Text 6. Basics of Software Modelling

Modelling is simply the practice of creating a small system that has some of the same features of a larger system. When applied to software, the word modelling usually conjures up images of wall-sized UML diagrams. Internal software, however, changes so quickly that such diagrams are usually out of date by the time they are printed. Fortunately, such large-scale and unwieldy methods are not the only kind available for modelling software.

A software model does not have to start from scratch. It does not have to permeate the entire system. The only thing that a software model needs is a set of rules. The same four rules apply to all software models.

The four rules of software modelling are:

1) ownership

2) dependency

3) interface

4) identity

Unlike the rules of object-oriented design, these four apply to legacy systems as well as to new projects. Think back to the last serious

bug that you fixed. You can probably identify a violation of these rules as the cause. Briefly, ownership means that every object has exactly one owner responsible for its creation and destruction, and that ownership is not transferable. Dependency means that any bit of data used to evaluate a dependent quantity is a precedent, and that dependents must be up to date whenever referenced. Interface means that every object implements some set of interfaces, and that these interfaces allow objects to be interchanged. Identity means that all objects have unique identity, that an interface inherently identifies an object, and that all clients accessing an identical object can expect uniform behaviour.

Software modelling helps the engineer to understand the functionality of the system. Models are used for communication among stakeholders. Different models present the system from different perspectives:

• external perspective showing the system's context or environment;

• process models showing the system development process as well as activities supported by the system;

• behavioural perspective showing the behaviour of the system;

• structural perspective showing the system or data architecture.

 

Exercise 3. Give Ukrainian equivalents for the following word combinations.

conjure up images of wall-sized UML diagrams; diagrams are usually out of date by the time they are printed; large-scale and often unwieldy methods; to be not the only kind available for modelling software; to start from scratch; to permeate the entire system; to apply to all software models; ownership, dependency, interface and identity; to apply to legacy systems as well as to new projects; to think back to the last serious bug that you fixed; to identify a violation of one of these rules as the cause; responsible for creation and destruction; to be not transferable; to be up to date whenever referenced; to implement some set of interfaces; to inherently identify an object; to access an identical object; to expect uniform behaviour; communication among stakeholders; to present the system from different perspectives; to show the system's context or environment; to show the system development process as well as activities supported by the system.

 

Exercise 4. Find in the text the English for:

 

стосовно програмного забезпечення; викликати в уяві зображення величезних UML діаграм; застарілий; великомасштабні та громіздкі методи; розпочинатися з нуля; проходити через всю систему; набір правил; право власності, залежність, взаємозв’язок та ідентичність; на відміну від правил об’єктно-орієнтованого проектування; застосовуватися до успадкованих систем так само, як і до нових проектів; виправляти серйозну помилку; порушення правил; створення та знищення; право власності не передається; визначати залежну величину; бути найновішими всякий раз, коли до них звертаються; забезпечувати деяку сукупність інтерфейсів; дозволяти переставляти об’єкти; мати доступ до ідентичного об’єкту; очікувати однакової поведінки; обмін інформацією серед учасників; представляти систему з різних сторін; поведінка системи.

 

Exercise 5. Write out all verbs from the text. Identify their tense and voice.

Exercise 6. Write out all Non-Finite forms of the verb (Infinitives, Participles and Gerunds) from the text. Identify their forms and functions.

Exercise 7. Put questions to the underlined words.

1. The only thing that a software model needs is a set of rules.

2. The same four rules apply to all software models.

3. Software modeling helps the engineer to understand the functionalityof the system.

4. Models are used for communication among stakeholders.

5. Internal software changes very quickly.

6. Different models present the system from different perspectives.

7. You can probably identify a violation of these rules.

Exercise 8. Answer the questions on the text.

 

1. What is modelling?

2. What does the word modelling usually conjure up when applied to software?

3. Why are such diagrams usually out of date by the time they are printed?

4. Does a software model have to start from scratch or permeate the entire system?

5. What four rules apply to all software models?

6. What projects do these four rules apply to?

7. What can violation of these rules lead to?

8. What does ownership mean?

9. What does dependency mean?

10. What does interface mean?

11. What does identity mean?

12. What does software modelling help the engineer in?

13. What perspectives do different models present the system from?

14. What do these perspectives show?

 

Варіант 7

Exercise 1. Memorize the following words and word combinations.

Natural science - природознавство; одна з природничих наук (фізика, хімія)

engineering discipline – інженерна (технічна) дисципліна

meteorology – метеорологія

electrical engineering – електротехніка

social sciences – суспільні науки

political science – політологія

usable – придатний для використання, практичний, зручний

statіc model – статична модель

differential equation – диференційне рівняння

game theory – теорія ігор

overlap – перекривати(ся), частково збігатися

optimize – оптимізувати

hypothesis – гіпотеза

estimate – оцінювати, підраховувати

unforeseeable event – непередбачувана подія

affect – впливати

similarly – подібним чином

simulation – моделювання

equation – рівняння

relation(ship) – (взаємо)зв’язок, залежність, співвідношення

real number – дійсне число

integer number – ціле число

Boolean - булівський, булів

string – рядок

property – властивість

timing data – часові показники (характеристики)

counters – лічильні функції

event occurrence – настання події

decision variable – змінна рішення

input variable – вхідна змінна

state variable – змінна стану

exogenous variable – екзогенна (зовнішня) змінна

random variable – випадкова змінна

output variable – вихідна змінна

constant – постійна величина, константа

furthermore – до того ж, крім того, більше того

objective – ціль

constraint – обмеження

objective function – цільова функція

perspective – тут: бачення, концепція, точка зору

index of performance – показник ефективності (продуктивності)

measure – 1) показник, критерій 2) вимірювати

involved – складний, заплутаний (механізм)

 

 

Exercise 2. Read and translate the text in writing.

