1. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 1 Software engineering for real-time systems Section 2 Dependable software

2. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 2 Objectives To: Show where, why and how software errors arise. Distinguish between correct, reliable and safe software. Establish that dependable software should be a primary design aim. Highlight the importance and influence of the software operating environment. Establish the basics of good software. Introduction

3. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 3 Qualities of dependable software

4. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 4 System behaviour under fault conditions

5. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 5 Types of software errors

6. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 6 Errors in the design process

7. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 7 A problem of syntax

8. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 8 A problem of semantics

9. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 9 Logic errors - what and when

10. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 10 Algorithmic errors

11. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 11 Poor software - the reasons

12. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 12 A flow-chart problem

13. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 13 Hierarchical modularized structure

14. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 14 Microprocessor system configurations

15. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 15 Component categorization

16. SOFTWARE ENGINEERING for REAL-TIME SYSTEMS (© J.E.Cooling 2003) Dependable software - slide 16 Review of ‘Dependable software’ You should now: Realize why, in the real world, we can never guarantee to produce fault-free systems. Know what is meant by dependable software and why it should be a primary design aim. Understand that software errors arise from problems to do with system design, software design and environmental factors. Appreciate some of the root causes of poor software.  Recognize what has to be done to produce a quality software product. END OF SECTION ‘Dependable software’