Playing Detective: Reconstructing Software Architecture from Available Evidence

Because a system's software architecture strongly influences its quality attributes such as modifiability, performance, and security, it is important to analyze and reason about that architecture. However, architectural documentation frequently does not exist, and when it does, it is often out of sync with the implemented system. In addition, it is rare that software development begins with a clean slate; systems are almost always constrained by existing legacy code. As a consequence, we need to be able to extract information from existing system implementations and utilize this information for architectural reasoning. This paper presents Dali, an open, lightweight workbench that aids an analyst in extracting, manipulating, and interpreting architectural information. By assisting in the reconstruction of architectures from extracted information, Dali helps an analyst redocument architectures, discover the relationship between as-implemented and as-designed architectures, analyze architectural quality attributes and plan for architectural change.     

A Wireless Instructor System for Computer-Supported Collaborative Learning Requiring Immersive Presence (CSCLIP)

The Computer-Supported Collaborative Learning Requiring Immersive Presence (CSCLIP) concept has been established with the objective of extending and enhancing thee-learning experience of distance education, especially for classes that involve laboratory (lab) experiments. The CSCLIP concept defines immersive presence as an inherent requirement that enables cognitive, affective, and most importantly psychomotor learning objectives to integrate into designs and concepts for next generation e-learning systems (Sharda et~al., 2003). Within the CSCLIP architectural framework, the Wireless Instructor (WI) system has been conceptualized and developed as an essential device to effectively support teaching while roaming instructional features for both local and distance students. The WI system provides cost effective means to establish a real-time immersive presence for the distance learning (DL) student and his/her lab group peers. The technical design and system architecture to create a WI system are introduced in this paper. The objective of the WI system is to make the learning experience more vivid and interactive by enabling the DL students, as well as the local students that are not in the same room with the instructor(s) at the same time, to be able to flexibly interact with the instructor(s) in real-time. With this system the students can experience real-time or non-real-time virtual tours with the instructor(s), enabling the students to visit places that may not be easily accessible due to distance, limited space and/or time, cost, or possible danger. The WI system consists of two major sub-components. First is a wireless audio and video (AV) system, which transfers real-time AV signals to and from the instructor(s) to all students. Second is the wireless instructor locator & data assistant system. These two systems can be combined into one WI unit, but as the applied development technologies are somewhat distinct, their features and architectural designs will be described separately throughout this paper. Integration of the two systems will enable further capabilities.This revised version was published online in March 2005 with corrections to the cover dateThis project was funded by the U.S. Department of Education (DoE) award no. P116Z020042 project titled Telecommunications Virtual Laboratory Development.     

Do whatever works: A robust approach to fault-tolerant autonomous control

This paper describes a highly distributed fault-tolerant control system capable of compensating for deficiencies in system-level performance even when the cause of a fault cannot be explicitly identified. Developed for an autonomous underwater vehicle that must remain operational for several weeks without human intervention, this system must be capable of dealing with events that cannot be anticipated at design time. A unique aspect of this system is that it handles such events by attempting to do whatever works if it is unable to diagnose and correct specific faults. The software architecture used in this approach is applicable to a wide range of complex autonomous control applications.     

A large-scale study of architectural evolution in open-source software systems

From its very inception, the study of software architecture has recognized architectural decay as a regularly occurring phenomenon in long-lived systems. Architectural decay is caused by repeated, sometimes careless changes to a system during its lifespan. Despite decay’s prevalence, there is a relative dearth of empirical data regarding the nature of architectural changes that may lead to decay, and of developers’ understanding of those changes. In this paper, we take a step toward addressing that scarcity by introducing an architecture recovery framework, ARCADE, for conducting large-scale replicable empirical studies of architectural change across different versions of a software system. ARCADE includes two novel architectural change metrics, which are the key to enabling large-scale empirical studies of architectural change. We utilize ARCADE to conduct an empirical study of changes found in software architectures spanning several hundred versions of 23 open-source systems. Our study reveals several new findings regarding the frequency of architectural changes in software systems, the common points of departure in a system’s architecture during the system’s maintenance and evolution, the difference between system-level and component-level architectural change, and the suitability of a system’s implementation-level structure as a proxy for its architecture.     