Text 7. Mathematical Models

A mathematical model uses mathematical language to describe a system. Mathematical models are used not only in the natural sciences and engineering disciplines (such as physics, biology, meteorology, and electrical engineering) but also in the social sciences (such as economics, psychology, sociology and political science); physicists, engineers, computer scientists, and economists use mathematical models most extensively.

Eykhoff (1974) defined a mathematical model as “a representation of the essential aspects of an existing system (or a system to be constructed) which presents knowledge of that system in usable form”.

Mathematical models can take many forms, including but not limited to dynamic systems, static models, differential equations, or game theoretic models. These and other types of models can overlap, with a given model involving a variety of abstract structures.

Often when engineers analyze a system to be controlled or optimized, they use a mathematical model. In analysis, engineers can build a descriptive model of the system as a hypothesis of how the system could work, or try to estimate how an unforeseeable event could affect the system. Similarly, in control of a system, engineers can try out different control approaches in simulations.

A mathematical model usually describes a system by a set of variables and a set of equations that establish relationships between the variables. The values of the variables can be practically anything; real or integer numbers, Boolean values or strings, for example. The variables represent some properties of the system, for example, measured system outputs often in the form of signals, timing data, counters, and event occurrence (yes/no). The actual model is the set of functions that describe the relations between the different variables.

There are six basic groups of variables: decision variables, input variables, state variables, exogenous variables, random variables, and output variables. Since there can be many variables of each type, the variables are generally represented by vectors.

Decision variables are sometimes known as independent variables. Exogenous variables are sometimes known as parameters or constants. The variables are not independent of each other as the state variables are dependent on the decision, input, random, and exogenous variables. Furthermore, the output variables are dependent on the state of the system (represented by the state variables).

Objectives and constraints of the system and its users can be represented as functions of the output variables or state variables. The objective functions will depend on the perspective of the model's user. Depending on the context, an objective function is also known as an index of performance, as it is some measure of interest to the user. Although there is no limit to the number of objective functions and constraints a model can have, using or optimizing the model becomes more involved (computationally).

 

Exercise 3. Give Ukrainian equivalents for the following word combinations.

use mathematical language to describe a system; natural sciences and engineering disciplines; use mathematical models most extensively; define a mathematical model; essential aspects of an existing system; present knowledge of that system in usable form; take many forms; dynamic systems, static models, differential equations, or game theoretic models; types of models can overlap; a variety of abstract structures; build a descriptive model of the system; an unforeseeable event; try out different control approaches in simulations; a set of variables; establish relationships between the variables; real or integer numbers, Boolean values or strings; represent some properties of the system; in the form of signals; to be represented by vectors; to be dependent on the decision; the perspective of the model's user; depending on the context;

 

Exercise 4. Find in the text 2 the English for:

науки та технічні дисципліни; природничі науки; соціологія та політологія; метеорологія та електротехніка; представлення важливих аспектів існуючої системи; приймати (мати) багато форм; включаючи, але не обмежуючись динамічними системами, статичними моделями, диференційними рівняннями або моделями теорії ігор; моделі можуть накладатися одна на одну; включати різноманітні абстрактні структури; описова модель системи; оцінювати, як непередбачувана подія може вплинути на систему; випробовувати різні концепції керування в моделюванні; описувати систему сукупністю змінних та сукупністю рівнянь; встановлювати зв’язок між змінними; дійсні або цілі числа; булеві величини або рядки; змінні рішення, вхідні змінні, змінні стану, екзогенні (зовнішні) змінні, випадкові змінні та вихідні змінні; цілі та обмеження системи; цільова функція, відома як показник ефективності.

Exercise 5. Write out all verbs from the text. Identify their tense and voice.

Exercise 6. Write out all Non-Finite forms of the verb (Infinitives, Participles and Gerunds) from the text. Identify their forms and functions.

Exercise 7. Put questions to the underlined words.

1. A mathematical model uses mathematical language to describe a system.

2. Mathematical models can take many forms.

3. Engineers can try out different control approaches in simulations.

4. There are six basic groups of variables.

5. The variables represent some properties of the system.

6. Decision variables are sometimes known as independent variables.

7. An objective function is also known as an index of performance.

 

Exercise 8. Answer the questions on the text.

1. What does a mathematical model use?

2. What are mathematical models used in?

3. What did EYKHOFF define a mathematical model as?

4. What forms can mathematical models take?

5. What do engineers use a mathematical model for?

6. What can engineers build in analysis?

7. What does a mathematical model describe a system by?

8. What do variables represent?

9. What is an actual model?

10. What groups of variables are there?

11. What can objectives and constraints be represented as?

12. What is known as an index of performance?

 

Варіант 8

Exercise 1. Memorize the following words and word combinations.

Vs – проти, відносно

quantity – величина, параметр

otherwise – в іншому випадку, інакше

linearity – лінійність

linearization – лінеаризація

assume – припускати, вважати

predictor variable – предикторна змінна, прогностичний параметр

fairly – досить, доволі

associate – пов’язувати

irreversibility – незворотність

deterministic – детермінувальний; визначальний

probabilistic (stochastic) model – ймовірнісна (стохастична) модель

state – стан

be uniquely determined – однозначно визначатися

conversely – навпаки

randomness – випадковість, ймовірність

unique value – єдине значення

probability distribution – розподіл ймовірностей

lumped parameter – зосереджений параметр

distributed parameter – розподілений параметр

homogeneous – однорідний, гомогенний

consistent – тут: однаковий, єдиний, стабільний

heterogeneous – гетерогенний, неоднорідний

 

Exercise 2. Read and translate the text in writing.