自适应软件：现状与研究挑战

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"这篇《Self-Adaptive Software.pdf》是一篇深入探讨自适应软件的综述文章，重点关注在不断变化的环境中处理分布式应用的软件系统所面临的挑战和研究方向。文章指出，传统的软件开发通常采用开放环结构，这在运行阶段导致了高昂的维护成本和时间消耗，因为需要人工进行重新配置、故障排除等任务。" 正文：自适应软件是为了解决上述问题而提出的解决方案，它是一种闭环系统，具备反馈机制，能够在运行过程中自我调整以应对内部或外部的变化。这些变化可能源自软件系统自身（如故障）或者其运行环境（如用户请求增加）。自适应软件系统的核心能力包括自我监控、环境感知、异常检测以及根据检测到的变化执行相应的适应策略。 1. 自我监控：自适应软件能够持续监测自身的状态和性能指标，这包括系统资源的使用情况、程序的执行效率、错误率等。这种监控能力是系统能够感知自身健康状况并识别潜在问题的关键。 2. 环境感知：除了内部状态，自适应软件还需要理解其运行的外部环境，这可能涉及用户需求、网络条件、硬件资源等。环境感知使得软件能够预测和响应环境变化，从而提供更稳定的服务。 3. 异常检测：通过设定阈值和模式识别，自适应软件可以检测到与正常行为偏离的显著变化，无论是内部错误还是外部冲击。这有助于早期发现并解决潜在问题，防止故障的发生。 4. 适应策略：一旦检测到变化，自适应软件会执行预定义或动态生成的适应策略。这可能包括重新配置、负载均衡、故障隔离、资源调度等，目的是保持系统的高效运作，满足服务质量（QoS）要求。 5. 管理自动化：自适应软件的目标是减少管理复杂性和人为干预，通过自动化手段来实现系统的持续优化。这包括自动修复、动态扩展和收缩、智能资源分配等，极大地提高了软件系统的运维效率。 6. 研究挑战：尽管自适应软件带来诸多好处，但实现这一目标面临许多技术挑战，例如如何设计有效的自我监控机制，如何构建灵活的适应模型，如何确保适应过程的安全性和隐私保护，以及如何在保证性能的同时降低能耗。自适应软件代表了软件工程领域的一个重要发展方向，旨在通过自动化和智能化手段，提升软件在复杂多变环境中的生存能力和服务质量。随着技术的进步，未来自适应软件将在物联网、云计算、边缘计算等场景中发挥更大作用，进一步推动软件系统的智能化和自愈能力。

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M. Salehie and L. Tahvildari

for attributes (e.g., parameters). Moreover, it is essential to determine what

events and attributes have to be monitored to follow up on the changes, and

what resources are essential for adaptation actions?

—Why. This set of questions deals with the motivations of building a self-

adaptive software application. As we discussed before, these questions are

concerned with the objectives addressed by the system (e.g., robustness). If

a goal-oriented requirements engineering approach is adopted to elicit the

requirements, this set of questions identiﬁes the goals of the self-adaptive

software system.

—Who. This set of questions addresses the level of automation and human

involvement in self-adaptive software. With respect to automation, it is ex-

pected that there will be minimum human intervention, whereas an effective

interaction with system owners and managers is required to build trust and

transfer policies (e.g., business policies). This issue will be discussed further

in the taxonomy of adaptation (See Section 3).

—How. One of the important requirements for adaptation is to determine how

the adaptable artifacts can be changed and which adaptation action(s) can be

appropriate to be applied in a given condition? This includes how the order of

changes, their costs and aftereffects are taken into account for deciding the

next action/plan.

In order to realize self-adaptive software, the above questions need to be an-

swered in two phases: a) the developing phase, which deals with developing and

building self-adaptive software either from scratch or by reengineering a legacy

system, and b) the operating phase, which manages the operational concerns

to properly respond to changes in the self/context of a software application.

At the developing phase, designers elicit the requirements based on the above

questions in order to build adaptable software as well as to set up mechanisms

and alternatives to be used at the operating phase. At the operating phase, the

system requires to adapt itself based on these questions. In fact, the questions

in this phase are in general ask about “where” the source of need for a change

is, what needs be changed, and when and how it is better to be changed. the

answer to these questions at the operating phase depends on the approach and

type of adaptation chosen at the developing phase. Some of these questions

may be answered by administrators and managers through policies, and the

rest should be determined by the system itself.

The distinction between the what and where questions is notable. “Where”

addresses which part of the system caused the problem (e.g., deviation from

quality goals), while “what” refers to the attributes and artifacts that need

to be changed to resolve the problem. For example, in a multi-tier enterprise

application, it is essential to know which part caused performance degradation

(e.g., the database tier due to lack of resources) and after that, what needs to

be changed (e.g., changing the service level at the Web tier). Sometimes, the

entity that is the source of change is also the entity that needs to be changed

(e.g., component swapping). Therefore, although these questions are related,

they address different aspects of adaptation.

ACM Transactions on Autonomous and Adaptive Systems, Vol. 4, No. 2, Article 14, Publication date: May 2009.

Self-Adaptive Software: Landscape and Research Challenges

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Fig. 2. Four adaptation processes in self-adaptive software.

2.4 Adaptation Loop

As explained earlier, self-adaptive software embodies a closed-loop mechanism.

This loop, called the adaptation loop, consists of several processes, as well as

sensors and effectors, as depicted in Figure 2. This loop is called the MAPE-K

loop in the context of autonomic computing, and includes the Monitoring,

Analyzing, Planning and Executing functions, with the addition of a shared

Knowledge-base [Kephart and Chess 2003]. Dobson et al. [2006] also represent

the similar loop as autonomic control loop in the context of autonomic commu-

nication, including collect, analyze, decide and act Oreizy et al. [1999] refer to

this loop as adaptation management, which is composed of several processes

for enacting changes and collecting observations, evaluating and monitoring

observations, planning changes, and deploying change descriptions. More de-

tails on the processes, sensors, and effectors of Figure 2 are provided in the

following sections.

2.4.1 Adaptation Processes. The adaptation processes, which exist at the

operating phase, can be summarized as follows:

—The monitoring process is responsible for collecting and correlating data from

sensors and converting them to behavioral patterns and symptoms. This

process partly addresses the where, when, and what questions in the operat-

ing phase. The process can be realized through event correlation, or simply

threshold checking, as well as other methods.

—The detecting process is responsible for analyzing the symptoms provided

by the monitoring process and the history of the system, in order to detect

when a change (response) is required. It also helps to identify where the

source of a transition to a new state (deviation from desired states or goals)

is.

—The deciding process determines what needs to be changed, and how to

change it to achieve the best outcome. This relies on certain criteria to com-

pare different ways of applying the change, for instance by different courses

of action.

—The acting process is responsible for applying the actions determined by the

deciding process. This includes managing nonprimitive actions through pre-

deﬁned workﬂows, or mapping actions to what is provided by effectors and

ACM Transactions on Autonomous and Adaptive Systems, Vol. 4, No. 2, Article 14, Publication date: May 2009.

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