Context.Several empirical studies have explored the benefits of software design patterns, but their collective results are highly inconsistent. Resolving the inconsistencies requires investigating moderators—i.e., variables that cause an effect to differ across contexts.Objectives.Replicate a design patterns experiment at multiple sites and identify sufficient moderators to generalize the results across prior studies.Methods.We perform a close replication of an experiment investigating the impact (in terms of time and quality) of design patterns (Decorator and Abstract Factory) on software maintenance. The experiment was replicated once previously, with divergent results. We execute our replication at four universities—spanning two continents and three countries—using a new method for performing distributed replications based on closely coordinated, small-scale instances (“joint replication”). We perform two analyses: 1) apost-hocanalysis of moderators, based on frequentist and Bayesian statistics; 2) ana priorianalysis of the original hypotheses, based on frequentist statistics.Results.The main effect differs across the previous instances of the experiment and across the sites in our distributed replication. Our analysis of moderators (including developer experience and pattern knowledge) resolves the differences sufficiently to allow for cross-context (and cross-study) conclusions. The final conclusions represent 126 participants from five universities and 12 software companies, spanning two continents and at least four countries.Conclusions.The Decorator pattern is found to be preferable to a simpler solution during maintenance, as long as the developer has at least some prior knowledge of the pattern. For Abstract Factory, the simpler solution is found to be mostly equivalent to the pattern solution. Abstract Factory is shown to require a higher level of knowledge and/or experience than Decorator for the pattern to be beneficial.

Context: Conventional wisdom, inspired in part by Eric Raymond, suggests that open source developers should---and primarily do---develop software for developers like themselves. We refer to the production of software primarily for the benefit of developers as reflexivity, and we evaluate the applicability of this concept to open source software (OSS) by studying SourceForge projects. Objective: The goal of this research is to test Eric Raymond's assertions with respect to OSS success factors. Method: We present four criteria by which to assess project reflexivity in SourceForge. These criteria are based on three specific indicators: intended audiences, relevant topics, and supported operating systems. Results: We show in this short paper that 68% of SourceForge projects are likely reflexive (in the sense described by Raymond). Further, 76% of projects exceeding one million downloads are reflexive, 79% for projects exceeding ten million downloads, and 89% for projects exceeding one hundred million downloads. Conclusion: These results tentatively support Raymond's assertions that 1) OSS projects tend to be reflexive and 2) reflexive OSS projects tend to be more successful than irreflexive projects. Causality, however, is not addressed.

The RESER workshop provides a venue in which empirical software engineering researchers can discuss the theoretical foundations and methods of replication, as well as present the results of specific replicated studies.

Building non-trivial software is a social endeavor. Therefore, understanding the social network of developers is key to the study of software development organizations. We present a graph representation of the commit behavior of developers within the Apache Software Foundation for 2010 and 2011. Relationships between developers in the network represent collaborative commit behavior. Several similarity and summary metrics have been pre-calculated. The data, along with the tools that were used to create it and some further discussion, can be found at: http://sequoia.cs.byu.edu/lab/?page=artifacts/apacheGraphs.

Coordination of project stakeholders is critical to timely and consistent software delivery. In this short paper we present the problem of private information as a guiding framework or lens through which to interpret coordination dynamics within software organizations. We provide evidence of this problem in the form of specific challenges, collected via interviews from a diverse set of extended (i.e., non-development) stakeholders in a globally distributed software development organization.

The RESER 2010 workshop provides a venue in which empirical Software Engineering researchers may present and discuss theoretical foundations and methods of replication, as well as the results of replicated studies.

We present the results of a study in which author entropy was used to characterize author contributions per file. Our analysis reveals three patterns: banding in the data, uneven distribution of data across bands, and file size dependent distributions within bands. Our results suggest that when two authors contribute to a file, large files are more likely to have a dominant author than smaller files.

As wireless devices continue to become more prevalent, heterogeneous wireless networks - in which communicating devices have at their disposal multiple types of radios - will become the norm. Communication between nodes in these networks ought to be as simple as possible; they should be able to seamlessly switch between different radios and network stacks on the fly in order to better serve the user. To make this a possibility, we consider the challenging problems of when two communicating devices should decide to switch to a different radio, and which radio they should choose. We design an autonomous and intelligent radio switch (AIRS) decision algorithm that uses predicted radio availability and user profiles to choose the best available radio for two adjacent devices. The decision algorithm uses several parameters to avoid switching radios too frequently. We use a simulation study to evaluate the best settings for several parameters, then show that the AIRS system performs better than several alternative algorithms. AIRS is able to provide dynamic, but stable radio switching, while balancing the competing objectives of high throughput and low power consumption.

Communication between wireless devices ought to be as simple as possible; they should be able to seamlessly switch between different radios and network stacks on the fly in order to better serve the user. To make this a possibility, we consider the challenging problem of predicting link quality in a changing mobile environment. In this paper we present an algorithm that uses Weighted Least Squares Regression to predict whether a given link can meet application requirements in terms of throughput, delay, and jitter. We use a simulation study to demonstrate that our algorithm is able to predict link quality accurately and stably in a frequently changing mobile environment. The prediction algorithm is more accurate than several alternative algorithms, and the overhead caused by the link measurements is negligible in terms of throughput and power consumption.

Devices with multiple wireless interfaces are becoming increasingly popular. We envision that these devices will become the building block for future mesh networks, providing seamless connectivity across a range of heterogeneous devices. Although these devices typically implement frequency sharing, using either direct sequence spread spectrum (DSSS) or frequency hopping spread spectrum (FHSS), they may still interfere with one another. In this paper we provide a novel radio interference avoidance (RIA) algorithm that solves the problem of interference between IEEE 802.11 and Bluetooth. We then extend this algorithm to other types of DSSS and FHSS combinations. Though the algorithm is limited to devices with both of these interfaces, this is a very common case. We analytically derive the expected value of the response time for RIA and run simulations to demonstrate its effectiveness. Our results indicate that RIA is able to eliminate interference with a very short response time. RIA also outperforms adaptive frequency hopping, a solution proposed by the IEEE 802.15 co-existence working group.

