Software Engineering Lecture 2024/2025 PDF

Software Engineering Dr. Fatma ElSayed Computer Science Department [email protected] 2024/2025 Software Engineering – Fatma ElSayed  Questions on Lecture_01 1. Compare between the two types of softwa...

Software Engineering Dr. Fatma ElSayed Computer Science Department [email protected] 2024/2025 Software Engineering – Fatma ElSayed  Questions on Lecture_01 1. Compare between the two types of software products? 2. A software process is a sequence of activities, mention these activities? 3. Mention the key challenges that faces software engineering? 4. What are the key ethical responsibilities of software engineers? 2 2024/2025 Software Engineering – Fatma ElSayed  Course Information Contents  Introduction to Software Engineering  Software Processes  Requirements Engineering  System Modelling & Design  System Modelling & Design  System Architecture  Software Testing Strategies  Software Testing Techniques  Technical Metrics for Software 3 2024/2025 Software Engineering – Fatma ElSayed  Course Information Contents  Introduction to Software Engineering  Software Processes  Requirements Engineering  System Modelling & Design  System Modelling & Design  System Architecture  Software Testing Strategies  Software Testing Techniques  Technical Metrics for Software 4 2024/2025 Software Engineering – Fatma ElSayed  Chapter 2: Software Processes 2024/2025 Software Engineering – Fatma ElSayed  The Software Process  A software process is a set of related activities that leads to the production of a software product.  There are many different software processes but all must include four activities that are fundamental to software: 1. Software specification: The functionality of the software and constraints on its operation must be defined 2. Software design and implementation: The software to meet the specification must be produced. 3. Software validation (testing) : The software must be validated to ensure that it does what the customer wants. 4. Software evolution (maintenance) : The software must evolve to meet changing customer needs. 6 2024/2025 Software Engineering – Fatma ElSayed  Software Process Descriptions Process descriptions may also include: Order of these activities Products, which are the outcomes of a process activity. For example, the outcome of the activity of architectural design may be a model of the software architecture. Roles, which reflect the responsibilities of the people involved in the process. Examples of roles are project manager, configuration manager, programmer, etc. Pre- and post-conditions, which are statements that are true before and after a process activity has been enacted or a product produced. For example, before architectural design begins, a pre-condition could be customer approval of all requirements; a post-condition might be the review 2024/2025 of UML models describing the architecture. Software Engineering – Fatma ElSayed 7  Software Process Categories Software processes are categorized as either:  Plan-driven processes, are processes where all of the process activities are planned in advance and progress is measured against this plan.  Agile processes, which will be discussed later in details, planning is incremental and it is easier to change the process to reflect changing customer requirements.  In practice, each approach is suitable for different types of software. Generally, you need to find a balance between plan-driven and agile processes.  There are no right or wrong software processes. 8 2024/2025 Software Engineering – Fatma ElSayed  Software Process Models 1. The waterfall model Plan-driven model. Separate and distinct phases of specification and development. 2. Incremental development Specification, development and validation are interleaved. May be plan- driven or agile. 3. Reuse-Orient Software Engineering The system is assembled from existing configurable components. May be plan-driven or agile.  In practice, most large systems are developed using a process that incorporates elements from all of these models. 9 2024/2025 Software Engineering – Fatma ElSayed  The Waterfall Model 10 2024/2025 Software Engineering – Fatma ElSayed  The Waterfall Model: Advantages & Disadvantages Advantages Disadvantages  Costs of producing and approving  Simple and easy to understand and documents. implement.  No working software is produced  Easy to manage: Each phase until late stages. documents make the process visible  It takes a lot of time to produce so managers can monitor progress the final software product. against the development plan.  There is no chance to change  Phases are clearly defined and customer requirements (contract). completed one at a time.  High amount of risk. 11 2024/2025 Software Engineering – Fatma ElSayed  When to Use the Waterfall Model  The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites. In those circumstances, the plan-driven nature of the waterfall model helps coordinate the work.  The waterfall model should only be used when The requirements are very well understood from the beginning. The requirements are unlikely to change (stable) during system development. The delivery time is not a problem. 12 2024/2025 Software Engineering – Fatma ElSayed  Incremental Development Model 13 2024/2025 Software Engineering – Fatma ElSayed  Incremental Development Model  The system is developed as a series of versions (increments), with each version adding functionality to the previous version.  Incremental development is based on the idea of developing an initial implementation, exposing this to user comment and evolving it through several versions until a suitable system has been develop 14 2024/2025 Software Engineering – Fatma ElSayed  Incremental Development Benefits Incremental development has three important benefits, compared to the waterfall model: 1. The cost of accommodating changing customer requirements is reduced. The amount of analysis and documentation that has to be redone is much less than is required with the waterfall model. 2. More rapid delivery and deployment of useful software to the customer is possible, even if all of the functionality has not been included. Customers are able to use and gain value from the software earlier than is possible with a waterfall process. 15 2024/2025 Software Engineering – Fatma ElSayed  Incremental Development Benefits 3. It is easier to get customer feedback on the development work that has been done. The customer can evaluate the system at a relatively early stage in the development to see if it delivers what is required, If not, then Only the current increment has to be changed and, possibly, new functionality defined for later increments. 16 2024/2025 Software Engineering – Fatma ElSayed  Incremental Development Problems  The process is not visible. Managers need regular deliverables to measure progress. If systems are developed quickly, it is not cost-effective to produce documents that reflect every version of the system.  System structure tends to degrade as new increments are added. Unless time and money are spent on refactoring to improve the software, regular change tends to corrupt its structure. Incorporating further software changes becomes increasingly difficult and costly. 