Abstract:
A software development environment for developing application software for a target computing platform, having target platform licensed software components subject to target platform license terms, the development environment isolates source platform application source code for the application software from being subjected to the target platform software license terms while allowing the application source code to indirectly refer to the target platform licensed software components having the target platform license terms. A license isolation layer may include an interface definition and an implementation of the interface definition. The application source code binds to the implementation of the license isolation layer interface definition. The software development environment includes a compiler that compiles the application source code such that it is isolated from applicability of the target platform license.

Description:
[0001]    This application is a Divisional of co-pending application Ser. No. 10/265,819, filed on Oct. 7, 2002, the entire contents of which are hereby incorporated by reference and for which priority is claimed under 35 U.S.C. § 120. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to software licenses and more particularly to isolating source code from a target platform software license that is incompatible with the source code&#39;s license. 
       BACKGROUND OF THE INVENTION 
       [0003]    Developing software for a computing platform is greatly simplified when the software being developed can use services provided by the computing platform. As used in this document, the term platform includes, but is not limited to, a software operating system and/or open computer-system hardware, which a third party could write software for. Software licensing issues may arise however, if the target platform and the software being developed have incompatible software licenses. 
         [0004]    There are several types of software licenses, involving both source code and object code. Some examples of commonly used source code licenses include Berkeley Software Design (BSD), GNU Public License (GPL), and Sun Community Software (SCSL). In addition, various companies make their source or object code available under a wide variety of licenses. Some source licenses are commonly referred to as “open” source licenses since they typically allow further modification and use of the source with a variety of restrictions and constraints. Some open source licenses, such as the GPL, impose constraints on the restrictions that can be placed upon GPL licensed code. The GPL is intended to guarantee developers&#39; freedom to share and change GPL licensed software by, among other things, requiring software developers to disclose their source code for GPL-licensed software. According to the GPL license, any code released under the GPL must remain under the GPL. This has the effect of requiring any modifications to code released under the GPL and any code “mixed” with the GPL to all be released under the GPL. To legally include GPL code in a program, developers must release their program—and disclose their source code—under the GPL. 
         [0005]    However, there may be times when a developer desires to combine their code with code released under an open source license without subjecting their code to the same license. Various licenses take various approaches to this situation. For example, the BSD license typically allows such a situation (e.g. it does not require that code combined with BSD licensed code must be released under any specific type of license). The GPL, on the other hand, takes the opposite approach and, at least on its face, purports to preclude such a scenario. As an alternative to the GPL, the Free Software Foundation issued the GNU Lesser General Public License (LGPL), which contains provisions that attempt to specify whether software that uses or is combined with LGPL-licensed software is subject to the LGPL. However, for a variety of reasons, it can be difficult to determine when code that uses or is combined with LGFL-licensed code must be released under the LGPL. What is needed is a mechanism that can be used to develop code that can clearly be released free of any license restrictions of related code. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention addresses situations where it can be difficult to determine which license terms might apply to developed software code that is to be combined with other software code released under licenses that purport to restrict the terms under which other software can be released. The invention uses a “license isolation layer” of software which insolates one group of code from the license terms of another group of code. The invention also describes a software development method and related technology and methods to achieve “license isolation” between two groups of code. This summary should not be used to interpret the specific scope of the invention, which is set by the claims appended herewith, nor to identify significant elements which must accompany any embodiment of the invention. This summary is provided for the sole purpose of setting out a simple summary of one possible embodiment of the invention. The full scope and description of the invention should be taken from the appended claims and detailed description. 
         [0007]    A license isolation layer isolates one group of code (application code) from underlying code licensed according to terms that purport to restrict how application code must be licensed. A license isolation layer developed according to the present invention is developed according to specific guidelines, set based on the terms of the license of the underlying code. The license isolation layer typically includes a license isolation layer interface definition that is outside of the scope of the underlying code license. The license isolation layer may also include an implementation of the license isolation layer interface definition that makes use of the underlying code. The application source code may use the license isolation layer interface definition and bind to the implementation of the license isolation layer interface definition without binding to target platform licensed software components. In this way, the license isolation layer can prevent the application source code from being subject to the target platform software license. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  depicts a prior art scenario for porting an application program to run on a target platform. 
           [0009]      FIG. 2  shows a scenario similar to  FIG. 1  that includes an inventive license isolation layer interface definition and an implementation of the interface definition. 
           [0010]      FIG. 3  is similar to  FIG. 2  with the license isolation layer header acting as a buffer between the application source code and the license isolation layer library, which may be subject to the target platform license. 
