Digital Electronics PDF

## UNIT INTRODUCTION A computer system is a fundamental and permeating part of modern life. It has revolutionized the way we work, communicate, learn, and entertain ourselves. A computer system is not just a single device but a sophisticated combination of hardware and software components that work...

## UNIT INTRODUCTION A computer system is a fundamental and permeating part of modern life. It has revolutionized the way we work, communicate, learn, and entertain ourselves. A computer system is not just a single device but a sophisticated combination of hardware and software components that work together to process information, solve problems, and execute a multitude of tasks. A computer is fundamentally a digital machine because it operates based on digital data and binary logic. A computer processes data digitally by converting input information into binary code (Os and 1s), storing it in memory, and utilizing its central processing unit (CPU) to execute a series of binary-based instructions. The CPU performs arithmetic, logical, and control operations on this binary data, with the help of specialized units like the Arithmetic and Logic Unit (ALU) and control unit. Conditional branching and looping allow the computer to make decisions and repeat tasks as needed. Once processing is complete, the results are converted back to human-readable form and presented to the user through output devices. This digital approach enables computers to perform a wide range of tasks with incredible speed and accuracy. ### 1.1 Data Representation in a Digital Computer A Digital Computer is an electronic machine as it consists of millions of electronic switches. An electronic switch is very similar to an electric switch that is used to turn ON/OFF light. The main difference is that it works on very low voltage. If the electronic switch is closed, electricity flows and if it is open, electricity does not flow. Thus, switch has only two states. Binary number system used for counting also consists of two digits, 0 and 1. Therefore, binary digits, 0 and 1, are used in computer to represent the two states of a switch. When current flows in a switch, it is ON and represents binary 1. When there is no current in a switch, it is OFF and represents binary 0. A binary digit, 0 or 1 is referred to as a bit. Groups of 1s and Os are used in computer to represent data and this is known as binary code. For example, the binary code 1000100, may represent the letter D. A computer must be able to recognize codes that represent numbers, letters and special characters. These codes are known as alphanumeric codes. Alphanumeric codes include the following characters: - Lower-case letters, a to z - Upper-case letters, A to Z - Numeric digits, 0 to 9 - Special characters including punctuation marks and special symbols such as %, $, &, #, +, etc. The American Standard Code for Information Interchange (ASCII) is the most commonly used alphanumeric code. It uses 7 bits or 8-bits to represent a character and the total number of characters it represents is 128. The circuitry of a digital computer works on DC voltage. Such voltage can have only two possible values at any time. Fig. 1.1 shows a digital pulse that takes the values 0 Volt and +5 Volts. These voltage levels are assigned the binary values 0 and 1. These 0 and 1 representations are called logic 0 and logic 1, respectively. Although the logic levels in Fig. 1-1 are shown as exactly OV and +5V, in practical systems each logic level will represent a range of voltages. For example, logic 0 might be any voltage between OV and +0.8V, and logic 1 might range from +2V to +5V. The circuits that operate on these signals are called digital logic circuits. ### 1.2 Analog and Digital Signals **Analog Signals:** Analog signals are continuous signals that vary smoothly over time. These signals can take any value within a given range and are represented by a continuous waveform. Analog signals are often used in traditional audio and video transmission, as well as various physical phenomena. Analog signals shown in Fig 1.2. Examples of Analog Signals: - Analog audio signals (e.g., analog audio cassette tapes) - Analog video signals (e.g., VHS tapes) - Human speech - Analog temperature readings - Analog voltage signals **Digital Signals:** Digital signals are discrete, binary signals that represent information using a series of discrete values. These values are typically represented by Os and 1s, where 0 usually represents the absence of a signal or a low voltage, and 1 represents the presence of a signal or a high voltage. Digital signals are commonly used in modern electronic devices and communication systems. Digital signals shown in Fig 1.3. Examples of Digital Signals: - Binary code (Os and 1s) - Digital audio signals (e.g., MP3 files) - Digital images (e.g., JPEG files) - Digital video signals (e.g., MP4 files) - Digital data in computers Differences between Analog and Digital Signals: | Feature | Analog Signals | Digital Signals | |---------------------|-------------------------|-------------------------| | Representation | Continuous waveform | Discrete values (Os and 1s) | | Signal Nature | Infinite possibilities of values within a range | Limited discrete values | | Noise Susceptibility | Susceptible to noise and interference | More resistant to noise and interference | | Transmission | Degrades over long distances | Can be transmitted over long distances with less degradation | | Storage and Reproduction | Prone to quality loss during copying or storage | Can be copied and reproduced without quality loss | | Scalability | Not easily scalable | Easily scalable | | Complexity of Processing | Analog processing is often more complex | Digital processing is typically more straightforward | | Examples | Analog audio signals, analog temperature readings | Digital audio signals, digital images | ### 1.3 Digital Logic and Logic Gates Digital logic is fundamental in creating electronic devices such as calculator, computer, digital watches, etc. It is used to create digital circuits which consist of large number of logic gates. Logic gates are building blocks of digital circuits. A logic gate performs a particular logical function. Logic gate has two or more logic inputs (LOW or HIGH) and produces a single output which may be LOW (0) or HIGH (1), determined by the logic levels present at the inputs. #### 1.3.1 Logic Gates and their Truth Tables The commonly used logic gates are AND, OR, NAND, NOR, NOT, Exclusive-OR and Exclusive-NOR which are explained below. **AND Gate** AND gate operates such that the output will be at level 1 (HIGH) only when all inputs are 1 (HIGH) as shown in Fig. 1.4. The mathematical expression for the two-input AND gate is written as F=xy. For a three-input gate, it would be F=xyz, and so on for more inputs. The truth table for AND gate for two variables is shown in Fig. 1.4. | x | y | F=xy | |---|---|---| | 0 | 0 | 0 | | 0 | 1 | 0 | | 1 | 0 | 0 | | 1 | 1 | 1 | <br> **OR Gate** OR gate produces a 1 output when any input is 1 as shown in Fig. 1-5. Its mathematical expression is F=x+y, where the + stands for the OR operation and not normal addition. For a three-input OR gate, it would be F=x+y+z, and so on. The truth table for OR gate for two variables is shown in Fig. 1.5. | x | y | F=x+y | |---|---|---| | 0 | 0 | 0 | | 0 | 1 | 1 | | 1 | 0 | 1 | | 1 | 1 | 1 | <br> **NAND Gate** NAND gate combines the AND and NOT gates, such that the output will be 0 only when all the inputs are 1 as shown in Fig. 1.6. Its logic expression is F= xy which indicates that inputs x and y are first ANDed and then the result is inverted. Inversion is indicated by a bar. Thus, an AND gate always produces an output that is the inverse (opposite) of an AND gate. The truth table for NAND gate for two variables is shown in Fig. 1.6. | x | y | F=xy | |---|---|---| | 0 | 0 | 1 | | 0 | 1 | 1 | | 1 | 0 | 1 | | 1 | 1 | 0 | <br> **NOR Gate** NOR gate combines the OR and NOT gates, such that the output will be 0 when any input is 1 as shown in Fig. 1.7. Its logic expression is F=x+y, which indicates that x and y are first ORed and then the result inverted. Inversion is indicated by a bar. A NOR gate always gives an output that is the inverse of an OR gate. The truth table for NOR gate for two variables is shown in Fig. 1.7. | x | y | F=x+y | |---|---|---| | 0 | 0 | 1 | | 0 | 1 | 0 | | 1 | 0 | 0 | | 1 | 1 | 0 | <br> **NOT Gate** NOT gate is a single input gate. It converts LOW to HIGH and vice versa as shown in the truth table of Fig. 1.8. Therefore, it is commonly known as an inverter. Its logic expression is F=x. The bar in the expression indicates the inversion operation. In the output of graphical symbol, the small circle indicates inversion. The truth table for NOT gate is shown in Fig. 1.8. | x | F= x | |---|---| | 0 | 1 | | 1 | 0 | <br> **Exclusive-OR Gate** Exclusive-OR (XOR) gate has a graphic symbol similar to that of OR gate, except for the additional curved line on the input side. It produces a 1 output only when the two inputs are at different logic levels. Its output expression is F=xy+xy. The truth table for XOR gate for two variables is shown in Fig. 1.9. | x | y | F=xy+xy | |---|---|---| | 0 | 0 | 0 | | 0 | 1 | 1 | | 1 | 0 | 1 | | 1 | 1 | 0 | <br> #### 1.3.2 Truth Table A truth table represents a Boolean function or digital logic circuit in table form. It shows how a logic circuit's output or Boolean expression responds to all the possible combinations of the inputs using logic ‘1’ for true and logic ‘0’ for false. It has the following properties: - Truth table consists of rows and columns. - It shows relationship between inputs and output from a Boolean function or digital logic circuit. - It shows output for all the possible combinations of inputs using 0 for LOW and 1 for HIGH. - All the combinations of inputs are listed in columns on the left, working in the middle and output is shown in the right most column. - The input columns are constructed in the order of binary counting with a number of bits equal to the number of inputs. **Example:** Truth Table for the Boolean function is shown