent was directed toward an Internet-based educational support system.  Blackboard Inc. v. Desire2Learn Inc., 91 U.S.P.Q.2d 1481, 1483 (Fed. Cir. 2008).  The claim limitation at issue recited “means for assigning a level of access to and control of each data file based on a user of the system’s predetermined role in a course…”  Id. at 1490.  Blackboard argued that the corresponding structure was an “access control manager” disclosed in the specification, citing to a particular paragraph describing the access control manager in largely functional terms.  Id.

The district court disagreed, finding the specification lacking the necessary structure to support the “means for assigning”, and the Federal Circuit affirmed.  Blackboard at 1490.  The Federal Circuit found that the access control manager was nothing more than a “black box”.  Id.  The specification provided no insight as to how the access control manager carried out the disclosed functionality.  Id.  In particular, the specification did not describe the structure of the access control manager or explain the process by which the access control manager performed the disclosed function.  Id.

The Federal Circuit rejected Blackboard’s arguments that the disclosed access control manager could be any computer device or program that performs the function of access control.  Blackboard at 1491.  The Federal Circuit viewed the argument as an attempt to avoid the requirement to disclose the structure associated with the means-plus-function limitation.  Blackboard was attempting to avoid the “price” of the means-plus-function limitation (namely, the requirement to disclose the corresponding structure) by attempting to claim the structure in purely functional terms, without any limit imposed by a structure disclosed in the specification.  Id.  What is important, the Federal Circuit held, was the means for achieving the intended outcome, not a mere description of that outcome.  Id.

One of the cases cited in the Blackboard decision, Net MoneyIn, Inc.  v. Verisign, Inc., expanded on the requirements in the disclosure for means-plus-function claims and computer-related structures.  The limitation in that case was a “means for generating an authenticating indicia” as part of a recited “first bank computer”.  Net MoneyIn, Inc. v. Verisign, Inc., 88 U.S.P.Q.2d 1751, 1755 (Fed. Cir. 2008).  After concluding that the limitation was properly construed as a means-plus-function limitation, the Federal Circuit looked to the specification for the corresponding structure, and found only a description of a general purpose bank computer that could be programmed to perform the recited function.  Id

The Federal Circuit reviewed prior holdings that the structure disclosed in the specification must be more than simply a general purpose computer.  Net MoneyIN at 1755.  If the disclosed structure is a computer, then the disclosure must be directed not to the general purpose computer itself, but to the algorithm which the general purpose computer is programmed to perform.  Id.  The operation of the algorithm performed by the general purpose computer transforms the general purpose computer into a special purpose computer designed to perform the disclosed algorithm.  Id.  Thus, if the specification fails to disclose the algorithm performed by the general purpose computer to carry out the recited function, then the claim is invalid under 35 U.S.C. § 112 for failing to disclose the necessary structure corresponding to the means-plus-function limitation.  Id. at 1757.


The Federal Circuit’s decision in the Blackboard and Net MoneyIn cases relied on its prior decision in WMS Game Inc. v. Int’l Game Tech., which in turn drew upon the landmark State Street Bank and Alappat decisions.  The patent at issue in WMS Gaming was directed toward an improved slot machine.  WMS Gaming, Inc. v. Int’l Game Tech., 51 U.S.P.Q.2d 1385, 1387 (Fed. Cir. 1999).  In traditional mechanical slot machines, reducing the probability of winning required either increasing the number of reels in the machine or increasing the number positions in each reel, neither of which appealed to players.  Id. The patent at issue in the case disclosed an electronically controlled slot machine.  Id.  The reels in the machine served only to display the results selected by the electronic control system.  Id.  The control system randomly selects a number from a range greater than the number of positions on the reel, looks up the corresponding result in a mapping table, and controls the reels to display the selected result.  Id.

The claim term at issue recited “a means for assigning a plurality of numbers representing said angular positions of said reel, said plurality of numbers exceeding said predetermined number of radial positions such that some rotational positions are expressed by a plurality of numbers.”  The district court interpreted the term to refer to “any table, formula, or algorithm for determining correspondence between the randomly selected numbers and rotational positions of the reel.”  WMS Gaming at 1391.  The Federal Circuit, however, found this interpretation to be too broad.

The flaw in the district court’s construction, the Federal Circuit held, lay in the district court’s failure to limit the claim to the algorithm disclosed in the specification.  WMS Gaming at 13.  The Federal Circuit reasserted its opinion in Alappat that a general purpose computer programmed to perform a given algorithm in effect becomes a new computer.  The general purpose computer in effect becomes a special purpose computer performing the disclosed algorithm.  Id. (citing In re Alappat, 31 U.S.P.Q.2d 1545, 1558 (Fed. Cir. 1994)).  Thus, in the context of means-plus-function claims, the structure is not the general-purpose computer, but rather the special purpose computer programmed to carry out the disclosed algorithm.  Applying this construction to the “means for assigning” limitation, the Federal Circuit held the corresponding structure to be a processor programmed to carry out the algorithm disclosed in Figure 6 of the patent.

