Concept of the system

We live in a world that consists of many different objects that have a variety of different properties and interacting with each other. For example, the objects of the surrounding world are planets solar system, which have different properties (mass, geometric dimensions, etc.) and interact with the Sun and each other according to the law of universal gravitation.

Each planet is part of a larger object - the Solar System, which in turn is part of the Galaxy. At the same time, each planet consists of different atoms chemical elements, which consist of elementary particles. Thus, in fact, each object can consist of a collection of other objects, i.e. forms a system.

An important feature of the system is its holistic functioning. A system is not a set of individual elements, but a collection of interconnected elements. For example, Personal Computer is a system that consists of various devices, which are interconnected both hardware (physically connected to each other) and functionally (exchange information).

Definition 1

A system is a collection of interconnected objects, which are called system elements.

Note 1

Each system has its own structure, which is characterized by the composition and properties of the elements, their relationships and connections with each other. The system is able to maintain its integrity under the influence of various external factors and internal changes as long as its structure remains unchanged. If the structure of the system changes (for example, when one of its elements is removed), it may cease to function as a single whole. For example, if you remove one of the computer devices (for example, the motherboard), the computer will stop working, that is, it will stop functioning as a system.

The main provisions of systems theory appeared during the study dynamic systems and their functional elements. A system is a group of interconnected elements that act together to accomplish a predetermined task. Using systems analysis, you can determine the most real ways fulfillment of the assigned task, which ensure maximum satisfaction of the stated requirements.

The elements that form the basis of systems theory are not created through hypotheses, but are obtained experimentally. To start building a system you need to have general characteristics technological processes, which are also necessary when creating mathematically formulated criteria that a process or its theoretical description must satisfy. The modeling method is one of the most important methods of scientific research and experimentation.

Systems approach

To build models of objects, a systems approach is used, which is a methodology for solving complex problems. This methodology is based on considering an object as a system that operates in a certain environment. Systems approach allows you to reveal the integrity of an object, identify and study its internal structure, as well as connections with the external environment. In this case, the object is a part of the real world, which is isolated and studied in connection with the problem being solved in constructing a model. In addition, when using a systems approach, a consistent transition from the general to the specific is assumed, which is based on consideration of the design goal, and the object is considered in connection with environment.

A complex object can be divided into subsystems, which are parts of the object and satisfy the following requirements:

1. subsystem is a functionally independent part of an object that is connected to other subsystems and exchanges information and energy with them;
2. each subsystem may have functions or properties that do not coincide with the properties of the entire system;
3. each of the subsystems can be divided down to the element level.

Here, an element is understood as a lower-level subsystem, which further division does not seem appropriate from the perspective of the problem being solved.

Note 2

Thus, the system is represented as an object consisting of a set of subsystems, elements and connections for its creation, research or improvement. In this case, the enlarged representation of the system, which includes the main subsystems and connections between them, is called macrostructure, and detailed consideration internal structure systems down to the level of elements - microstructure.

The concept of a system is usually associated with the concept of a supersystem - a system of more high level, which includes the object in question, and the function of any system can be determined only through the supersystem. Also important is the concept of the environment - a set of objects in the external world that significantly influence the efficiency of the system, but are not part of the system and its supersystem.

In a systems approach to building models, the concept of infrastructure is used, which describes the relationship of the system with its environment (environment).

Isolating, describing and studying the properties of an object that are essential for a specific task is called object stratification.

With a systems approach to modeling, it is important to determine the structure of the system, which is defined as a set of connections between system elements that reflect their interaction.

There are structural and functional approach to modeling.

At structural approach the composition of the selected elements of the system and the connections between them are determined. The set of elements and connections makes up the structure of the system. Typically, a topological description is used to describe the structure, which makes it possible to identify the component parts of the system and determine their connections using graphs.

Less commonly used is a functional description, which considers individual functions - algorithms for system behavior. In this case, a functional approach is implemented, which defines the functions performed by the system.