in Table 1.1: | X | y | Z | XZ (x.y.Z) | (x.y.z) | (x.y) | F=(x.y.Z) + (x.y.z) + (x.y) | |---|---|---|---|---|---|---| | 0 | 0 | 0 | 0 | 0 | 0 | 0 | | 0 | 0 | 1 | 0 | 0 | 0 | 0 | | 0 | 1 | 0 | 0 | 0 | 0 | 0 | | 0 | 1 | 1 | 0 | 1 | 0 | 1 | | 1 | 0 | 0 | 0 | 0 | 0 | 0 | | 1 | 0 | 1 | 0 | 0 | 0 | 0 | | 1 | 1 | 0 | 0 | 0 | 1 | 1 | | 1 | 1 | 1 | 1 | 0 | 1 | 1 | <br> #### 1.3.3 Boolean Identities Boolean identities are mathematical expressions or equations that are always true, regardless of the values of the variables involved. In the context of Boolean algebra, which deals with binary variables and logic operations (AND, OR, NOT), these identities are fundamental for simplifying and analyzing logical expressions. These Boolean identities are essential for simplifying Boolean expressions and analyzing digital circuits. Table 1.2 shows some commonly used Boolean identities. | Identity Type | Boolean Identity | |---------------------|-------------------------| | Identity Law (OR) | A+0=A | | Identity Law (AND) | A1 A | | Domination Law (OR) | A+1=1 | | Domination Law (AND) | A00 | | Complement Law (OR) | A+A=1 | | Complement Law (AND) | AA=0 | | Double Negation Law | A=A | | Idempotent Law (OR) | A+A=A | | Idempotent Law (AND) | AA=A | | Associative Law (OR) | (A+B) + C = A + (B + C) | | Associative Law (AND) | (AB) CA (BC) | | Distributive Law (AND over OR) | A. (B+C) = (AB) + (AC) | | Distributive Law (AND over OR) | A+ (BC) = (A + B). (A + C) | | Absorption Law (OR) | A+ (AB) = A | | Absorption Law (AND) | A. (A + B) = A | | Negation Law (De Morgan's Theorem) | A+B=AB | | Negation Law (De Morgan's Theorem) | AB=A+B | <br> #### 1.3.4 Boolean Function and its Conversion to Logic Circuit A Boolean function is an expression formed with binary variables, the logical operators (OR, AND and NOT), parenthesis and equal sign. A binary variable can take the value of 0 or 1. For a given value of the variables, the function can be either 0 or 1. As an example, consider the following Boolean function: **F=x+y** The function F is equal to 0, if x=0 and y=0. For all the other combinations of x and y, the function will be equal to 1. A Boolean function can be transformed from an algebraic expression into a logic circuit composed of AND, OR and NOT gates. This is explained by the following four examples. **Example 1:** Conversion of Boolean function F1=xyz to logic circuit To convert this function to logic circuit, a single AND gate is required for the term xyz. A NOT gate is also required to convert z to z, before it is input to the AND gate as shown in Fig. 1.10. **Example 2:** Conversion of Boolean function F2=x+yz to logic circuit To create the logic circuit of this function, one AND gates is required for the term yz, one NOT gate to convert y to y and an OR gate to perform OR operation on the terms x and yz. The logic circuit of this function is shown in Fig. 1.11. **Example 3:** Conversion of Boolean function F4=xy+xz to logic circuit To create the logic circuit of this function, two AND gates are required for the terms xy and xz, two NOT gates to convert x to x and y to y and an OR gate to perform the OR operation on the outputs of two AND gates as shown in Fig. 1.12. **Example 4:** Conversion of Boolean function F3=x y z + x y z + x y to logic circuit. This function has three terms. Therefore, three AND gates are required for these terms. Two NOT gates are required to obtain x and y. The output of AND gates is to be input into an OR gate to perform the OR operation between all the three terms. The logic circuit of this function is shown in Fig. 1.13. #### 1.3.5 Simplification of Boolean Function using Karnaugh Map (K-Map) **Karnaugh Map (K-Map)** Karnaugh Map (K-Map) was introduced by Maurice Karnaugh in 1953. It provides a simple method for simplifying Boolean functions. When a simplified Boolean function is converted into a logic circuit, it requires less number of gates and hence costs less. K-map is a pictorial form of a truth table. It consists of square boxes called cells. All the possible combinations of variables involved in a Boolean function are written inside the cells in their respective positions. A two-variable K-map contains 22=4 cells, three-variable 23=8 cells and so forth. **Simplification of Two-Variable Boolean Function Using K - Map** A two-variable K-map for variables A and B is shown in Fig. 1.14. It consists of four cells having two rows and two columns. Suppose the two variables are A and B. Each row and column is labelled with a variable and its complement. Complement of a variable is also called prime. Each cell contains a product term of variables A and B in its respected cell. For example, the term AB is placed in cell that is in row A and column B. Simplification of a two-variable Boolean function will be explained with the following example. **Example 1:** Simplify the Boolean function F1=AB+AB+AB using K-map. - The first step to simplify the Boolean function is to plot the terms of the function on the Karnaugh map. This function has three terms, for each term, a 1 will be placed in the