Social patterns in productive software development organizations

Software development is a predominantly social activity. It is important to view software development groups, departments, and corporations as social bodies. We study software organizations using a novel data-gathering approach that combines several techniques commonly used in social network analysis. Our techniques differ from those of ordinary social anthropology in that we help the organization introspect about itself; the technique is a mirror for the subject organization. We catalogued social network diagrams using a variety of visualization techniques. We have found visual patterns that correlate well to subjective measures of a good organization. We built analytical models to capture properties of the social networks, employing techniques similar to those used in established social network science. The emerging design technique based on architectural patterns provides a good vehicle for communicating organizational patterns. We have captured practices from outstanding organizations in a group of patterns that form a pattern language for productive software development.     

Architecture and algorithms of the Xphone multimedia communication system

We describe the architecture and the algorithms used in Columbia University'sXphone multimedia communication system. The system assumes a best-effort operating system and network and provides facilities for call management, intra-application scheduling for the support of continuous data flow and integration with the windowing system, and synchronized video/audio acquisition/playback (locally or across a network) with minimized and bounded end-to-end delay. An algorithm based on time-stamps and device-state information is used for synchronization. The effects of jitter (delay variation) are mitigated with silence detection; the end-to-end delay is kept bounded by a restart mechanism. Finally, for live video sources, we describe a source bit-rate adaptation algorithm that maximizes the video image quality to the available network bandwidth and video display window size.     

Modular Robot Motion Planning Using Similarity Metrics

In order for a modular self-reconfigurable robotic system to autonomously change from its current state to a desired one, it is critical to have a cost function (or metric) that reflects the effort required to reconfigure. A reconfiguration sequence can consist of single module motions, or the motion of a branch of modules. For single module motions, the minimization of metrics on the set of sets of module center locations serves as the driving force for reconfiguration. For branch motions, the question becomes which branches should be moved so as to minimize overall effort. Another way to view this is as a pattern matching problem in which the desired configuration is viewed as a void, and we seek branch motions that best fill the void. A precise definition of goodness of fit is therefore required. In this paper, we address the fundamental question of how closely geometric figures can be made to match under a given group of transformations (e.g., rigid-body motions), and what it means to bisect two shapes. We illustrate these ideas in the context of applications in modular robot motion planning.     

Software engineering and production monitoring systems

Software that is to be designed and written for operation in the factory environment is especially difficult to conceptualize, design and successfully install. This paper focuses on some aspects of software engineering that apply to this situation and may prove useful to others involved in this profession. The particular problem that is considered in the paper is that of a Real-time Production Monitoring System although any industrial system could have been used. Monitoring industrial processes and displaying meaning ful data in real-time is extremely difficult, mainly because each component, although complementary, is functionally, electrically and temporally quite different. It is therefore difficult to design a standard factory data structure or always to find elegant processing mechanisms. In order to integrate data from these disparate sources, the system must be carefully architected, using consistent and sound software engineering principles.The paper included practical aspects of the implementation of this particular information system, which is a growing component in the management process of a typical computer-integrated manufacturing facility. The paper contains sections on human-factors engineering, fault detection and system recovery. The selection of the operating system platform is critical, and software engineering professionals should appreciate the sections devoted to the system components. Some material is based on the author's own practical experience gained in the design and implementation of several such systems.     

Parallel geometric algorithms on a mesh-connected computer

We show that a number of geometric problems can be solved on a n × n mesh-connected computer (MCC) inO(n) time, which is optimal to within a constant factor, since a nontrivial data movement on an MCC requires (n) time. The problems studied here include multipoint location, planar point location, trapezoidal decomposition, intersection detection, intersection of two convex polygons, Voronoi diagram, the largest empty circle, the smallest enclosing circle, etc. TheO(n) algorithms for all of the above problems are based on the classical divide-and-conquer problem-solving strategy.This work was supported in part by the National Science Foundation under Grant DCR 8420814. A preliminary version was presented in the 1987 FJCC, Dallas, TX.     

A Dynamic Foundational Architecture for Semantic Web Services

The combination of Web services and ontologies is gaining momentum as the potential silver bullets for tomorrows Web, i.e., the Semantic Web. We propose an architectural foundation for managing semantic Web services in dynamic environments. We introduce the concept of community to cater for an ontological organization of Web services. We develop an ontology called community ontology that serves as a template for describing communities of Web services. We also propose a peer-to-peer approach for managing communities in dynamic environments.