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The goal of this paper is to illustrate how frameworks and patterns address complexities that arise in the design and implementation of high-performance distributed software systems. These complexities are both inherent (e.g., latency reduction and throughput preservation), and accidental (e.g., the continuous reinvention of key concepts and components). This paper explains how complexities occurring in the development of high-performance Web servers can be alleviated with the use of design patterns and object-oriented application frameworks. These techniques were applied to the development our high-performance adaptive Web server framework, JAWS. JAWS exemplifies how a framework can remain flexible without sacrificing performance. 1 Applying Patterns and Frameworks to Web Servers Developers of Web servers strive to build fast, scalable, and configurable systems. This paper describes some common pitfalls encountered by these developers and how to avoid these pitfalls. Common pitfalls include (1) coping with tedious and error-prone low-level programming details, (2) lack of portability, and (3) the complexity of navigating the wide range of server design alternatives. By carefully utilizing patterns and frameworks, these hazards can be avoided, by allowing developers to leverage reuse of design and code. 1.1 Common Pitfalls of Developing Web Server Software Web servers perform the following tasks: connection establishment, service initialization, event demultiplexing, event handler dispatching, interprocess communication, memory management and file caching, static and dynamic component configuration, concurrency, synchronization, and persistence. In most Web servers, these tasks are implemented in an ad hoc manner using low-level native OS application programming interfaces (APIs), such as Win32 or UNIX/POSIX, which are written in C. Unfortunately, native OS APIs are not an effective way to develop Web servers or other types of communication middleware and applications [1]. The following are common pitfalls associated with the use of native OS APIs: Excessive low-level details: Building Web servers with native OS APIs requires developers to have intimate knowledge of low-level OS details. Developers must carefully track which error codes are returned by each system call and handle these OS-specific problems in their servers. Such details divert attention from the broader, more strategic issues, such as protocol semantics and server structure. For example, UNIX developers who use the wait system call must distinguish between return errors due to no child processes being present and errors from signal interrupts. In the latter case, the wait must be reissued. Reinvention of incompatible programming abstractions: A common remedy for the excessive level of detail with OS APIs is to define higher-level programming abstractions. For instance, many Web servers create a file cache to avoid accessing the filesystem for each client request. However, these types of abstractions are often rediscovered and reinvented independently by each developer or project. This ad hoc devel

Software quahty is achieved through the apphcatlon of development techniques and the use of verification procedures throughout the development process Careful consideratmn of specific quality attmbutes and validation reqmrements leads to the selection of a balanced collection of review, analysis, and testing techmques for use throughout the life cycle. This paper surveys current verification, validation, and testing approaches and discusses their strengths, weaknesses, and life-cycle usage. In conjunction with these, the paper describes automated tools used to nnplement vahdation, verification, and testmg. In the discussion of new research thrusts, emphasis is gwen to the continued need to develop a stronger theoretical basis for testing and the need to employ combinations of tools and techniques that may vary over each apphcation.

Networking research often relies on simulation in order to test and evaluate new ideas. An important requirement of this process is that results must be reproducible so that other researchers can replicate, validate, and extend existing work. We look at the landscape of simulators for research in peer-to-peer (P2P) networks by conducting a survey of a combined total of over 280 papers from before and after 2007 (the year of the last survey in this area), and comment on the large quantity of research using bespoke, closed-source simulators. We propose a set of criteria that P2P simulators should meet, and poll the P2P research community for their agreement. We aim to drive the community towards performing their experiments on simulators that allow for others to validate their results.

Analgorithm componentis an implementation of an algorithm which is not intended to be a stand-alone module, but to perform a specific task within a large software package or even within several distinct software packages. Therefore, the design of algorithm components must also incorporate software-engineering aspects. A key design goal is adaptability. This goal is important for maintenance throughout a project, prototypical development, and reuse in new, unforseen contexts. From a theoretical viewpoint most algorithms apply to a range of possible use scenarios. Ideally, each algorithm is implemented by one algorithm component, which is easily, safely, and efficiently adaptable to all of these contexts.Various techniques have been developed for the design and implementation of algorithm components. However, a common basis for systematic, detailed evaluations and comparisons in view of therealpractical needs is still missing. Basically, this means a set of concrete criteria, which specify what sort of adaptability isreallyrequired in practice, and which are well-justified by convincing, representative use scenarios.This paper is intended to be a first “milestone” on the way towards such a system of criteria. We will present a set of concrete goals, which are general and problem-independent and might appear ubiquitously in the algorithmic realm. These goals are illustrated, motivated, and justified by an extensive requirements analysis for a particular algorithm from a particular algorithmic domain: Dijkstra's algorithm for shortest paths in networks.Clearly, the field of algorithmics might be too versatile to allow a comprehensive, yet concise set of precise, justified criteria. Even a domain as restricted as graph and network algorithms includes aspects that are not fully understood. The analysis will include a discussion of the limits of the case study and the scope of the goals. The case study was chosen because it seems to be close to the “boderline” between the aspects that are well understood and the aspects that are not. Hence, this example may well serve as an“acid test” for programming techniques in view of the state of the art.

