系统是什么？

摘自《FUNDAMENTALS OF PHYSICAL GEOGRAPHY (2nd Edition)》 BY ？

刘建文略译（http://blog.csdn.net/keminlau ）

KEY: 科学哲学 系统 系统理论 模型

系统与模型
(a). Humans and Their Models

One common conclusion of scientific inquiry（质询; 调查 ） is that the world of nature is often very complex. To understand this complexity, scientists usually try to envisage（想像, 设想;） the phenomena of nature as simplified versions of reality known as a system. A system can be defined as a collection of interrelated parts that work together by way of some driving（精力旺盛的; 强劲的; 驱使的 ） process.

我们对自然界进行研究的一个常见的结论就是，自然界是很复杂的。为了把握这些复杂性，科学家通常把自然现象假想成一种简化过的实在（reality），它就是我们常常听到的“系统”。“系统”可以被定义成相关部分（或者叫子系统）的集合，这些子部分在某种驱束力下工作在一起。

In the world of science, the word model is quite similar in meaning to the term system. Models in science tend to be simplified representations of reality that can be explained of mathematically and through the use of graphics. The following graphical model is used to help explain the processes involved in scientific understanding. The arrows in this graphically model suggest a continuous interaction between perceptible（可察觉的, 看得见的） phenomena and theory through the processes of explanation and validation. This simple graphical model, while an extreme abstraction of the real world, is quite useful in explaining how scientific understanding works.

在科学的世界里，“模型”一词与“系统”有十分相似的意思，只是二者偏重有点不一样。模型偏向于简化实在的表征，从而有助于数学地或图形化地对实在进行解释（explained）。比如下面的图形模型，它是用来帮助解释科学认识（scientific understanding）的过程的模型。在这幅生动的模型图中，箭头有形地展示（suggest）了透过解释和验证的过程在理论（theory）与现象（phenomena）之间存在的连续不断的交互。这也是科学认识的本质过程。这幅相当抽象的构图很简单，但对于解释科学认识的原理很有用。
KEMIN：没有讲“系统”偏向简化实在的什么东西。

Figure 4a-1: The general relationship between perceptible phenomena and theory using scientific method for understanding. The interaction between perceptible phenomena and theory is arrived at through the processes of explanation and validation.

In Physical Geography, and many other fields of knowledge, systems and models are used extensively as aids in explaining natural phenomena around us.

在各知识领域里，系统和模型被广泛地用来辅助解释我们身边的各种自然现象。

系统的定义
(b). Definitions of Systems and Models

As suggested in the previous section, a system is a assemblage of interrelated parts that work together by way of some driving process (see Figure 4b-1). Systems are often visualized or modeled as component blocks that have connections drawn between them. For example, the illustration below describes the interception（拦截; 截击; 截取;） of solar radiation（太阳辐射） by the Earth. In this system, the Earth and Sun, the parts or component blocks, are represented by two colored circles of different size. The process of solar emission（发射） and the interception of the Sun's emitted radiation by the Earth (the connection) is illustrated by the drawn lines.

前面谈到，系统是一组相关部分的集合，并且这些子部分在某种驱束力下一起工作。系统常常被可视化或模型化为多个组件块，并且在这些组件块之间用线连起来表示它们的关系。比如如下的关于太阳辐射的模型图：

Figure 4b-1: Simple visual model of solar radiation being emitted from the Sun and intercepted by the Earth.

Most systems share the same common characteristics. These common characteristics include the following:

大多数系统都拥有一些通用的性质，包括如下的：

• 1. Systems have a structure that is defined by its parts and processes.
• 2. Systems are generalizations of reality.
• 3. Systems tend to function in the same way. This involves the inputs and outputs of material (energy and/or matter) that is then processed causing it to change in some way.
• 4. The various parts of a system have functional as well as structural relationships between each other.
• 系统都是有一定的结构，由组成部分和作用（processes）定义；
• 系统都是对实在（reality）的一般化（generalizations ）；
• 系统都有同样的表现作用的方式，作用过程包括物质和能量的输入与输出，由输入到输出，物质和能量会以某一种方式被改变或转换；
• 系统内部各部分都有功能依赖和结构制约关系；
• 5. The fact that functional relationships exist between the parts suggests the flow and transfer of some type of energy and/or matter.
• 6. Systems often exchange energy and/or matter beyond their defined boundary with the outside environment, and other systems, through various input and output processes.
• 7. Functional relationships can only occur because of the presence of a driving force（驱动力，张力）.
• 8. The parts that make up a system show some degree of integration - in other words the parts work well together.
• 系统内两部分间有功能关系意味着它们之间存在着某种能量和物质的流动和传输；
• 系统通常会与定义它的边界以外的环境（包括其它系统）进行能量或物质交换；
• 功能关系只源于某种驱动力或张力的存在；
• 系统内的各部分表现出一定的集成程度，并且系统整体大于部分之和。
  
  KEMIN:最后一点原文不好理解；还有这里能量和物质还没有进一步解开。

Within the boundary of a system we can find three kinds of properties:

Elements - are the kinds of parts (things or substances) that make up a system. These parts may be atoms or molecules（分子; 些微）, or larger bodies of matter like sand grains, rain drops, plants, animals, etc.

Attributes - are characteristics of the elements that may be perceived（察觉; 意识到; 感知; 理解） and measured. For example: quantity, size, color, volume, temperature, and mass.

Relationships - are the associations that occur between elements and attributes. These associations are based on cause and effect.

在系统的边界内我们可找到三类属性：

元素（Elements）：组成系统的各种部分（东西或事物）。这些系统部分可能是原子性，也可能是非原子性，比如子系统；

属性（Attributes）：指被丈量或感知的系统元素的特性（characteristics）；比如数量、大小、颜色、容量、温度和规模；

关系（Relationships）：指在元素和属性之间存在的某种结合（associations），这些结合是基于因果关系的。

We can define the state of the system by determining the value of its properties (the elements, attributes, and/or relationships).

我们可以根据这三类属性的值（value）来定义或描述一个系统（的状况）。

系统的分类

Scientists have examined and classified many types of systems. Some of the classified types include:

Isolated System - a system that has no interactions beyond its boundary layer. Many controlled laboratory experiments are this type of system.

Closed System - is a system that transfers energy, but not matter, across its boundary to the surrounding environment . Our planet is often viewed as a closed system.

Open System - is a system that transfers both matter and energy can cross its boundary to the surrounding environment. Most ecosystems生态系统 are example of open systems.

Morphological（形态学的; 形态的） System - this is a system where we understand the relationships between elements and their attributes in a vague sense based only on measured features or correlations. In other words, we understand the form or morphology a system has based on the connections between its elements. We do not understand exactly how the processes work to transfer energy and/or matter through the connections between the elements.

Cascading System - this is a system where we are primarily interested in the flow of energy and/or matter from one element to another and understand the processes that cause this movement. In a cascading system, we do not fully understand quantitative relationships that exist between elements related to the transfer of energy and/or matter.

Process-Response System - this is a system that integrates the characteristics of both morphological and cascading systems. In a process-response system, we can model the processes involved in the movement, storage, and transformation of energy and/or matter between system elements and we fully understand how the form of the system in terms of measured features and correlations.

Control System - a system that can be intelligently manipulated by the action of humans.

Ecosystem - is a system that models relationships and interactions between the various biotic and abiotic components making up a community or organisms and their surroundng physical environment.

能量与环境

An environmental system can be defined as a system where life interacts with abiotic factors. All environmental systems involve the capture, movement, storage, and use of energy. This fact also makes them energy systems. Energy is captured in the living components of environmental systems by processes like photosynthesis, biomass consumption, and biotic decomposition. Energy is also used in environmental processes that are strictly abiotic. For example, solar energy is responsible for wind, weathering, and precipitation.

平衡与反馈

Equilibrium can be defined as the average state of a system as measured through one of its attributes or elements. Scientists have defined six different types of equilibrium. Most systems maintain a steady state equilibrium through the operation of positive and negative feedback mechanisms. Negative-feedback mechanisms control the state of the system by dampening or reducing the size of the system's elements or attributes. Positive-feedback mechanisms feed or increase the size of one or more of the system's elements or attributes over time. This section concludes by showing how negative and positive feedbacks work to cause fluctuations in the population size of aphids.