Abstract-Software developers often need to port applications written for a source platform to a target platform. In doing so, a key task is to replace an application's use of methods from the source platform API with corresponding methods from the target platform API. However, this task is challenging because developers must manually identify mappings between methods in the source and target APIs, e.g., using API documentation.We develop a novel approach to the problem of inferring mappings between the APIs of a source and target platform. Our approach is tailored to the case where the source and target platform each have independently-developed applications that implement similar functionality. We observe that in building these applications, developers exercised knowledge of the corresponding APIs. We develop a technique to systematically harvest this knowledge and infer likely mappings between the APIs of the source and target platform. The output of our approach is a ranked list of target API methods or method sequences that likely map to each source API method or method sequence. We have implemented this approach in a prototype tool called Rosetta, and have applied it to infer likely mappings between the Java2 Platform Mobile Edition and Android graphics APIs. I. ISoftware developers often wish to make their applications available on a wide variety of computing platforms. The developer of a gaming app, for instance, may wish to make his app available on smart phones and tablets manufactured by various vendors, on desktops, and via the cloud. The key hurdle that he faces in doing so is to port his app to these software and hardware platforms.Why is porting software a difficult problem? Consider an example: suppose that we wish to port a Java2 Platform Mobile Edition (JavaME)-based game to an Android-powered device. Among other tasks, we must modify the game to use Android's API [10] (the target platform) instead of JavaME's API [21] (the source platform). Unfortunately, the process of identifying the API methods in the target platform that implement the same functionality corresponding to that of a source platform API method is cumbersome. We must manually examine the SDKs of the source and target APIs to determine the right method (or sequence of methods) to use. To add complexity, there could be multiple ways in which a source API method can be implemented using the target's API methods. For example, the fillRect() method in JavaME's graphics API, which fills a specified rectangle with color, can be implemented using either one of these two sequences of methods in Android's graphics API: setStyle();drawRect() or as moveTo();lineTo(); lineTo();lineTo();lineTo();drawPath() (we have omitted class names and the parameters to these method calls).One way to address this problem is to populate a database of mappings between the APIs of the source and target platforms. In this database, each source API method (or method sequence) is mapped to a target API method (or method sequence) that implements its f...

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