           [0011]      FIG. 4  shows steps of a method, in accordance with an embodiment of the invention, for isolating application source code from an incompatible target platform software license. 
           [0012]      FIGS. 5A and 5B  show steps of a method, in accordance with an embodiment of the invention, that is similar to, and more detailed than, the method shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Before describing embodiments of the invention in more detail, a few terms will be defined. Application Programming Interface (API) refers to an interface between two software modules, programs, objects, etc. that enables one software module to access functionality provided by the other software module. A specific example of an API is the interfaces that an application program may use to access a computer&#39;s operating system to request it carry out services on its behalf. Other examples abound. Source code refers to a set of instructions, written in a programming language that is translated to object code through compilation or some other process before the program can be run on a computer. Object code, as used herein, can refer both to binary object code, sometimes referred to as native code or executable, and intermediate language code. The term “code” without further delineation is used to refer to both object code and source code. 
         [0014]    Library refers to a file that stores related modules of object code. A library may implement in object form an API set interface definition from a corresponding header file. Stated differently, a header file may describe a set of system services provided by a library that implements, in object form, the set a system services described by the header file. 
         [0015]    Platform is a loosely defined term for a software operating system and/or hardware, for which a third party can write software. Target platform refers to a platform for which application software is being developed and/or upon which the application software will run. Source platform refers to a platform used for developing application source code. Note that a platform can be hardware, software, or a combination of both. Also note that the source platform and target platform may reside physically on the same machine (or separate machines), even though they are separate platforms for the purposes of this invention. 
         [0016]    Linking refers to combining several programs or modules, some of which are intended to be used together—but which were written separately—into a single program, which may be executable even though the separate programs were not themselves directly executable. 
         [0017]      FIG. 1  depicts a prior art scenario for developing an application program to run on, and use services provided by, a target platform. Compilation of application source code  102  along with an interface definition  108  produces an application object file  112  that may be subject to the license of the interface definition  108 . This type of license is also referred to in this document as a target platform license. Application object file  112  being subject to the license of the interface definition  108  could in turn result in application source code  102  having to be provided under the terms of the target platform license. 
         [0018]    The interface definition  108  and the implementation of the interface definition  110  together depict the general scenario for various programming languages in which the interface definition  108  essentially provides a language system that tells application developers, and a compiler, how to use services provided by the implementation  110  of the interface definition  108 . Interface definition  108  could be a C/C—header file, metadata for XML, class information for Java, and the like. 
         [0019]    The arrow from interface definition  108  to application source code  102  indicates that application source code  102  makes use of the interface definition  108 . In the context of the C programming language, this could be done using an include statement. The arrow from application source code  102  to the implementation  110  of the interface definition  108  indicates that the application source code  102  binds to the implementation  110 . 
         [0020]      FIG. 1  depicts a source platform licensed environment  100  separated by dashed line  114  from a target platform licensed environment  106 . Note that the developer may desire to release application source  102  or application object file  112  under different terms than the license for target platform  106 . However, given the prior art method of developing application object file  112 , that may not be possible. Dashed line  116  depicts that the compiler  104  may not be licensed under the source platform license or the target platform license. In subsequent figures, this detail related to licensing of the compiler is omitted to improve the clarity of the drawings. 
         [0021]      FIG. 2  depicts a example scenario for developing application source code  206  for a target platform according to the present invention.  FIG. 2  includes the source platform licensed environment  100 , compiler  104 , target platform licensed interface definition  108 , target platform licensed implementation  110  of interface definition  108 , target platform licensed environment  106 , and dashed line  114  as described above in connection with  FIG. 1 . 
         [0022]      FIG. 2  also depicts a license isolation layer interface definition  200 , an implementation  202  of license isolation layer interface definition  200 , and application source code  206  in accordance with an embodiment of the invention. The license isolation layer interface definition  200  is created according to rules based on an interpretation of the target platform license in order to create an isolation layer between application source  206  and the underlying target platform implementation  110 . For example, isolation layer  202  may be created in accordance with a strictest reasonable interpretation of the target platform license so that the license isolation layer interface definition  200  falls outside the scope of the target platform license. 
         [0023]    The application object file  204  may use the implementation  202  of the license isolation layer interface definition  200  for various services. The implementation  202  of the license isolation layer interface definition  200  may use the target platform licensed interface definition  108  and may use the target platform licensed implementation  110  of the interface definition  108  for various services. 
         [0024]    In this way, the application source code  206  may be prevented from binding directly to the target platform licensed implementation  110  of the target platform licensed interface definition  108 . The application source code  206  may bind instead to the implementation  202  of the license isolation layer interface definition  200 . As described in more detail below, the license isolation layer interface definition  200  or both the license isolation layer interface definition  200  and its implementation  202  may prevent the target platform license from becoming applicable to the application source code  206 . 
