Requirements Architecture - Agility

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1 Requirements Architecture - Agility R. Kuehl/J. Scott Hawker p. 1

2 Requirements Engineering and Agile Processes (You may be thinking) Requirements engineering model as presented is not very agile Writing a SRS, etc. sounds like a classic heavy weight process It is! But, two points to consider as good software engineers: 1. Fit the software methodology and process to the problem 2. Agile processes do equivalent requirement engineering activities still need requirements validated by stakeholders for success R. Kuehl/J. Scott Hawker p. 2

3 Requirements and Agile Traditional approach the requirements document Agile argument against tradition Communication gaps between authors and readers Change cycle is too long Challenging to capture the complete problem and system context Brain s capacity to retain information Agile answer: Continuous collaboration with stakeholders Workshops, conversation Stories (index cards) record conversations Are they the requirements? R. Kuehl/J. Scott Hawker p. 3

4 Requirements Engineering in Agile Processes Where is the Knowledge? Requirements Eng. 1. Elicitation 2. Analysis 3. Specification 4. Validation 5. Management Agile Methodology 1. Stories 2. Iteration design, customer collaboration 3. Stories, code, acceptance tests, unit tests 4. Customer collaboration, acceptance tests 5. Planning cycle, frequent iterations R. Kuehl/J. Scott Hawker p. 4

5 A Picture Worth a 1000 Words Requirements Waterfall Incremental Evolutionary Classic or agile style Design The Requirements Engineering Model Always maps Construction (coding & testing) Deployment The General Software Engineering Framework R. Kuehl/J. Scott Hawker p. 5

6 R. Kuehl/J. Scott Hawker p. 6

7 Requirements Envisioning: An Agile Best Practice Perform some high-level requirements envisioning early in the project Gain a common understanding of the scope of the problem Business goals Identify initial requirements quickly days not weeks Iteration 0 of an agile project (inception phase) Also do initial architectural envisioning Scott Ambler: R. Kuehl/J. Scott Hawker p. 7

8 Agile Requirements Envisioning Why do it? Answer basic business questions Reduce business risk everyone agrees on the problem and solution scope up front Establishes a knowledge framework to move ahead on architecture and project planning What modeling techniques? Usage use cases, scenarios Use case diagram for context Business domain model process flow, key data entities, business rules User experience story boards, prototypes R. Kuehl/J. Scott Hawker p. 8

9 When is More Upfront Detail Recommended? The domain and problem space are unknown and/or complex A commercial product (market driven requirements) Serial project milestone governance framework System engineering involving new hardware Contractual obligations Organizational culture is traditionalist R. Kuehl/J. Scott Hawker p. 9

10 Is Agility in Conflict with Architecture Design? R. Kuehl/J. Scott Hawker p. 10

11 Software Architecture and Agility Agility is not in conflict with architecture. The question is not Should I do Agile or architecture? Rather. How much architecture is done up front versus how much is deferred until project requirements are more stable? How much of the architecture should I formally document, and when? A good architecture enables agility! R. Kuehl/J. Scott Hawker p. 11

12 How Much Architecture? Two activities can add time to a project schedule: Up-front architecture design work and up-front risk identification, planning, and resolution work Rework due to fixing defects and addressing modification requests. Intuitively, these two trade off against each other. Boehm and Turner plotted these two values against each other for three hypothetical projects: One project of 10 KSLOC One project of 100 KSLOC One project of 10,000 KSLOC Balancing Agility and Discipline for the Perplexed, B. Boehm and R. Turner, Addison-Wesley, 2004 R. Kuehl/J. Scott Hawker p. 12

13 How Much Architecture? A project with a million+ lines of code is enormously complex. It is difficult to imagine how Agile principles alone can cope with this complexity if there is no architecture to guide and organize the effort. Balancing Agility and Discipline for the Perplexed, B. Boehm and R. Turner, Addison-Wesley, 2004 R. Kuehl/J. Scott Hawker p. 13

14 Agility and Architecture Evaluation and Documentation Documentation Write for the reader! If the reader doesn t need it, don t write it. But the reader may be a maintainer or other newcomer not yet on the project! Evaluation Meeting stakeholder important concerns is a fundamental agile objective Focus on meeting the most important QA scenarios Tailor a lightweight process R. Kuehl/J. Scott Hawker p. 14

Abstract Architecture Specification Document Updated to support each incremental release (i.e., a sprint Hadar, Irit, Sofia Sherman, Ethan Hadar, and John J. Harrison.

15 Abstract Architecture Specification Document Updated to support each incremental release (i.e., a sprint Hadar, Irit, Sofia Sherman, Ethan Hadar, and John J. Harrison. "Less Is More: Architecture Documentation for Agile Development." th International Workshop on Cooperative and Human Aspects of Software Engineering (CHASE) (2013) R. Kuehl/J. Scott Hawker p. 15

16 Agile Architecting Heuristics Architects and developers need to think and work Top-down design and analyze architectural structures to meet ASRs and stakeholder needs Bottom-up design solutions to accommodate implementation and environment constraints Key design decisions first, then a flow of decisions as needed Conduct experiments to analyze architecture tradeoffs ( spikes in agile terminology) E.g., SQL versus NoSQL database R. Kuehl/J. Scott Hawker p. 16

17 SAiP Authors Advice Large Systems Complex but stable requirements upfront architecture Unstable requirements candidate architecture that evolves Smaller Systems Unstable requirements get agreement on major patterns that apply Limit upfront design, evaluation, and documentation R. Kuehl/J. Scott Hawker p. 17

18 References Cockburn, Alistair, Agile Software Development, Addison-Wesley, 2002 Paetsch, Eberlein, Maurer, Requirements Engineering and Agile Software Development Kroll and Lyons, Eclipse Process Framework Presentation, Open Unified Process Distilled, 2006 Scott Ambler, odeling.htm R. Kuehl/J. Scott Hawker p. 18

Requirements Engineering and Agile Methodology

Requirements Engineering and Agile Methodology R. Kuehl/J. Scott Hawker p. 1 Requirements Engineering and Agile Processes (You may be thinking) Requirements engineering model as presented is not very agile