1. Trade-offs in Web development Jianyun Zhou Dept. of Computer and Information Science

2. Main goals G1: Better understanding of the software process and related technologies that concerns how to make trade-offs between the Time To Market (TTM) and reliability in web-based systems. G1: Better understanding of the software process and related technologies that concerns how to make trade-offs between the Time To Market (TTM) and reliability in web-based systems. G2: Contribute to continuous improvement of the software development process in companies where reliability and TTM need to be considered together. G2: Contribute to continuous improvement of the software development process in companies where reliability and TTM need to be considered together. G3: Dissemination and exchange of knowledge gained. G3: Dissemination and exchange of knowledge gained.

3. Trade-off between TTM and reliability Time-to-market is a main driver for Web development. It is also a main resource constraint. Time-to-market is a main driver for Web development. It is also a main resource constraint. High reliability is another driver. High reliability is another driver. Different trade-off patterns Different trade-off patterns

4. Reliability Reliability is considered as a measure of the extent to which the system can be expected to deliver usable services when these services are demanded. Reliability is considered as a measure of the extent to which the system can be expected to deliver usable services when these services are demanded. Different from correctness Different from correctness Rooms for improving reliability while leaving correctness unreachable Rooms for improving reliability while leaving correctness unreachable Robustness – techniques involve considering unpleasant facts of life at the earlier stages of the process Robustness – techniques involve considering unpleasant facts of life at the earlier stages of the process

5. Minimum development time There is a minimum development time There is a minimum development time Set a lower limit below which it is impractical to attempt to develop a system given the size of the system and the level of process productivity (for different development environment). Set a lower limit below which it is impractical to attempt to develop a system given the size of the system and the level of process productivity (for different development environment). At the minimum development time the number of defects is maximum. At the minimum development time the number of defects is maximum.

6. Trade-off patterns Ideal trade-off: improving process productivity which can only be achieved in the long run. Ideal trade-off: improving process productivity which can only be achieved in the long run. Reducing the size of a system is the only way to get some functionality in a hurry in the short run. Reducing the size of a system is the only way to get some functionality in a hurry in the short run. Effect Effect Reduce minimum development time Reduce minimum development time Reduce the number of defects Reduce the number of defects Methods Methods Cutting out frills Cutting out frills Deferring some features to later release Deferring some features to later release Reusing existing components Reusing existing components

7. Trade-off pattern (2) Extending the planned development time beyond the minimum development time reduces the number of defects. Extending the planned development time beyond the minimum development time reduces the number of defects. Effect Effect Trade time for reliability Trade time for reliability Model required for management of such trade-off Model required for management of such trade-off How much is enough? How much is enough? What is optimal distribution pattern? What is optimal distribution pattern?

8. Example Defects delivered Likelihood Very low 95.4% Low3.0% Medium1.3% High0.4% Very high 0.0% Strategy for time minimization: Strategy for extended schedule:

9. Discussion How can I get the probability distribution between variables? There two alternatives How can I get the probability distribution between variables? There two alternatives

10. Trade-off pattern (3) Identifying and fixing defects earlier can shorten development time Identifying and fixing defects earlier can shorten development time Effect Effect Not a “trade quality for time” Not a “trade quality for time” Towards the lowest defect rates also the shortest time Towards the lowest defect rates also the shortest time Model required for management of reliability risks for correctness and robustness Model required for management of reliability risks for correctness and robustness At requirement and analysis stage At requirement and analysis stage At architecture and design stage At architecture and design stage

11. Risk attributes for requirements Newness Newness Do the requirements specify something the company has never done before Do the requirements specify something the company has never done before Question: Question: Are there any state-of-art requirements? Technology, methods, languages, and hardware. (no) Are any of these new to you? (yes) Do you have sufficient knowledge in these areas? (no) Is there a plan for acquiring these knowledge? (no) Is there a plan for acquiring these knowledge? Stability Stability Are the requirements changing during the development and what are the effects on reliability and time? Are the requirements changing during the development and what are the effects on reliability and time? Completeness Completeness Are requirements missing or incompletely specified? Are requirements missing or incompletely specified?

12. Risk attributes for requirements (2) Clarity Clarity Are requirements clear and easy to understood? Are requirements clear and easy to understood? Feasibility Feasibility Are there any requirement technically difficult to implement? Are there any requirement technically difficult to implement? Validity Validity Will the requirements lead to the product the customer has in mind? Will the requirements lead to the product the customer has in mind? Questions about the determination and validation process: Prototyping, analysis, or simulation Questions about the determination and validation process: Prototyping, analysis, or simulation

13. Risk attributes for architecture and design Functionality Functionality Feasibility Feasibility Complexity Complexity Fault tolerance Fault tolerance Non-developmental elements Non-developmental elements more more

14. Discussion How to ensure the quality of the risk attributes and the questions? When to finish the planning of the questionnaire? How to ensure the quality of the risk attributes and the questions? When to finish the planning of the questionnaire?