Aspect] is a simple and practical aspect-oriented extension to Java With just a few new constructs, AspectJ provides support for modular implementation of a range of crosscutting concerns. In AspectJ's dynamic join point model, join points are well-defined points in the execution of the program; pointcuts are collections of join points; advice are special method-like constructs that can be attached to pointcuts; and aspects are modular units of crosscutting implementation, comprising pointcuts, advice, and ordinary Java member declarations. AspectJ code is compiled into standard Java bytecode. Simple extensions to existing Java development environments make it possible to browse the crosscutting structure of aspects in the same kind of way as one browses the inheritance structure of classes. Several examples show that AspectJ is powerful, and that programs written using it are easy to understand.

An overview of AspectJ

Service-oriented architectures (SOA) is an emerging approach that addresses the requirements of loosely coupled, standards-based, and protocol- independent distributed computing. Typically business operations running in an SOA comprise a number of invocations of these different components, often in an event-driven or asynchronous fashion that reflects the underlying business process needs. To build an SOA a highly distributable communications and integration backbone is required. This functionality is provided by the Enterprise Service Bus (ESB) that is an integration platform that utilizes Web services standards to support a wide variety of communications patterns over multiple transport protocols and deliver value-added capabilities for SOA applications. This paper reviews technologies and approaches that unify the principles and concepts of SOA with those of event-based programing. The paper also focuses on the ESB and describes a range of functions that are designed to offer a manageable, standards-based SOA backbone that extends middleware functionality throughout by connecting heterogeneous components and systems and offers integration services. Finally, the paper proposes an approach to extend the conventional SOA to cater for essential ESB requirements that include capabilities such as service orchestration, "intelligent" routing, provisioning, integrity and security of message as well as service management. The layers in this extended SOA, in short xSOA, are used to classify research issues and current research activities.

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Service oriented architectures: approaches, technologies and research issues

[서평]「Component Software」 - Beyond Object-Oriented Programming -

In advanced service oriented systems, complex applications, described as abstract business processes, can be executed by invoking a number of available Web services. End users can specify different preferences and constraints and service selection can be performed dynamically identifying the best set of services available at runtime. In this paper, we introduce a new modeling approach to the Web service selection problem that is particularly effective for large processes and when QoS constraints are severe. In the model, the Web service selection problem is formalized as a mixed integer linear programming problem, loops peeling is adopted in the optimization, and constraints posed by stateful Web services are considered. Moreover, negotiation techniques are exploited to identify a feasible solution of the problem, if one does not exist. Experimental results compare our method with other solutions proposed in the literature and demonstrate the effectiveness of our approach toward the identification of an optimal solution to the QoS constrained Web service selection problem

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Adaptive Service Composition in Flexible Processes

We may not be able to make you love reading, but production workflow concepts and techniques will lead you to love reading starting from now. Book is the window to open the new world. The world that you want is in the better stage and level. World will always guide you to even the prestige stage of the life. You know, this is some of how reading will give you the kindness. In this case, more books you read more knowledge you know, but it can mean also the bore is full.

Production workflow: concepts and techniques

A holy grail of component-based software engineering is write-once, reuse everywhere. However, in modern distributed, component-based systems supporting emerging application areas such as service-oriented e-business (where Web services are viewed as components) and peer-to-peer computing, this is difficult. Non-functional requirements (related to quality-of-service (QoS) issues such as security, reliability, and performance) vary with deployment context, and sometimes even at run-time, complicating the task of re-using components. In this paper, we present a middleware-based approach to managing dynamically changing QoS requirements of components. Policies are used to advertise non-functional capabilities and vary at run-time with operating conditions. We also provide middleware enhancements to match, interpret, and mediate QoS requirements of clients and servers at deployment time and/or runtime.

