Zusammenfassung
Summary Software Engineering principles
- Kurs
- IGIS01_E (IGIS01_E)
- Hochschule
- IU Internationale Hochschule ( )
It contains all topics covered in the software engineering principles exam.
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UNIT 1 – STRUCTURE AND ORGANIZATION OF INFORMATION SYSTEMSWHAT I NEED TO KNOW
- explain what it means to encode information using binary code
- name the units that make up a Von Neumann computer
- identify the typical elements in distributed systems
- name the elements of communication networks
- understand the types of enterprise information systems
1.1 0 AND 1 AS THE BASIS OF ALL IT SYSTEMS
Digital systems store and process information in binary form, which means in the form of sequences of 0 and 1.
One bit corresponds to the amount of information in an answer to a question with only two possibilities, but of
course there can be more than two possible answers to a question, so we need bit sequences to store amounts
of information that are greater than one bit.
examples of real word applications of binary form:
- light switch that turns on and off
- flashlight that turns on and off
- optical storage media, like CDs, DVDs and Blu-Ray discs that have a spiral track made up of small peaks
and valleys. Every change (increase or decrease) means 1 and every non-change means 0
- magnetic storage media such as hard drives, they store data on disks and are divided into many small
areas: these areas can be set to one of two possible magnetic states, one state is spoken as “one” and
the other as “zero”.
All data stored and all programs executed on a computer system, manifest themselves as sequences of 0 and 1.
BOOLEAN OPERATIONS
The foundation of processing sequences of 0 and 1 were laid in the 19th century by George Boole. The term
Boolean algebra describes an algebraic structure with the two elements (0 and 1) and the logical operations
(AND, NOT, OR). The functionality of these operations can be implemented easily with electrotechnical
assemblies and combined to form complex circuits.
Boolean operation AND:
- two-digit operation;
- two boolean values (X and Y)
- if both values are equal to 1 then their value is 1;
- if one of them is not equal to 1, then their value is 0;
Boolean operation OR:
- two-digit operation;
- two boolean values (X and Y);
- if at least one of the values is equal to 1 then their value is 1;
- if both of them are not equal to 1 then their value is 0;
Boolean operation NOT:
- has only one input digit;
- it negates the value X to the other
- the value 1 is evaluated as 0, and 0 as 1;
1
,STORING NUMBERS AND LETTERS
Computer systems can also calculate ordinary numbers and store and display letters and other characters.
There are defined mappings and standards for this (for ex. ASCII or UTF-8).
To perform mathematical calculations, the numbers are first converted into the binary system in which they get
calculated and then transferred back to the decimal system. The conversion is necessary because computer
systems can only calculate with 0 and 1.
1.2 VON NEUMANN ARCHITECTURE
The basic functionality of all current computer systems was introduced in 1945 by John Von Neumann. He
developed the idea of storing the computer programs in a shared memory (the main memory) of the computer,
together with the data being processed.This made re-programming computers possible, because the
instructions for processing data could be easily changed. Almost every common computer system produced
today follows the Von Neumann Architecture.
2
,It comprises 5 units:
• memory;
• control unit;
• input/output;
• the arithmetic logical unit (ALU);
• a bus system connecting the units.
Most of the components are integrated into a central processing unit (CPU).
memory - it is used to store binary coded data and programs; there is only one type of memory and it is divided
into small areas that are numbered with a unique address (data stored in a memory cell, can be called up via
their address).
control unit - it’s the coordinator of the CPU. It is responsible for first loading the commands of a program to be
executed from the memory into the CPU in the correct order and interpreting them. Then, the source and
destination of the data to be processed must be interconnected with the ALU. Finally the calculator must be
informed as to which calculation it should carry out with the data.
arithmetical logical unit (ALU) - it is part of the CPU and it does the calculations. It has a number of executable
and logical functions. the available set of commands of the ALU is mapped to simple binary operations that can
be carried out very quickly (ex. AND, OR, NOT).
input/output units - they are the interface between the system and its surrounding environment. They are
responsible for the flow of incoming and outgoing data and programs: it includes communication with the user
and communication with other systems via system interfaces.
bus system - it’s a data transmission system used by all units for communication. The transmission capacity and
the speed of the bus significantly determine the speed of the computer. Modern bus systems work more like a
point-to-point network than a bus system.
The Von Neumann Architecture was not designed to solve a specific problem, but to solve all calculable
problems, because the internal structure of the computer doesn’t determine how the data are processed, and
since the program are in a changeable memory, the instructions for how the data are processed can be adapted
without having to exchange hardware components of the computer system.
This invention made programming software possible.
HOW THE VON NEUMANN COMPUTER WORKS
The program commands are stored in successive memory cells within the memory. When a program is started,
the control unit causes the first command to be loaded into the ALU. A command contains instructions for:
• loading data from the memory to the ALU;
• carrying out calculations on data already loaded into the ALU;
• storing data.
After the command has been loaded into the calculator, it is executed. The cycle is repeated with the next
instructions.
*each command is executed within one step of the CPU clock; today the time spent adding two values within
the ALU is less than 1 nanosecond.
1.3 DISTRIBUTED SYSTEMS AND COMMUNICATION NETWORKS
A distributed software system is a software that can only be used in conjunction with several computers
connected via a communication network.
One important evolution is the switch from single mainframes to distributed software systems, which
communicate autonomously using a global network infrastructure. Their underlying hardware and software
components are located on computers that are connected by a communication network and communicate by
exchanging messages via that network.
3
, TYPICAL ELEMENTS IN DISTRIBUTED SYSTEMS
A distributed system consists of a server, a client, a communication network and an agreement on the structure
of the messages to be sent.
server - they are computers that make functions (also called services) accessible to other computers via a
communication network.
example:
• search engine servers enable information to be found on the internet
• weather service servers provide information on the current weather situation
• online retailers servers offer search functions in the inventory
client - they are the computers that use the services offered by the servers.
example - a network printer is a server that offers the printing services for the local network, every computer
that prints out a document via this printer is a client.
Both roles only relate to the offering and requesting of services, and not to the required hardware of the
devices.
Most systems within an enterprise network act as a server as well as a client, depending on the service
considered.
Example - the customer relationship manager(CRM) system acts as a server, providing customer address data to
the enterprise resource planning (ERP) system which then becomes the client. On the other hand the ERP also
acts as a server to the CRM system, providing daily turnovers of every customer.
communication network - it connects clients and servers and it consists of:
• physical components for data transmission (wires, antennas)
• technical components for routing and transferring data (routers, switches..)
• network interfaces to connect a device to a communication network (ethernet interface card,
bluetooth chip)
network interface - it enables a computer to communicate with other computers. In addition to physical
connection (cable socket, built-in radio chip), it requires support from the operating system (software).
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