Transport selection mechanisms are designed to facilitate seamless connectivity in heterogeneous multi-transport environments, allowing access to the "best" available transport according to user requirements. Evaluating transport configurations dynamically according to the user's preferences and quality of service (QoS) requirements is a challenging task. This paper describes a quantitative approach that applies the Utility Theorem and Nash's Bargaining solution to heterogeneous wireless environments. The mathematical model presented generates and adjusts the transport preference list dynamically depending on the degree to which a transport satisfies user preferences and the application's QoS requirements. We incorporate a negotiation engine using the axiomatic multi-transport bargaining algorithm to integrate local and remote users' requirements in a mutually beneficial manner as devices are connected via a peer-to-peer link. The transport selection model discussed in this paper is computationally light with modest communication overhead, making it suitable for mobile devices

This paper presents prioritized soft constraint satisfaction (PSCS), a novel approach to selecting the ''best" transport in dynamic wireless transport switching systems. PSCS maintains a satisfying connection to another end point by choosing transports based on a user-established range of preferences and priority for criteria such as speed, power, range and cost. Additionally, feedback is provided regarding tradeoffs among the criteria, thus enabling the user to adjust inputs according to the capabilities of the system. We also recommend guidelines for setting preferences and priorities.

In this paper, we introduce quality of transport (QoT), an architecture for synergistically and autonomously managing session-layer protocol access to multiple transports in heterogeneous wireless environments. We present an overview of the QoT architecture including: 1) transport discovery, 2) service discovery, 3) object exchange, 4) transport switching, and 5) intelligent transport selection. Preliminary successes with our design and implementation of QoT suggest that dynamic intelligent autonomous transport switching can help to optimize user experience and session layer performance in multi-transport environments.

This paper demonstrates that careful tuning of the OBEX and IrLAP negotiated parameters allows OBEX to scale well for use with large data objects and high transmission rates. Due to the substantial time overhead inherent in link turnarounds, minimizing turnarounds during the transmission of a large object helps to maximize link efficiency. The IrLAP window size and OBEX packet size significantly impact the number of required turnarounds during the transmission of a large object. When these parameters are properly tuned, maximum throughput can be achieved, and OBEX performs efficiently at high data rates.

In order to utilize multiple transports, devices must discover common mechanisms for communication, a procedure we call multi-transport discovery. The multi-transport discovery algorithm presented in this paper is a four-phase procedure (transport probing, transport querying, address-to-device mapping, and transport accessibility) that can discover common transports within a multi-transport environment. Transport probing uses a transport-dependent device discovery mechanism to discover an initial link. Transport querying communicates over the probed link to query additional transports. Address-to-device mapping correctly correlates each transport to a remote device. Finally, transport accessibility periodically ascertains link availability during an application session.

This paper describes a mechanism for utilizing inverse multiplexing to significantly increase the bandwidth available to short-range wireless devices. Previous work with inverse multiplexing has focused on wired networks; its implementation with short-range wireless transports introduces heterogeneity in the links, which must be taken into account. A mathematical model for an inverse multiplexing system is derived for several scheduling algorithms. Both process limited and transport limited systems are examined. The validity of this model is shown by our implementation of an inverse multiplexing layer that uses IrDa and Bluetooth transports. Concepts related to inverse multiplexing such as usage models, negotiation, quality of service, and the simultaneous use of multiple Bluetooth transports are discussed.

In resource-limited mobile computing devices, Bluetooth wireless technology imposes a weighty burden due to inefficient power utilization and a sluggish device discovery process. Buttressing Bluetooth with radiofrequency identification (RFID) technology by performing an operation we call "Rendez-Blue" alleviates these limitations. In the Rendez-Blue process, an RFID signal is used as a cue to "wake-up" a sleeping Bluetooth radio. This ensures that the Bluetooth radio is active only when needed, significantly reducing power consumption. In addition, RFID is used to communicate Bluetooth device information, allowing the user to bypass the traditional 10.24-second discovery process.

Bluetooth device discovery is a time-intensive phase of the Bluetooth connection-establishment procedure. In this paper we propose a technique that integrates existing IrDA technology with Bluetooth technology to improve the ad hoc connection establishment time of Bluetooth devices. We accomplish this improvement by first establishing an IrDA connection between two devices equipped with both Bluetooth and IrDA capabilities and then exchanging Bluetooth device discovery information via the established IrDA connection. As a result of this cooperative exchange, the devices are able to bypass the time-intensive Bluetooth device discovery procedure. Our research shows that IrDA-assisted Bluetooth connection establishment is up to four times faster than the normal ad hoc Bluetooth connection establishment procedure. In addition, it provides other time-savings in subsequent device selection procedures.

The Infrared Data Association's (IrDA) infrared data transmission protocol is a widely used mechanism for short-range wireless data communications. In order to provide flexibility for connections between devices of potentially disparate capabilities, IrDA devices negotiate the values of several transmission parameters based on the capabilities of the devices establishing the connection. This paper describes the design and implementation of a software tool, Irdaperf, to model IrDA performance based on negotiated transmission parameters. Using Irdaperf, we demonstrate that for fast data rates, maximizing the window size and data size are key factors for overcoming the negative effects of a relatively long link turnaround time. At slower speeds (especially 115.2 Mbps and below), these factors have a less pronounced effect.