http://www.cs.ucdavis.edu/~devanbu/icse2004-gq.pdf

GlueQoS: middleware to sweeten quality-of-service policy interactions

Service-oriented computing is emerging as a distributed computing model where autonomous services interact with each other using standard Internet technology. In addition to the application-specific functions that services provide (different) services may also support (different) sets of protocols and formats addressing extra-functional concerns such as transaction processing and reliable messaging. This raises the need for services to complement their functional service descriptions with descriptions of extra-functional capabilities, requirements, and/or preferences, which must be matched and enforced for service interactions. In this paper, we address the problem of transactional coordination in service-oriented computing. We argue for the use of declarative policy assertions to advertise and match support for different transaction styles (direct transaction processing, queued transaction processing, and compensation-based transaction processing), and introduce the concept of and system support for transaction coupling modes as the policy-based contracts guiding transactional business process execution. We focus on concrete, protocol-specific policies that apply to relevant Web services specifications. Using transaction policies and our middleware system, we are able to support a reliable SOC environment.

Transaction policies for service-oriented computing

Some "non-" or "extra-functional" features, such as reliability, security, and tracing, defy modularization mechanisms in programming languages. This makes such features hard to design, implement, and maintain. Implementing such features within a single platform, using a single language, is hard enough With distributed, heterogeneous (DH) systems, these features induce complex implementations which cross-cut different languages, OSs, and hardware platforms, while still needing to share data and events. Worse still, the precise requirements for such features are often locality-dependent and discovered late (e.g., security policies). The DADO/sup 1/ approach helps program cross-cutting features by improving DH middleware. A DADO service comprises pairs of adaplets which are explicitly modeled in IDL. Adaplets may be implemented in any language compatible with the target application, and attached to stubs and skeletons of application objects in a variety of ways. DADO supports flexible and type-checked interactions (using generated stubs and skeletons) between adaplets and between objects and adaplets. Adaplets can be attached at run-time to an application object. We describe the approach and illustrate its use for several cross-cutting features, including performance monitoring, caching, and security. We also discuss software engineering process, as well as run-time performance implications.

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DADO: enhancing middleware to support crosscutting features in distributed, heterogeneous systems

Due to the increasing complexity of web applications and emerging HTML5 standards, a large amount of runtime state is created and managed in the user's browser. While such complexity is desirable for user experience, it makes it hard for developers to implement mechanisms that provide users ubiquitous access to the data they create during application use. This paper presents our research into browser session migration for JavaScript-based web applications. Session migration is the act of transferring a session between browsers at runtime. Without burden to developers, our system allows users to create a snapshot image that captures all runtime state needed to resume the session elsewhere. Our system works completely in the JavaScript layer and thus snapshots can be transfered between different browser vendors and hardware devices. We report on performance metrics of the system using five applications, four different browsers, and three different devices.

/pdf/imagen-runtime-migration-of-browser-sessions-for-javascript-2ytcly76wu.pdf

Imagen: runtime migration of browser sessions for javascript web applications

Design rules express constraints on the behavior and structure of a program. These rules can help ensure that a program follows a set of established practices, and avoids certain classes of errors.Design rules often crosscut program structure and enforcing them is emerging as an important application domain for Aspect Oriented Programming. For many interesting design rules, current general purpose AOP languages lack the expressiveness to characterize them statically and enforce them at compile time.We have developed a domain specific language called Program Description Logic (PDL). PDL allows succinct declarative definitions of programmatic structures which correspond to design rule violations. PDL is based on a fully static and expressive pointcut language. PDL pointcuts allow characterizing a wide range of design rules without sacrificing static verification.We evaluate PDL by comparing it to FxCop, an industrial strength tool for checking design rules.

/pdf/a-static-aspect-language-for-checking-design-rules-4wh1bxatkb.pdf

Eric Wohlstadter

Papers

GlueQoS: middleware to sweeten quality-of-service policy interactions

Transaction policies for service-oriented computing

DADO: enhancing middleware to support crosscutting features in distributed, heterogeneous systems

Imagen: runtime migration of browser sessions for javascript web applications

A static aspect language for checking design rules