Software Engineering – Introduction

1. Software Engineering – Introduction DESIGN ENGINEERING Software design is an iterative process through which requirements are translated into a “blueprint” for constructing software. A design must implement all of the explicit requirements contained in the analysis model, and it must accommodate all of the implicit requirements desired by the customer. A design must be a readable, understandable guide for those who generate code and those who test and subsequently support the software. The design should provide a complete picture of the software, addressing, the data, functional, and behavioral domains from an implementation perspective.

2. Software Engineering – Introduction DESIGN ENGINEERING FURPS – Functionality, Usability, Reliability, Performance, and Supportability.

3. Software Engineering – Introduction DESIGN ENGINEERING FURPS – Functionality, Usability, Reliability, performance, and supportability. Functionality – assessed by evaluating: the feature set capabilities of the program.

4. Software Engineering – Introduction DESIGN ENGINEERING FURPS – Functionality, Usability, Reliability, Performance, and Supportability. Usability - assessed by considering: human factors, overall aesthetics, consistency, end-user documentation.

5. Software Engineering – Introduction DESIGN ENGINEERING FURPS – Functionality, Usability, Reliability, Performance, and Supportability. Reliability – is evaluated by measuring: the frequency and severity of failure, the accuracy, of output results, the mean-time-to-failure, the ability to recover from failure, the predictability of the program.

6. Software Engineering – Introduction DESIGN ENGINEERING FURPS – Functionality, Usability, Reliability, Performance, and Supportability. Performance – is measured by: processing speed, response time, resource consumption, throughput, efficiency

7. Software Engineering – Introduction DESIGN ENGINEERING FURPS – Functionality, Usability, Reliability, Performance, and Supportability. Supportability – combines: the ability to extend the program (extensibility), adaptability, serviceability testability, compatibility, configurability.

8. Software Engineering – Introduction DESIGN ENGINEERING “Abstraction is one of the fundamental ways that we as humans cope with complexity.” Grady Booch What kinds of things do we abstract?

9. Software Engineering – Introduction DESIGN ENGINEERING “Abstraction is one of the fundamental ways that we as humans cope with complexity.” Grady Booch What kinds of things do we abstract? data objects procedures modules just about anything

10. Software Engineering – Introduction DESIGN ENGINEERING “Abstraction is one of the fundamental ways that we as humans cope with complexity.” Grady Booch What kinds of things do we abstract? data objects procedures modules just about anything

11. Software Engineering – Introduction DESIGN ENGINEERING ARCHITECTURE Software architecture alludes to “the overall structure of the software and the ways in which that structure provides conceptual integrity for a system. Architecture is: the structure or organization of program components (modules), the manner in which these components interact, the structure of data that are used by the components.

12. Software Engineering – Introduction DESIGN ENGINEERING PATTERNS “A pattern is a named nugget of insight which conveys the essence of a proven solution to a recurring problem within a certain context amidst competing concerns.” “Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.” Christopher Alexander

13. Software Engineering – Introduction DESIGN ENGINEERING MODULARITY Software is divided into separately named and addressable components, sometimes called modules, that are integrated to satisfy problem requirements.

14. Software Engineering – Introduction DESIGN ENGINEERING INFORMATION HIDING Modules should be specified and designed so that information (algorithms and data) contained within a module is inaccessible to other modules that have no need for such information. This means that inadvertent errors introduced during modification are less likely to propagate to other locations within the software. Changes to the internal representation of one module should have not have an effect on other modules.

15. Software Engineering – Introduction DESIGN ENGINEERING FUNCTIONAL INDEPENDENCE Functional independence is achieved by developing modules with “single-minded” function and an “aversion” to excessive interaction with other modules. We want to design software so that each module addresses a specific subfunction of requirements and has a simple interface when viewed from other parts of the program structure. Independence is assessed by using two qualitative criteria: Cohesion – How related a module is to itself. It should perform a single task and require little interaction with the rest of the program. Coupling is an indication of the interconnectoin among modules in a software structure.

16. Software Engineering – Introduction DESIGN ENGINEERING REFINEMENT Stepwise refinement is when a program is developed by successively refining levels of procedural detail. Refinement is actually the process of elaboration. REFACTORING Refactoring is a reorganizational technique that simplifies the design )of code) of a component without changing its function or behavior.