This paper has provided an overview of the field of object-oriented programming. After presenting a historical perspective and some major achievements in the field, four research directions were introduced: technologies integration, software components, distributed programming, and new paradigms. In general there is a need to continue research in traditional areas: (1) as computer systems become more and more complex, there is a need to further develop the work on architecture and design; (2) to support the development of complex systems, there is a need for better languages, environments, and tools; (3) foundations in the form of the conceptual framework and other theories must be extended to enhance the means for modeling and formal analysis, as well as for understanding future computer systems.

One of the most natural, elegant, and efficient mechanisms for synchronization and communication, especially for systems with shared memory, is the monitor . Over the past twenty years many kinds of monitors have been proposed and implemented, and many modern programming languages provide some form of monitor for concurrency control. This paper presents a taxonomy of monitors that encompasses all the extant monitors and suggests others not found in the literature or in existing programming languages. It discusses the semantics and performance of the various kinds of monitors suggested by the taxonomy, and it discusses programming techniques suitable to each.

Software reuse is the process of creating software systems from existing software rather than building software systems from scratch. This simple yet powerful vision was introduced in 1968. Software reuse has, however, failed to become a standard software engineering practice. In an attempt to understand why, researchers have renewed their interest in software reuse and in the obstacles to implementing it. This paper surveys the different approaches to software reuse found in the research literature. It uses a taxonomy to describe and compare the different approaches and make generalizations about the field of software reuse. The taxonomy characterizes each reuse approach in terms of its reusable artifacts and the way these artifacts are abstracted, selected, specialized, and integrated . Abstraction plays a central role in software reuse. Concise and expressive abstractions are essential if software artifacts are to be effectively reused. The effectiveness of a reuse technique can be evaluated in terms of cognitive distance —an intuitive gauge of the intellectual effort required to use the technique. Cognitive distance is reduced in two ways: (1) Higher level abstractions in a reuse technique reduce the effort required to go from the initial concept of a software system to representations in the reuse technique, and (2) automation reduces the effort required to go from abstractions in a reuse technique to an executable implementation. This survey will help answer the following questions: What is software reuse? Why reuse software? What are the different approaches to reusing software? How effective are the different approaches? What is required to implement a software reuse technology? Why is software reuse difficult? What are the open areas for research in software reuse?

Frameworks are the key to successful object-oriented application development. The goal of this paper is to show that successful framework development must match the business domains they are derived from, and that they must be flexible enough to evolve gracefully. Our principal contribution is the presentation of concepts that can be used for domain partitioning and framework layering in order to overcome difficulties in framework construction and layering. The work reported here is based on a series of object-oriented banking projects. The system, including several frameworks, consists of 3500 C++-classes and was developed over the past five years.

Most of the publications on frameworks describe them as tools for optimizing the design and implementation of complex software [Fayad and Schmidt 1997]. This paper presents another point of view: Framework concepts for enabling tailorability through the user of the application. We will use the application domain of Computer Supported Cooperative Work (CSCW) because the need for tailorability can be easily demonstrated here. While tailorability is also an issue outside the scope of CSCW, the special demands of support for cooperative work make it a critical issue for groupware. Thus, tailoring of groupware raises several questions, which in the mainstream adaptability discussion are not (and do not have to be) addressed { at least not to the degree necessary in CSCW [Stiemerling and Cremers 1998].

Coclea, Rovereto, ItalySherlock is a domain analysis methodology for the extraction of reusable frameworks. Sherlockis based both on Proteus and on FODA domain analysis techniques. The input of Sherlock is adescription of the domain based on domain applications, literature, user requirements, andinterviews with domain and market experts. The output of Sherlock is a framework comprising aset of components organized in architectures. In this paper we describe the main features ofSherlock and present a case study regarding the development of a graphic user interfaceframework for business and management information systems.

Collaborative environments have grown quite sophisticated over the years. They have evolved from simple text conferencing tools [2] to full suites of integrated multi-modal tools such as Habanero [9] or MITRE's room-based Collaborative Virtual Workspace [3, 4]. As a result, evaluating multi-modal collaborative systems is an order of magnitude more complex than single-user, single-application HCI evaluation. In the context of the DARPA Intelligent Collaboration &Visualization (IC&V) program, the MITRE HCI group has adapted its logging technology to the task of evaluating collaborative systems. The MITRE Multi-Modal Logger (MML) is a system for recording, retrieving, annotating, and visualizing data. In this paper, we describe the capabilities of the MML and its application to research including the IC&V Evaluation Working Group's work [5, 6, 7, 8, 13].

Interest is increasing in the transformational approach to programming and in mechanical aids for supporting the program development process. Available aids range from simple editorlike devices to rather powerful interactive transformation systems and even to automatic synthesis tools. This paper reviews and classifies transformation systems and is intended to acquaint the reader with the current state of the art and provide a basis for comparing the different approaches. It is also designed to provide easy access to specific details of the various methodologies.