corresponding cell. This is shown in Fig. 1.15. - The next step is grouping cells for simplification. Grouping means combining cells in adjacent cells. The K-map contains a pair of 1s that is horizontally adjacent and another pair of 1s that is vertically adjacent as shown in boxes in Fig. 1.16. - Combine two terms by eliminating the variable that is in both normal and complemented form. In the horizontal group, B appears in both normal and complemented form. Therefore, B will be eliminated in this group and only A is left. Similarly, in the vertical group, A appears in both normal and complemented form. Therefore, A will be eliminated in this group and only B will is left. Finally, the result is written as the sum of variables as: **F1=A+B** The following are the rules for simplifying a two-variable Boolean function. - For each term of the function, place 1 in the corresponding cell in Kanaugh map. - Make groups of two cells that contain 1. Groups may be horizontal or vertical but not diagonal. - Groups may overlap. - Eliminate the variable that is in normal and complemented form in the group. - Write the simplified function in the form of sum of variables that were not eliminated in groups. - If a K-map contains two 1s in diagonal cells then group cannot be formed which means the function cannot be simplified. **Simplification of Three-Variable Boolean Function using K - Map** A three-variable K-map for variables A, B and C is shown in Fig. 1.17. It consists of eight cells having two rows and four columns. Rows are labelled with the complement and normal form of the variable A. Each column is labelled with two variables, B and C, in their normal or complemented form. Each cell contains a product term of variables A, B and C in its respected cell. For example, the term ABC is placed in cell that is in row A and column BC. The following are the rules for simplifying a three-variable K-map. - For each term of the function, place 1 in the corresponding cell in Karnaugh map. - Form groups of four if possible otherwise groups of two. - Groups can contain only 1s. - Groups can be horizontal or vertical - Groups can overlap and wrap around the side of the K-map. - If possible include each 1 in at least one group. - Eliminate the variables that are in normal and complemented form in a group and create a term for each group. - Write the simplified function in the form of sum of terms. If a cell containing a 1 cannot be included in any group then write the full term with three variables. **Example 2:** Simplify the Boolean function **F1=ABC+ABC+ABC+ABC** - The first step to simplify the Boolean function is to plot all the terms of the function on the three variable Karnaugh map. This function has four terms, for each term, a 1 will be placed in the corresponding cell. This is shown in Fig. 1.18. - Make two horizontal groups of two 1s as shown in Fig. 1.19. - Combine two terms by eliminating the variable that is in both normal and complemented form in a group. In the group that is on the top, the variable C appears in both normal and complemented form. Therefore, C will be eliminated from this group and the combined term becomes AB. Similarly, in the bottom group also, C appears in both normal and complemented form. Therefore, C will be eliminated from this group also and the combined term becomes AB The simplified function can be written as the sum of the resulting terms after eliminating the variable C from both groups as given. F2=AB+AB **Example 3:** Simplify the following Boolean function **F3=ABC+ABC+ABC+ABC** The map for this function is shown in Fig. 1.20. There are four squares marked with 1s, one for each term of the function. Two adjacent squares are combined in the third column to give two variable term BC because A is dropped. The remaining two squares with 1s are also adjacent. The map is considered to wrap around the sides to form adjacent squares. Therefore, these two squares are combined to give two variable term AC because here B is dropped. Thus the simplified function becomes: **F3=BC+AC** **Example 4:** Simplify the following Boolean function **F4-ABC+ABC+ABC+ABC+ABC** The map to simplify this function is shown in Fig. 1.21. The function in this example has five terms, as indicated by the five squares marked with 1s. It is simplified by combining four squares in the center to give the single term C because A and B are eliminated. The remaining single square marked with a 1 is combined with an adjacent square that has already been used once. This is allowed because the combination of the two squares gives the simplified two variable term AB. The simplified function is: **F4=C+AB** **Example 5:** Simplify the Boolean function **F5=ABC+ABC+ABC+ABC+ABC** The K-map of this function is shown in Fig. 1-22. It is simplified by combining four squares in the right and left columns to give the single variable term C because A and B are eliminated. The remaining single square marked with a 1 is combined with the adjacent square on the left that has already been used once. The combination of the two squares gives the