With a systems approach, different sequences of model development are possible based on two main design stages: macro-design and micro-design. At the macro-design stage, a model of the external environment is built, resources and limitations are identified, a system model and criteria for assessing adequacy are selected.

The micro-design stage depends on the type of model chosen. This stage involves the creation of information, mathematical, technical or software modeling systems. When microdesigning, the basic specifications created model, estimate the time it takes to work with it and the cost of resources to obtain the required quality of the model.

When building a model, regardless of its type, it is necessary to adhere to the principles of a systematic approach:

1. consistently move through the stages of creating a model;
2. coordinate information, resource, reliability and other characteristics;
3. correctly correlate different levels of model construction;
4. adhere to the integrity of the individual stages of model design.

Static information models

Any system continues to exist in space and time. At different points in time, the system is determined by its state, which describes the composition of the elements, the values ​​of their properties, the magnitude and nature of the interaction between the elements, etc.

For example, the state of the Solar system at certain points in time is described by the composition of the objects that are included in it (the Sun, planets, etc.), their properties (size, position in space, etc.), the magnitude and nature of their interaction (gravitational force, electromagnetic waves and etc.).

Models that describe the state of a system at a certain point in time are called static information models.

For example, in physics, static information models are models that describe simple mechanisms, in biology - models of the structure of plants and animals, in chemistry - models of the structure of molecules and crystal lattices etc.

Dynamic information models

The system can change over time, i.e. there is a process of change and development of the system. For example, when the planets move, their position relative to the Sun and among themselves changes; changes chemical composition Sun, radiation, etc.

Models that describe the processes of change and development of systems are called dynamic information models.

For example, in physics, dynamic information models describe the movement of bodies; in chemistry, the processes of passage chemical reactions, in biology - the development of organisms or animal species, etc.

Classic approach to model building- the approach to studying the relationships between individual parts of the model involves considering them as a reflection of the connections between individual subsystems of the object. This (classical) approach can be used to create quite simple models.

Thus, developing a model M based on the classical approach means summing up individual components into a single model, with each component solving its own problems and isolated from other parts of the model. Therefore, the classical approach can be used to implement relatively simple models in which it is possible to separate and mutually independent consider individual aspects of the functioning of a real object.

Two distinctive aspects of the classical approach can be noted:

There is a movement from the particular to the general,

The created model is formed by summing up its individual components and does not take into account the emergence of a new systemic effect.

Systems approach- this is an element of the doctrine of the general laws of development of nature and one of the expressions of the dialectical doctrine.

With a systematic approach to modeling systems, it is necessary first of all to clearly define the purpose of the modeling. Since it is impossible to completely simulate a really functioning system, a model (model system, or second system) is created for the problem at hand. Thus, in relation to modeling issues, the goal arises from the required modeling tasks, which allows one to approach the selection of a criterion and evaluate which elements will be included in the created model M. Therefore, it is necessary to have a criterion for selecting individual elements into the created model.

It is important for the systems approach to determine the structure of the system - the set of connections between the elements of the system, reflecting their interaction.

The systems approach allows us to solve the problem of building a complex system, taking into account all factors and possibilities, proportional to their significance, at all stages of studying the system S and building the model M.

The systems approach means that each system S is an integrated whole even when it consists of separate disconnected subsystems. Thus, the basis of the systems approach is the consideration of the system as an integrated whole, and this consideration during development begins with the main thing - the formulation of the purpose of operation.

With a structural approach the composition of the selected elements of the system S and the connections between them are revealed. The set of elements and connections between them allows us to judge the structure of the system. The latter, depending on the purpose of the study, can be described at different levels of consideration. Most general description structure is a topological description that allows you to determine in the most general concepts components of the system and well formalized on the basis of graph theory.

With a functional approach individual functions are considered, i.e., algorithms for the behavior of the system, and a functional approach is implemented that evaluates the functions that the system performs, and a function is understood as a property that leads to the achievement of a goal. Since a function reflects a property, and a property reflects the interaction of a system S with the external environment E, the properties can be expressed in the form of either some characteristics of the elements Si(j) and subsystems Si, - the system, or the system S as a whole.