         [0025]    The implementation  202  may be built in accordance with a strictest reasonable interpretation of the target platform license so that the license isolation layer interface definition  200  may fall outside of the Scope of the target platform license. In this way, both the application source code  206  and the source code (not shown) for the implementation  202  of the license isolation layer interface definition  200  can be isolated from the target platform license. 
         [0026]    Even if the implementation  202  of the license isolation layer interface definition  200  falls within the scope of the target platform license, the application object file  204  and the application source code  206  can still be isolated from the target platform license as long as the license isolation layer interface definition  200  falls outside the scope of the target platform license. 
         [0027]      FIG. 3  shows another embodiment of the invention that is similar to the embodiment shown in  FIG. 2 . The license isolation layer interface definition  200  and the implementation  202  of the license isolation layer interface definition  200  are respectively replaced in  FIG. 3  by a license isolation layer header  300  and a license isolation layer library  304 , which is depicted in the target platform licensed environment  106 . 
         [0028]    Like the license isolation layer interface definition  200 , the license isolation layer header  300  may be created in accordance with a strictest reasonable interpretation of the target platform license. Similarly, license isolation layer library  304  may be built in accordance with a strictest reasonable interpretation of the target platform license, as was discussed above in connection with the implementation  202  of the license isolation layer interface definition  200 . 
         [0029]    Although license isolation layer library  304  is shown within the target platform licensed environment  106  in  FIG. 3 , the license isolation layer library  304  could be isolated from the target platform license if the license isolation layer library  304  is built in accordance with a strictest reasonable interpretation of the target platform license. Regardless of whether the target platform license applies to the license isolation layer library  304 , if the license isolation layer header  300  is created in accordance with a strictest reasonable interpretation of the target platform license, the license isolation layer header  300  may still prevent the target platform license from becoming applicable to the application object file  204  and the application source code  102 . 
         [0030]    The application object file  204  may use the license isolation layer library  304  for various services. The license isolation layer library  304  may use the target platform licensed header  302  and may use the target platform licensed library  306  for services. In this way, the application source code  206  may be prevented from binding directly to the target platform licensed library  306 . The application source code  206  may bind instead to the license isolation layer library  304 . The license isolation layer header  300  or both the license isolation layer header  300  and the license isolation layer library  304  may prevent the target platform license from becoming applicable to the application source code  206 . 
         [0031]    Isolation or adaptation layers have been used in a variety of circumstances in software engineering. In all cases, technical concerns have driven such isolation layers. For example, an adaptation layer may be created to translate calls of one form into calls accepted by an underlying platform in order to allow two otherwise incompatible programs, objects, systems, etc. to intemperate. However, the isolation layers of the present invention (such as implementation  202  and isolation library  304 ) are created not based on technical concerns, but based on rules and interpretations of the licenses that apply to the underlying target platform. 
         [0032]    To further illustrate some principles of the present invention, an example will be presented using the LGPL as the underlying target platform license. This license example is selected simply because the LGPL terms are well known and it provides an adequate illustration of various principles of the invention. The principles of the invention can be applied to many other licenses and the inclusion of the example should not be used in any way to limit the scope of the invention. 
         [0033]    In order to present the example, it is necessary to discuss certain key terms of the LGPL. The first four paragraphs of section 5 of the LGPL (Version 2.1), which are reproduced below, permit linking LGPL libraries into non-LGPL-licensed software without subjecting the non-LGPL-licensed software to the LGPL:
       5. A program that contains no derivative of any portion of the Library, but is designed to work with the Library by being compiled or linked with it, is called a “work that uses the Library”. Such a work, in isolation, is not a derivative work of the Library, and therefore falls outside the scope of this License.   However, linking a “work that uses the Library” with the Library creates an executable that is a derivative of the Library (because it contains portions of the Library), rather than a “work that uses the library”. The executable is therefore covered by this License. Section 6 states terms for distribution of such executables.   When a “work that uses the Library” uses material from a header file that is part of the Library, the object code for the work may be a derivative work of the Library even though the source code is not. Whether this is true is especially significant if the work can be linked without the Library, or if the work is itself a library. The threshold for this to be true is not precisely defined by law.   If such an object file uses only numerical parameters, data structure layouts and accessors, and small macros and small inline functions (ten lines or less in length), then the use of the object file is unrestricted, regardless of whether it is legally a derivative work. (Executables containing this object code plus portions of the Library will still fall under Section 6.)       