The algorithm was disclosed in the patent at issue in WMS Gaming in the form of a diagram illustrating the operation of the algorithm.  However, patent applicants can express the algorithm in a variety of ways.  The algorithm can be explained as a diagram (as in WMS Gaming), as a mathematical formula, as a flowchart, or in prose. See Finisar Corp. v. DirecTV Group, Inc., 86 U.S.P.Q.2d 1609, 1623.


The Federal Circuit’s justification for defining algorithms as the important element for computer-related structures corresponding to a means-plus-function limitation relies upon the concept that a general purpose computer performing a disclosed algorithm can be seen as a special-purpose computer programmed to perform the function.  From this premise, it follows that a special-purpose computer could also be used as a sufficient structure.  Instead of disclosing an algorithm and a general-purpose computer to perform the algorithm, a patent applicant can instead disclose a special-purpose computer as the corresponding structure for a means-plus-function limitation.  Such a disclosure could come in the form of, for example, a detailed circuit diagram or schematic of the individual components of the special purpose computer.  A patent applicant may find such an alternative useful in situations where the novelty or inventive aspect lies more in the structure of the component than in the algorithm to be performed.


Federal Circuit jurisprudence permits the algorithm to be disclosed in a variety of ways.  The algorithm may be disclosed by a flowchart, a diagram, a formula, or prose.  Finisar at 1623.  Several cases illustrate the variety of ways in which a patent can disclose the necessary algorithm to support a means-plus-function case.  For example, the algorithm in WMS Gaming was disclosed by a combination of prose description in the specification and a figure.  See U.S. Patent No. 4,448,419 at Fig. 6 and col. 4, line 55 – col. 5, line 5.

In Harris Corp. v. Ericsson Inc., the algorithm was disclosed in a flowchart and corresponding textual description.  Harris Corp. v. Ericsson Inc., 75 U.S.P.Q.2d 1705, 1714 (Fed. Cir. 2005) (citing to various portions of U.S. Patent No. 4,365,338, including a flowchart shown in Figs. 8A and 8B).  The Federal Circuit disagreed with the district court’s finding that the recited “time domain processing means” corresponded to the disclosed “symbol processor”, because the symbol processor did not incorporate a disclosed algorithm.  The Federal Circuit instead found the disclosed structure to correspond not only to the symbol processor (which in turn included a support processor and a fast array processor) but also to a data recovery algorithm performed by the support processor.  Id.  The data recovery algorithm was disclosed in the specification as a flowchart diagram and corresponding description.  SeeU.S. Patent No. 4,365,338 at Figs. 8A, 8B, and 9.

The knowledge of a person of ordinary skill in the art can also support a disclosed structure or algorithm.  The patent at issue in AllVoice Computer PLC v. Nuance Communications Inc. recited an “output means” as a part of a system to facilitate speech recognition.  AllVoice Computer PLC v. Nuance Communications Inc., 84 U.S.P.Q.2d 1886, 1891.  AllVoice’s patent was directed toward an interface that converted spoken words into a data format compatible for word processors.  Id. The specification disclosed a speech recognition interface which, as part of its functionality, received a translated word and output the word via a dynamic data exchange (DDE) protocol.  Id.  Expert testimony established that this protocol was well known to persons of skill in the art of Windows programming.  Id. Thus, the person of ordinary skill in the art would have been well apprised of a structure corresponding to the disclosed DDE protocol. 

The AllVoice decision contrasts with the Blackboard and Net MoneyIn cases discussed above.  In both cases, the patentee attempted to rely upon the knowledge of a person of ordinary skill in the art to support the disclosed structure, but of the three, only AllVoice succeeded in convincing the Federal Circuit.  The distinguishing feature lies in the  extent to which the parties relied upon the knowledge of the person of ordinary skill in the art.  The disclosures of the Net MoneyIN patent and the Blackboard patent contained no element or internal structure of the various components.  The components were simply “black boxes” that a person of ordinary skill in the art could have programmed to perform the recited function.  Compare Net MoneyIN, 88 U.S.P.Q. 2d at 1756 and Blackboard, 91 U.S.P.Q.2d at 1491.  However, the disclosure of the AllVoice patent described the structure of the component in terms that would be understood by a person of ordinary skill – namely, the DDE component, which was a structure known in the art for carrying out a particular function.  This provided enough structure to render the corresponding means limitation definite.


As can be seen in the above cases, patent application drafters should pay special attention to the specification if means-plus-function claims are to be used.  If computer components are to be disclosed as the structure corresponding to a means-plus-function, either the specific structure of the corresponding component(s) should be disclosed (i.e. a special-purpose computer), or the algorithm carried out by the corresponding component(s) should be disclosed.  The algorithm can be disclosed in a variety of ways, including flowcharts, written explanation, diagrams, mathematical formulae, or a combination of these.  By disclosing the algorithm and the particular components, the careful patent drafter can avoid the definiteness problems that arose in Net MoneyIN and Blackboard.

[1] Gregory L. Clinton is an associate at Stein McEwen, LLP.  The opinions in this article do not represent the official positions of Stein McEwen, LLP.


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