The main stages of assessing complex systems.

Stage 1. Determining the purpose of the assessment. IN system analysis There are two types of goals. A qualitative goal is a goal, the achievement of which is expressed on a nominal scale or on an order scale. Quantitative is a goal, the achievement of which is expressed in quantitative scales.

Stage 2. Measuring properties of a system that are considered significant for evaluation purposes. To do this, appropriate scales for measuring properties are selected and all studied properties of systems are assigned a certain value on these scales.

Stage 3. Justification of preferences for quality criteria and performance criteria for systems based on properties measured on selected scales.

Stage 4. The actual assessment. All systems under study, considered as alternatives, are compared according to formulated criteria and, depending on the evaluation purposes, are ranked, selected, and optimized.

When modeling systems, two approaches are used: classical (inductive), which developed historically first, and systemic, which has been developed recently.

Classic approach. Historically, the classical approach to studying an object and modeling a system was the first to emerge. The classical approach to synthesizing a system model (M) is presented in Fig. 3. The real object to be modeled is divided into subsystems, initial data (D) for modeling are selected and goals (T) are set, reflecting individual aspects of the modeling process. Based on a separate set of source data, the goal of modeling a separate aspect of the system’s functioning is set; on the basis of this goal, a certain component (K) is formed future model. A set of components is combined into a model.

That. the components are summed up, each component solves its own problems and is isolated from other parts of the model. We apply the approach only for simple systems, where the relationships between components can be ignored. Two distinctive aspects of the classical approach can be noted:

1. there is a movement from the particular to the general when creating a model;

2. the created model (system) is formed by summing up its individual components and does not take into account the emergence of a new systemic effect.

Rice. 3. Classical approach to constructing an object and studying the model

Systems approach – a methodological concept based on the desire to build complete picture the object being studied, taking into account the elements of the object that are important for the problem being solved, the connections between them and external relations with other objects and the environment. With the increasing complexity of modeling objects, the need arose to observe them from a higher level. In this case, the developer considers this system as some subsystem of a higher rank. For example, if the task is to design a monitoring system for a separate object, then from the perspective of a systems approach we must not forget that this system is integral part some complex. The basis of the systems approach is the consideration of the system as an integrated whole, and this consideration during development begins with the main thing - the formulation of the purpose of operation. In Fig. 4. The process of synthesizing a system model based on a systems approach is conventionally presented. It is important for the systems approach to determine the structure of the system - the set of connections between the elements of the system, reflecting their interaction.

Rice. 4. Systematic approach to constructing an object and studying the model

There are structural and functional approaches to studying the structure of a system and its properties. With a structural approach, the composition of the selected elements of the system and the connections between them are revealed. In the functional approach, algorithms for the behavior of the system are considered (functions are properties that lead to the achievement of a goal).

Control questions to section 2

1. What is determined during the system analysis process?

2. What is determined in the process of system synthesis?

3. How is the effectiveness of the system assessed?

4. What is meant by optimal system?

5. Properties inherent in a complex system and their brief description.

6. What is the problem of choosing the level of detail of models?

7. List the main stages of system modeling.

Currently, in the analysis and synthesis of complex (large) systems, a systems approach has been developed, which differs from the classical (or inductive) approach. Classic approach examines the system by moving from the particular to the general and synthesizes (constructs) the system by merging its components, developed separately. In contrast to this systems approach involves a consistent transition from the general to the specific, when the basis of consideration is the goal, and the object under study is distinguished from the environment.

Simulation object. Specialists in the design and operation of complex systems deal with control systems at various levels that have common property- the desire to achieve some goal. We will take this feature into account in the following definitions of the system.

System or object S- a purposeful set of interconnected elements of any nature.

External environment E- a set of elements of any nature existing outside the system that influence the system or are under its influence.