17 2024/2025 Software Engineering – Fatma ElSayed  Waterfall vs Agile [risk & Value] 18 2024/2025 Software Engineering – Fatma ElSayed  Reuse-Oriented Software Engineering  This approach is based on the existence of a significant number of reusable components.  The system development process focuses on integrating these components into a system rather than developing them from scratch.  These components are called (COTS or commercial off-the-shelf systems). 19 2024/2025 Software Engineering – Fatma ElSayed  Reuse-Oriented Software Engineering 20 2024/2025 Software Engineering – Fatma ElSayed  Types of Reusable Components There are three types of software component that may be used in a reuse-oriented process: 1. Stand-alone application systems (sometimes called COTS) that are configured for use in a particular environment. 2. Collections of objects that are developed as a package to be integrated with a component framework such as.NET or J2EE. 3. Web services that are developed according to service standards and which are available for remote invocation. 21 2024/2025 Software Engineering – Fatma ElSayed  Advantages & Disadvantages Advantages  Reduces the amount of software to be developed and so reducing cost and risks.  leads to faster delivery of the software. Disadvantages  Loss of control over evolution of reused system elements.  Requirements compromises are inevitable and this may lead to a system that does not meet the real needs of users. 22 2024/2025 Software Engineering – Fatma ElSayed  Coping with Change 2024/2025 Software Engineering – Fatma ElSayed  Coping with Change  Change is inevitable in all large software projects. Business changes lead to new and changed system requirements New technologies open up new possibilities for improving implementations Changing platforms require application changes  Change leads to rework so the costs of change include both rework (e.g. re- analyzing requirements) as well as the costs of implementing new functionality 24 2024/2025 Software Engineering – Fatma ElSayed  Reduce the Costs of Rework  There are two related approaches that may be used to reduce the costs of rework: 1. Change avoidance: 2. Change tolerance: Where the software process includes Where the process is designed so that activities that can predict possible changes can be accommodated at a changes before significant rework is relatively low cost. This normally involves required. For example, a prototype some form of incremental development. system may be developed to show Proposed changes may be implemented in some key features of the system to increments that have not yet been customers. developed. 25 2024/2025 Software Engineering – Fatma ElSayed  Coping with Changing Requirements There are two ways of coping with change and changing system requirements. 1. System prototyping: Where a version of the system or part of the system is developed quickly to check the customer’s requirements and the feasibility of some design decisions. This supports change avoidance. 2. Incremental delivery: Where system increments are delivered to the customer for comment and experimentation. This supports both change avoidance and change tolerance. 26 2024/2025 Software Engineering – Fatma ElSayed  Software Prototyping  A prototype is an initial version of a software system that is used to demonstrate concepts, try out design options, and find out more about the problem and its possible solutions.  A prototype can be used in: The requirements engineering process to help with requirements gathering and validation. Allows users to get new ideas for requirement, propose new system requirements In design processes to explore options and support user interface design process (For example, a database design may be prototyped and tested to check that it supports efficient data access for the most common user queries) 27 2024/2025 Software Engineering – Fatma ElSayed  The Process of Prototype Development 28 2024/2025 Software Engineering – Fatma ElSayed  Prototype Development  May involve leaving out functionality to reduce prototyping costs and accelerate the delivery schedule, Prototype should focus on areas of the product that are not well- understood; Error checking and recovery may not be included in the prototype; Focus on functional rather than non-functional requirements such as reliability and security 29 2024/2025 Software Engineering – Fatma ElSayed  Throw-away Prototypes  Prototypes should be discarded after development as they are not a good basis for a production system: It may be impossible to adjust the system to meet non-functional requirements; Prototypes are normally undocumented; The prototype structure is usually degraded through rapid change; The prototype probably will not meet normal organizational quality standards. 30 2024/2025 Software Engineering – Fatma ElSayed  Incremental Delivery  Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality.  User requirements are prioritised and the highest priority requirements are included in early increments.  As new increments are completed, they are integrated with existing increments so that the system functionality improves with each delivered increment 31 2024/2025 Software Engineering – Fatma ElSayed  Incremental Development and Delivery  Incremental development Develop the system in increments and evaluate each increment before proceeding to the development of the next increment by exposing it to customers for comment, without actually delivering it and deploying it in the customer’s environment. Normal approach used in agile methods;  Incremental delivery Deploy an increment for use by end-users; More realistic evaluation about practical use of software; Difficult to implement for replacement systems as increments have less functionality than the system being replaced. 32 2024/2025 Software Engineering – Fatma ElSayed  Incremental Delivery 33 2024/2025 Software Engineering – Fatma ElSayed  Incremental Delivery Advantages  Customers do not have to wait until the entire system is delivered before they can gain value from it. The first increment satisfies their most critical requirements so they can use the software immediately.  Early increments serve as prototypes, providing customers with experience that informs future system requirements, but they are part of the real system, eliminating the need for re-learning.  The priority delivery of services, followed by integration, ensures the most crucial system services undergo the most testing, reducing the likelihood of software failures.  Lower risk of overall project failure. 34 2024/2025 Software Engineering – Fatma ElSayed  Incremental Delivery Problems 1. Most systems require a set of basic facilities that are used by different parts of the system. As requirements are not defined in detail until an increment is to be implemented, it can be hard to identify common facilities that are needed by all increments. 2. The essence of iterative processes is that the specification is developed in conjunction with the software. However, this conflicts with many organizations, where the complete system specification is part of the system development contract. In the incremental approach, there is no complete system specification until the final increment is specified. This requires a new form of contract, which large customers such as government agencies may find 2024/2025 difficult to accommodate. Software Engineering – Fatma ElSayed 35  Thank You 2024/2025 Software Engineering – Fatma ElSayed