term AB. From the map we obtain the simplified function: F5=C+AB. #### 1.3.7 Principle of Duality In Boolean Algebra The Principle of Duality in Boolean algebra states that for any given Boolean expression/function, a dual expression can obtained by interchanging the AND (.) and OR (+) operators while complementing (negating) the variables. Duality in Boolean algebra refers to a fundamental property where certain operations and rules can be interchanged while still preserving the logic and truth of expressions. In other words, it highlights the symmetry between two pairs of operations: AND (conjunction) and OR (disjunction), as well as 0 (false) and 1 (true). Some examples to illustrate the Principle of Duality are shown Table 1.3. | Expression | Dual | |---|---| | 1=0 | 0=1 | | 0=1 | 1=0 | | 1.0 = 0 | 0+1=1 | | A.0 = 0 | A+1=1 | | 0.A = 0 | 1+A=1 | | A.1 = 0 | A+0=1 | | 1.A = 0 | 1+A=1 | | Α.Α = 0 | A+A=1 | | Α.Β = Β.Α | A+BB+A | | Χ.(Υ.Ζ) = (Χ.Υ).Υ | X + (Y+Z) = (X + Y) + Z | | A. (A + B) = A | A+ A.B = A | | XY + Y + ZXY = 0 | (X + Y).Υ. (Ζ + X + Y) = 1 | <br> #### 1.3.8 Uses of Logic Gates Logic gates are essential components in digital electronics and computing. They are used in numerous applications in various fields. The following are some important usages of logic gates. - **Memory Circuits:** Flip-flops and latches, which are built using logic gates, are used to store binary data in memory circuits. A flip-flop is a digital circuit that stores binary information and is widely used in digital electronics for building memory elements and sequential logic circuits. A latch is another type of digital circuit that stores binary information. Latches are often used in memory storage elements and data path circuits. - **Clock Synchronization:** Logic gates help in clock synchronization and signal processing in digital systems. - **Data Encoding and Decoding:** Logic gates are used to encode and decode data for transmission and reception in communication systems. - **Multiplication and Division:** Complex mathematical operations like multiplication and division can be performed using a combination of logic gates. - **Digital Signal Processing (DSP):** Logic gates are used in DSP circuits for filtering, modulation, and demodulation. - **Data Encryption and Decryption:** Cryptographic algorithms use logic gates for data encryption and decryption. - **Calculator Circuits:** Basic calculators use logic gates to perform arithmetic calculations. - **Traffic Light Control:** Logic gates are used in traffic light control systems to manage traffic flow. - **Robotics:** Logic gates play a crucial role in controlling the movement and decision-making of robots. - **Security Systems:** Logic gates are used in security systems to control access, alarms, and surveillance. - **Automotive Electronics:** In vehicles, logic gates are used for engine control, airbag deployment, and anti-lock brake systems (ABS). - **Home Automation:** Logic gates are employed in smart home systems to automate tasks like lighting and temperature control. - **Medical Devices:** Medical equipment uses logic gates for monitoring and controlling various functions. - **Aerospace Applications:** Logic gates are used in navigation systems, autopilots, and guidance systems for aircraft and spacecraft. ### 1.4 Software Development Life Cycle (SDLC) Software Development Life Cycle (SDLC) is the process of creating a new software or system. In other words these are the models and methodologies that experts use to develop the system. In software engineering the SDLC concept reinforces many kinds of software development techniques. These techniques process the framework for planning and controlling the creation of software. The software development life cycle (SDLC) is the process of planning, writing, modifying, and maintaining software. Developers use the methodology as they design and write modern software for computers, cloud deployment, mobile phones, video games, etc. In IT, the term "life cycle" was first used in the 1950s to describe the stages involved in developing a new computer system, but it is now commonly used to refer to all the stages in the production of any type of software. #### 1.4.1 Different Phases of SDLC The following are phases/steps in SDLC: - Defining the Problem Phase - Planning Phase - Feasibility Study Phase - Analysis Phase - Requirement Engineering Phase - Design Phase - Development/Coding Phase - Testing/Verification Phase - Deployment/Implementation Phase - Documentation Phase - Maintenance/Support Phase **1. DEFINING THE PROBLEM PHASE** In this phase the problem to be solved or system to be developed is clearly defined. All the requirements are documented and approved from the customer or the company which consists of all the product requirements to be designed and developed during the development life cycle. **Example:** Students' Examination System Development Defining the problem: A Students' Examination System is needed to be developed that covers all the aspects from Examination taking to the Students' results