Depending on the purpose of the study, different relationships between the object S itself and the external environment E can be considered. Thus, depending on the level at which the observer is located, the object of study can be distinguished in different ways and different interactions of this object with the external environment can take place.

With the development of science and technology, the object itself is continuously becoming more complex, and now they are talking about the object of research as some complex system that consists of various components interconnected with each other. Therefore, considering the systems approach as the basis for building large systems and as a basis for creating a methodology for their analysis and synthesis, it is first of all necessary to define the very concept of a systems approach.

Systems approach- this is an element of the doctrine of the general laws of development of nature and one of the expressions of the dialectical doctrine. With a systematic approach to modeling systems, it is necessary first of all to clearly define the purpose of the modeling. Since it is impossible to completely simulate a really functioning system (the original system, or the first system), a model (the model system, or the second system) is created for the problem at hand.

Thus, in relation to modeling issues, the goal arises from the required modeling tasks, which allows one to approach the selection of a criterion and evaluate which elements will be included in the created model M. Therefore, it is necessary to have a criterion for selecting individual elements into the created model.

Approaches to systems research. It is important for the systems approach to determine system structure- a set of connections between elements of the system, reflecting their interaction. Structure systems can be studied

1. from outside from the point of view of the composition of individual subsystems and the relationships between them,

2. and from the inside, when individual properties are analyzed that allow the system to achieve a given goal, i.e. when the functions of the system are studied.

In accordance with this, a number of approaches have been outlined to the study of the structure of a system with its properties, which should first of all include structural approach And functional approach.

At structural approach the composition of the selected elements of the system S and the connections between them are revealed. The set of elements and connections between them allows us to judge the structure of the system. The latter, depending on the purpose of the study, can be described at different levels of consideration. The most general description of the structure is a topological description, which allows one to define the constituent parts of the system in the most general terms and is well formalized on the basis of graph theory.

Less common is functional description, when individual functions are considered, i.e., system behavior algorithms, and implemented functional approach, which evaluates the functions that the system performs, whereby a function is understood as a property that leads to the achievement of a goal. Since a function displays a property, and a property reflects the interaction of the system S with the external environment E, the properties can be expressed in the form of either some characteristics of the elements and subsystems of the system, or the system S as a whole. If there is some comparison standard, you can enter quantitative and qualitative characteristics of systems. For a quantitative characteristic, numbers are entered that express the relationship between this characteristic and the standard. Qualitative characteristics systems are found, for example, using the method of expert assessments.

The manifestation of system functions in time S(t), i.e., the functioning of the system, means the transition of the system from one state to another, i.e., movement in the state space Z.

The systems approach was used in systems engineering due to the need to study large real systems, when the insufficiency and sometimes erroneousness of making any particular decisions affected. The emergence of a systems approach was influenced by the increasing amount of initial data during development, the need to take into account complex stochastic relationships in the system and the influences of the external environment E. All this forced researchers to study a complex object not in isolation, but in interaction with the external environment, as well as in conjunction with other systems of some kind. metasystems. The systems approach allows us to solve the problem of building a complex system, taking into account all factors and possibilities, proportional to their significance, at all stages of studying the system S and building the model M.

The systems approach means that each system S is an integrated whole even when it consists of separate disconnected subsystems. Thus, the basis of the systems approach is the consideration of the system as an integrated whole, and this consideration during development begins with the main thing - the formulation of the purpose of operation.

The process of synthesis of the M model based on the systems approach is conventionally presented in Fig. b. Based on the initial data D, which is known from the analysis external system, those restrictions that are imposed on the system from above or based on the possibilities of its implementation, and based on the purpose of operation, the initial requirements are formulated T to the system model S. Based on these requirements, approximately some subsystems are formed P, elements E and the most difficult stage of synthesis is carried out - the choice IN components of the system, for which special criteria for selecting HF are used. When modeling it is necessary to ensure maximum efficiency system models.

Efficiency usually defined as a certain difference between some indicators of the value of the results obtained as a result of operating the model and the costs that were invested in its development and creation.