Specification Techniques

1. Specification Techniques 1

2. Overview • Introduction • What specifications can and can’t do • How and when to use specifications • Specifications in the design process • Different techniques, example • Conclusions 2

3. Introduction • specification means abstraction • different specification techniques stress different features • specifications can range from mock-up and natural language to formal methods 3

4. Benefits of specifications • identification of system properties • error and inconsistency detection • specifications can establish communication between designers and programmers • (formal) specifications can be used to create (interactive) prototypes 4

5. What specifications can’t do • guarantee a system is perfect • avoid miscommunication • 7 myths and more 5

6. When to use specifications • complex systems (e.g. multi-agent systems, multimodal systems) • trustworthy systems (e.g. e-commerce) • not for complete systems 6

7. Role of specifications in design process • use formal specification linked to empirical methods for design and evaluation • specification techniques can be used throughout the entire design process • the design process used does not matter 7

8. Empirical Design Methods & Formal methods • Empirical methods (like usability engineering or the prototyping approach) have much attention for the user’s needs. • Specification techniques add attention for the system’s behaviour in critical situations (see benefits) 8

9. Usability Engineering Assessment Specification analytical formative analysis empirical formative design implemen- tation empirical summative flow of spec/assess flow of iteration task/process 9

10. Prototyping approach requirements quick design (Pressman, 1997) prototype evaluation & refinement implementation 10

11. Which Specification Technique? • GOMS • GTA • Z • CSP • ... 11

12. Different Techniques (I) • Goals, Operators, Methods and Selection (GOMS). Hierarchical description of the user’s goals and tasks • Groupware Task Analysis (GTA). Task modeling in environments where many people interact with a system 12

13. Different Techniques (II) • Z. Mathematical description of entities and their relations. Best fitted for the description of static properties of systems • CSP. Algebraic description of interacting, dynamic processes. 13

14. Example • game to play slide puzzles • specified by using natural language and CSP-alike 14

15. Which Specification Technique • the use of the specification in the design process determines the choice of technique • use combinations (e.g. Z or CSP combined with natural language) 15

16. Accessibility of Specification Techniques • the more formal/mathematical the specification technique the steeper the learning curve: • readability. Especially specification in for example Z can scare people of. • easy to write? 16

17. Conclusions • use formal methods complementary to empirical design methods • use formal methods for critical parts, i.e. parts that: • either must function properly, • or are likely to give trouble • the right technique at the right spot 17