generations. **2. PLANNING PHASE** In the project planning phase, the project's goal is identified, and the necessary requirements for product development are assessed. A thorough evaluation of resources, including personnel and costs, is conducted, accompanied by the conceptualization of the new product. The gathered information undergoes analysis to explore potential alternative solutions. If no feasible alternatives are found, the data is organized into a comprehensive project plan, which is then presented to management for approval. **Example:** In the Students' Examination System Development project planning will be made to set the ultimate goals and an estimate of resources, such as personnel and costs, is prepared. **3. FEASIBILITY STUDY PHASE** Feasibility study is an essential aspect of project planning and decision-making in the Software Development Life Cycle (SDLC). It involves evaluating various dimensions to determine the viability and practicality of developing a proposed system. Feasibility study is the analysis and evaluation of a proposed system, to determine, whether it is technically, financially/economically, legally and operationally feasible within the estimated cost and time. Different feasibility studies are explained as follows. - **Technical Feasibility:** Technical feasibility assesses the practicality of implementing a proposed project from a technological standpoint. It involves evaluating whether the necessary technology (hardware, software), tools and resources are available or can be developed to support the system. **Example:** Consider the Students' Examination System Development project Technical Feasibility Considerations: The developing company will evaluate whether the existing infrastructure (hardware/software) can support the proposed system. - **Economic Feasibility:** Economic feasibility evaluates the financial viability of a proposed system by comparing its costs and benefits. - **Operational Feasibility:** Operational feasibility assesses the extent to which a proposed system aligns with the organization's operational processes and goals. - **Legal Feasibility:** Legal feasibility evaluates whether a proposed system complies with applicable laws, regulations, and standards. - **Schedule Feasibility:** Schedule feasibility assesses whether a system can be completed within a specified timeframe. **4. ANALYSIS PHASE** During the analysis phase the project team determines the end-user requirements. Often this is done with the assistance of client focus groups, which provide an explanation of their needs and what their expectations are for the new system and how it will perform. In this phase, the in-charge of the project team must decide whether the project should go ahead with the available resources or not. Analysis is also looking at the existing system to see what and how it is doing its job. The project team asks the following questions during the analysis. - Can the proposed software system be developed with the available resources and budget? - Will this system significantly improve the organization? - Does the existing system even need to be replaced etc? **Example:** The Students' Examination System Development project is analyzed for development. The project team will visit the College to study the existing system and will suggest the possible improvements. **5. REQUIREMENT ENGINEERING PHASE** Requirement Engineering is a crucial phase in the Software Development Life Cycle (SDLC) that focuses on gathering, analyzing, documenting, and managing requirements for the development of the proposed system. This phase lays the foundation for the subsequent stages of development and ensures that the software meets the needs and expectations of stakeholders (e.g. End users). Requirement engineering consists of the following steps. - Requirement gathering - Requirement validation - Requirements management **Requirement Gathering** Requirements gathering is a pivotal stage in the Software Development Life Cycle (SDLC), aiming to identify and document the needs and expectations of stakeholders. Various techniques are employed for this purpose, and they can be broadly classified into different types. Below are some typical types of requirement gathering types with examples. - **Interviews:** It involves direct conversations with stakeholders to gather information about their needs, expectations, and preferences. **Example:** In the Students' Examination System Development project the business analyst conducts interviews with key users and managers to understand their requirements for a new customer relationship management (CRM) system. - **Surveys and Questionnaires:** This method involves distributing surveys or questionnaires to collect information from a large number of stakeholders. **Example:** In the context of developing a Students' Examination System for a college, surveys or questionnaires could be distributed to gather information from students, faculty, and administrators. For example, the IT team might send out a survey to students and faculty members to collect feedback on