Introduction to Software Engineering CEN 4010

1. Introduction to Software Engineering CEN 4010

2. Objectives of the Class • Understand how to • produce a high quality software system within time • while dealing with complexity and change • Understand System Modeling • Learn UML (Unified Modeling Language) • Use Case modeling • Object Modeling • Dynamic Modeling

3. Course outcomes • Course Outcomes: At the end of this semester you will: • Be familiar with the Software Development Life Cycle • Master the techniques to gather and specify the requirements of a medium-size software system using UML • Master the techniques to design and implement a medium-size software system • Be familiar with software testing techniques • Be familiar with system walkthroughs • Be familiar with software documentation • Be familiar with working in a small software development team

4. Software Engineering: Definition Software Engineering is a collection of techniques, methodologies and tools that help with the production of • a high quality software system • with a given budget • before a given deadline while change occurs. 20

5. Scientist vs Engineer • Computer Scientist • Proves theorems about algorithms, designs languages, defines knowledge representation schemes • Has infinite time… • Engineer • Develops a solution for an application-specific problem for a client • Uses computers & languages, tools, techniques and methods • Software Engineer • Works in multiple application domains • Has limited time • …while changes occurs in requirements and available technology

6. Software Engineering: A Problem Solving Activity • Analysis: Understand the nature of the problem and break the problem into pieces • Synthesis: Put the pieces together into a large structure For problem solving we use • Techniques (methods): • Formal procedures for producing results using some well-defined notation • Methodologies: • Collection of techniques applied across software development and unified by a philosophical approach • Tools: • Automated systems to accomplish a task

7. Factors affecting the quality of a software system • Complexity: • The system is so complex that nobody can understand the entire system • The introduction of one bug fix causes another bug • Change: • The complexity of a software system increases with each change: Each implemented change erodes the structure of the system which makes the next change even more expensive • As time goes on, the cost to implement a change will be too high, and the system will then be unable to support its intended task. This is true of all systems, independent of their application domain or technological base. • Conformity: • Must conform to arbitrary rules • Invisibility: • Software can not be seen. Only different aspects can be described

8. Why are software systems so complex? • The problem domain is difficult • The development process is very difficult to manage • Software offers extreme flexibility

9. Dealing with Complexity • Abstraction • Decomposition • Hierarchy

10. 1. Abstraction • Inherent human limitation to deal with complexity • The 7 +- 2 phenomena • Chunking: Group collection of objects • Ignore unessential details: => Models

11. Models are used to provide abstractions • System Model: • Object Model: What is the structure of the system? What are the objects and how are they related? • Functional model: What are the functions of the system? How is data flowing through the system? • Dynamic model: How does the system react to external events? How is the event flow in the system ? • Task Model: • PERT Chart: What are the dependencies between the tasks? • Schedule: How can this be done within the time limit? • Org Chart: What are the roles in the project or organization? • Issues Model: • What are the open and closed issues? What constraints were posed by the client? What resolutions were made?

12. 2. Decomposition • A technique used to master complexity (“divide and conquer”) • Functional decomposition • The system is decomposed into modules • Each module is a major processing step (function) in the application domain • Modules can be decomposed into smaller modules • Object-oriented decomposition • The system is decomposed into classes (“objects”) • Each class is a major abstraction in the application domain • Classes can be decomposed into smaller classes

13. Produce Output Transform Read Input Produce Output Transform Read Input Add R1, R10 Load R10 Functional Decomposition System Function Top Level functions Level 1 functions Level 2 functions Machine Instructions

14. Functional Decomposition • Functionality is spread all over the system • Maintainer must understand the whole system to make a single change to the system • Consequence: • Codes are hard to understand • Code that is complex and impossible to maintain • User interface is often awkward and non-intuitive

15. 3. Hierarchy • Hierarchy describes relationships between abstractions: • "Part of" hierarchy • "Is-kind-of“ (isA) hierarchy

16. CPU I/O Devices Memory Cache ALU Program Counter Part of Hierarchy Computer

17. Cell Nerve Cell Muscle Cell Blood Cell Red White Pyramidal Cortical Smooth Striate Is-Kind-of Hierarchy

18. Software Lifecycle • Software lifecycle: • Set of activities and their relationships to each other to support the development of a software system • Typical Lifecycle questions: • Which activities should I select for the software project? • What are the dependencies between activities? • How should I schedule the activities?

19. Software Process • Software Specification – requirements elicitation (func. & non-func.) and analysis. • Software Development – systems design, detailed design (OO design), implementation. • Software Validation – validating system against requirements (testing). • Software Evolution – meets changing customer needs and error correction (maintenance).

20. Software Specification Functionality of the software and constraints (non-functional requirements) on its operation must be defined. Involves: Requirements elicitation • The client and developers define the purpose of the system. • Output: a description of the system in terms of actors and uses cases. • Actors include roles such as end users and other computers the system needs.

21. Software Specification • Uses cases are general sequences of events that describe all possible actions between actors and the system for a given functionality. Analysis • Objective: produce a model of the system that is correct, complete, consistent, unambiguous, realistic, and verifiable. • Model is checked for ambiguities and inconsistencies. • Output: system model annotated with attributes, operations, and associations. Described in terms of structures and dynamic interoperation • Functional model • Object Model • Dynamic Model

22. Software Development Software to meet the specification is produced. System Design • Goals of the project are defined. • System decomposed into smaller subsystems (architectural model). • Strategies to build system identified e.g., hardware and softwareplatform, data management, control flow, and security. • Output: model describing subsystem decomposition and system strategies.

23. Software Development Object Design • Bridges the gap between analysis model and the strategies identified in the system design. Includes: • describing object and subsystem interfaces, • selecting off –the-shelf components, • Restructure object model to attain design goals e.g., extensibility, understandability, and required performance. • Output: detailed object model annotated with constraints and supporting documentation.

24. Software Development Implementation • Translation of the solution model into source code. • Implements the attributes and methods of each object integrating all objects such that they function as a single system. • Spans the gap between the detailed object design model and a complete set of source code files.

25. Software Validation Ensures the software does what the customer want, i.e., that the software conforms to its specification and meets the expectations of the customer. Validation:‘Are we building the right product?’ Ensures the software meets the expectations of the customer. Verification: ‘Are we building the product right?’ Ensures the software conforms to the specification.

26. Software Validation • Techniques • Software inspections (static): analyze and check system representations e.g., requirements documents, design diagrams, and program source code. • Software testing (dynamic): executing an implementation of the software with test data and examining the outputs against expected results. • establishes the existence of defects. • Debugging is a process that locates and corrects these defects.

27. Software Evolution Software must evolve to meet the customer needs. Software maintenance is the process of changing a system after it has been delivered. Reasons for maintenance: • to repair faults, • to adapt the software to a different operating environment, and • to add to or modify system’s functionality.

28. Implemented By Expressed in Terms Of Structured By Realized By Verified By class... class... class... ? ? class.... Application Domain Objects Solution Domain Objects Use Case Model Source Code Subsystems Test Cases ...and their models Software Lifecycle Activities Requirements Elicitation Analysis System Design Object Design Implemen- tation Testing

29. Attributes of Good Software • Maintainability • Ease of changing the software to meets the changing needs of the customer. • Dependability • Reliability, security and safety. • Efficiency • Responsiveness, processing time, and memory usage. • Usability • Appropriate user interface and adequate documentation. • Reusability • The ability to reuse components of the system in future software development projects