 
         [0038]    These provisions of the LGPL provide an example of a difficult line-drawing problem that certain licenses create. The LGPL provisions above try to distinguish between: (1) a work that uses the library and that is therefore not subject to the LGPL; and (2) a derivative work of the library that is subject to the LGPL. The fourth paragraph of section 5 of the LGPL essentially says that if an object files uses less than a threshold amount of implementation from an LGPL-licensed library, then the LGPL will not apply to the object file. The rationale for subjecting object files, and source code, to the LGPL when they use more than the threshold amount of an LGPL-licensed library is as follows. If an object file uses more than the threshold amount of implementation, then if the library is modified, the library vendor may need to modify the source code for the object file to get the source code and the modified library to work together properly. 
         [0039]    Whether the LGPL will apply to application source code is significant in the context of development of closed source software for a platform in which system services, such as application programming interfaces (APIs) for accessing files and memory and the like, are contained in LGPL-licensed software. If, under the terms of the LGPL, the closed source application software is a work that uses the library, then the application source code does not have to be distributed. If the closed source application software is a derivative work of the LGPL-licensed software, however, then the closed source application software would have to be distributed under the terms of the LGPL. 
         [0040]    Thus, it is necessary to create a set of rules from the LGPL license that can be used to create the isolation layer of the present invention. According to the description above, one approach is to identify the strictest reasonable interpretation of the license to allow for uncertainty in the terms of the license, such as are illustrated by the LGPL license above. In the case of the LGPL, the terms of the license specify that object files using “only numerical parameters, data structure layouts and accessors, and small macros and small inline functions (ten lines or less in length)” will be free from the license restrictions of the LGPL. Thus, a license isolation layer developed according to these guidelines should be free from the license terms of the LGPL. 
         [0041]    Development of an isolation layer according to guidelines derived from the terms of the target platform license may require isolation between development groups, restricted information flow, or the like. 
         [0042]      FIG. 4  depicts steps of a method in accordance with an embodiment of the invention. Dashed line  412  separates the source platform licensed environment  100  from a license isolation layer implementation environment  400 , which could be consistent with either the application source code license or the target platform license. Step  402 . is directed to creating a license isolation layer interface definition that is outside the scope of the target platform license and to which a source platform license optionally applies. Such an interface definition may then be passed from the source platform licensed environment  100  to the license isolation layer implementation environment  400 , as shown at  404 . 
         [0043]    Step  406  is directed to building an implementation of the license isolation layer interface definition that is optionally subject to the source platform software license. Such an implementation may then be passed from the license isolation layer implementation environment  400  to the source platform licensed environment  100 , as shown at  408 . The implementation of the license isolation layer interface definition may make use of a target platform licensed interface definition and a target platform licensed implementation of the target platform licensed interface definition. 
         [0044]    Step  410  is directed to building a target application using the license isolation layer interface definition and the implementation of the license isolation layer interface definition. In this way, the target application can be isolated from the target platform software license. 
         [0045]      FIGS. 5A and 5B  depict steps of a method in accordance with another embodiment of the invention. The steps shown in  FIGS. 5A and 5B  are similar to, and more detailed, than the steps shown in  FIG. 4 .  FIGS. 5A and 5B  can represent an example embodiment of the invention where the LGPL applies to the underlying target platform environment. 
         [0046]    In  FIG. 5A , Step  500  is directed to creating a license isolation layer header file that contains type and structure definitions and function prototypes for implementing a license isolation layer API set. Such a header file may exclude in-line functions and macros longer than one line. The license isolation layer header file is passed, optionally in read-only format, from the source platform licensed environment  100  to the license isolation layer implementation environment  400 , as shown at  502 . 
         [0047]    Step  504  is directed to building a license isolation layer library that implements the license isolation layer API set in an environment that optionally contains no target application source code and that optionally does not contain header files that are not licensed under the LGPL. In building the license isolation layer library, in-line functions and macros longer than one line may be avoided. 
         [0048]    If any changes to the license isolation layer header file are desired, the changes may be made by returning to step  500  as indicated by the yes branch from decision step  506 . Otherwise, the steps continue in  FIG. 5B . 
         [0049]    The license isolation layer library API set implementation is passed, optionally without the license isolation layer library source code, from the license isolation layer implementation environment  400  to the source platform licensed environment  100 , as shown at  508 . Step  510  is directed to using the license isolation layer header file and the license isolation layer library to build the target application to bind to the license isolation layer library. During this step, source code, headers, and code libraries from sources other than the license isolation layer header file and the target application may be excluded from the source platform licensed environment. 
         [0050]    While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and methods that fall within the spirit and scope of the invention as set forth in the appended claims.