the user interface and functionality of the proposed examination system. - **Observation:** This technique involves observing users in their natural work environment to understand how they currently perform tasks and identify areas for improvement. **Example:** In the context of developing a Students' Examination System for a college, the observation method involves actively watching and understanding how students, faculty, and administrators currently handle examination-related tasks in their work environments. For instance, designers could observe students during examination times, noting how they submit papers, how faculty members manage grading, and how administrators oversee the overall process. This direct observation allows the project team to identify weak areas, inefficiencies, or areas for improvement in the existing examination system. - **Document Analysis:** This approach includes reviewing existing documentation, reports, and manuals to extract relevant information about the current system or processes. **Example:** For the Students' Examination System Development project, the development team could analyze academic policies, grading criteria, and any previous reports on examination processes to extract relevant information. **Requirements Validation** Requirement validation focuses on scrutinizing the gathered requirements to ensure they align with the stakeholders' intentions. This process distinguishes itself from verification, which takes place after requirements have been accepted. During requirements validation, a thorough review is conducted to verify the completeness and accuracy of the elicited requirements. **Example:** In the context of the Students' Examination System development project, once the initial requirements for the examination system are compiled, the project team engages in requirement validation by carefully examining each specification. This ensures that the proposed features and functionalities accurately reflect the expectations of students, faculty, and administrators involved in the examination process. **Requirements Management** Requirements management is a continual process aimed at guaranteeing that the software consistently fulfills the expectations of both the acquirer and users. It involves the collection of new requirements that may emerge due to evolving expectations, changing regulations, or other sources of modification. **Example:** In the context of the Students' Examination System development project, as the Students' Examination System evolves, requirements management becomes essential. This involves actively seeking and incorporating new requirements that may arise from feedback sessions with users, changes in academic policies, or advancements in examination methodologies. Continuous requirements management ensures that the examination system adapts to the dynamic needs of the educational environment. **6. DESIGN PHASE** The design phase in the Software Development Life Cycle (SDLC) is a crucial step where the system architecture is planned and detailed specifications are created based on the requirements gathered during the analysis phase. Unified Modeling Language (UML) and various Design patterns play significant roles in this phase. Unified Modeling Language (UML) is a standardized visual modeling language widely used in software engineering and system design. It plays a crucial role in the Software Development Life Cycle (SDLC) by providing a common notation that allows developers, analysts, and stakeholders to communicate and visualize the different aspects of a system. Design patterns play a pivotal role in the SDLC by offering reusable solutions, promoting best practices, enhancing communication among team members, and contributing to the creation of maintainable and scalable software systems. They are valuable tools for software engineers striving to build high-quality, robust, and efficient software solutions. The design phase normally consists of two simple structures. These are: - Algorithms - Flow chart **1. Algorithms** Algorithms are precise and systematic procedures designed to guide the step-by-step solution of a problem. They provide a structured and detailed set of instructions for solving a particular problem or performing a specific task. **Example:** In the Students' Examination System Development project the following algorithms will find the result of a student using percentage marks. **Algorithm to find the Percentage Marks** 1. Start 2. Read Total Marks, TM 3. Read Obtained Marks, OM 4. Percentage Marks(PM) = OM/TM X 100 5. Print "Percentage Marks", PM 6. End **Algorithm to find the Student's Result** 1. Start 2. Read Percentage Marks, PM 3. If PM >=40 Then Print "Pass" Else Print "Fail" 4. End **ii. Flowcharts** A flowchart is a diagrammatic representation used to illustrate an algorithm or a process. It visually presents the sequence of steps in the algorithm through special shapes (symbols) and connects them with arrows to depict their sequence. This graphical representation offers a systematic, step-by-step solution to a