COMPSCI 705 & SOFTENG 702. API Design. Jamie Diprose

Transcription

1 COMPSCI 705 & SOFTENG 702 API Design Jamie Diprose

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3 Learning objectives Explain what an API is, why they are used and quality attributes. Explain how user-centred design can be used to design APIs. Explain how the Cognitive Dimensions can be used to design APIs. Explain evidence based design guidelines for designing APIs.

4 What is an API? Collection of code with an interface that enables other developers to use it Synonyms: dev kits, frameworks, libraries, toolkits.

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6 Why use an API? Saves time (code reuse) Hides implementation details Provides functionality that is hard to implement Provides standard experience for users

7 API Stakeholders API Designers API Users Product Users

8 API Quality Attributes Usability Power Learnability Efficiency Memorability Errors Satisfaction Expressiveness Extensibility Evolvability Performance & robustness

9 Designing a Usable API 1. User-centred design 2. Cognitive Dimensions 3. Evidence based design guidelines

10 User-Centred Design Needs of users & tasks they perform first Iterative process Evaluation tightly linked Often includes: stakeholder interviews, scenarios, personas, user studies and the Cognitive Dimensions.

11 User-Centred Design Example Carnegie Mellon Natural Programming project Has used user-centred design to design APIs with SAP. Stakeholder interviews User requirements gathering User evaluations

12 Cognitive Dimensions Vocabulary to help designers weigh up design decisions affecting usability. Diffuseness/terseness: how many symbols are required to express a meaning? Abstraction level: what are the minimum and maximum levels of abstraction exposed? Hidden dependencies: are dependencies between entities visible or hidden?

13 Cognitive Dimensions Example 1 robot = Robot() person = Person() robot.say_to( <gesture type= wave > Hello human </ gesture>, person) robot.say_to( <wave> Hello human </wave>, person)

14 Cognitive Dimensions Example 2 robot = Robot() person = Person() robot.say_to( <wave> Hello human </wave>, person) length = robot.say_duration( Hello human ) robot.gaze_and_wait(person.head) robot.say( Hello human ) robot.gesture_and_wait(gesture.wave, duration=length)

15 Cognitive Dimensions Example 3 Visual Studio Usability Group. Perform lab studies. Participants perform programming tasks. The Cognitive Dimensions is used to analyse the data.

16 Evidence based design guidelines Constructor design Method placement Documentation design Environment

17 Evidence based design guidelines Constructor design Method placement Documentation design Environment

18 Evidence based design guidelines Constructor design Document intent Method placement Documentation design Code examples show best practices Match scenarios to API elements Environment Document factors affecting penetrability Format and presentation

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22 Evidence based design guidelines Constructor design Method placement Documentation design Environment

23 Evidence based design guidelines Constructor design Method placement Documentation design Environment

24 References Stylos, J., & Myers, B. (2007, September). Mapping the space of API design decisions. In Visual Languages and Human- Centric Computing, VL/HCC IEEE Symposium on (pp ). IEEE. Stylos, J., Graf, B., Busse, D. K., Ziegler, C., Ehret, R., & Karstens, J. (2008, September). A case study of API redesign for improved usability. In Visual Languages and Human-Centric Computing, VL/HCC IEEE Symposium on (pp ). IEEE. Clarke, S. (2004). Measuring API usability. Doctor Dobbs Journal, 29(5), S1-S5. Stylos, J., & Clarke, S. (2007, May). Usability implications of requiring parameters in objects' constructors. In Proceedings of the 29th international conference on Software Engineering (pp ). IEEE Computer Society. Stylos, J., & Myers, B. A. (2008, November). The implications of method placement on API learnability. In Proceedings of the 16th ACM SIGSOFT International Symposium on Foundations of software engineering (pp ). ACM. Robillard, M. P., & Deline, R. (2011). A field study of API learning obstacles. Empirical Software Engineering, 16(6), Kleinschmager, S., Hanenberg, S., Robbes, R., Tanter, É., & Stefik, A. (2012, June). Do static type systems improve the maintainability of software systems? An empirical study. In Program Comprehension (ICPC), 2012 IEEE 20th International Conference on (pp ). IEEE. Endrikat, S., Hanenberg, S., Robbes, R., & Stefik, A. (2014, May). How do API documentation and static typing affect API usability?. In Proceedings of the 36th International Conference on Software Engineering (pp ). ACM.