Finding Incremental Solutions for Evolving Requirements

Finding Incremental Solutions for Evolving Requirements Neil Ernst, Alexander Borgida, Ivan Juretanernst@cs.ubc.ca -‐ borgida@cs.rutgers.edu -‐ ijureta@fundp.ac.be 1

The problem • Changing requirements are costly and a major source of software errors. • Requirements drift from implementation. • Lack of tool support for requirements evolution. • If we dont know what, or more importantly, why we are doing something, "how" we do it is inconsequential. 2

The solution • Focus on the case of evolving requirements due to unanticipated change. • Introduce a simple propositional formalism on a case study. • Define solutions to requirements problems. • Define the requirements evolution problem. • Use a functional interface to determine what changes to make and why. • Evaluate the performance of solution-‐finding.3

Requirements problems: Goals, tasks, and assumptions • Requirements describe stakeholder desires for the new system (e.g., “protect cardholder data”). • These desired states we call goals. • Goals are iteratively reﬁned until operationalized by an implementation task. • A goal model deﬁnes a space of alternative designs for satisfying goals, constrained by domain assumptions. The requirements problem: given a set of goals, which tasks and assumptions satisfy those goals?1 [1] [1] P. Zave and M. Jackson, “Four Dark Corners of Requirements Engineering,” TOSEM, vol. 6, pp. 1-30, 1997.4

PCI Data Security Standard (PCI-DSS) 1. Build and Maintain a Secure Network 2. Protect Cardholder Data 3. Maintain a Vulnerability Management Program 4. Implement Strong Access Control Measures 5. Regularly Monitor and Test Networks 6. Maintain an Information Security Policy5

PCI-DSS model Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per server No money for new servers Virtualize Use multiple server servers instances6

PCI-DSS model Increase Goal revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per server No money for new servers Virtualize Use multiple server servers instances6

PCI-DSS model Increase revenues Accept payment Avoid financial losses and penalties Accept cash Accept credit card Reﬁnement Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per server No money for new servers Virtualize Use multiple server servers instances6

PCI-DSS model Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per server Task No money for new servers Virtualize Use multiple server servers instances6

PCI-DSS model Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Domain Buy strongbox Implement only one primary function per assumption server No money for new servers Virtualize Use multiple server servers instances6

PCI-DSS model Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per Alternatives server No money for new servers Virtualize Use multiple server servers instances6

PCI-DSS model Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per server No money for new servers Virtualize Use multiple server instances servers Conﬂict6

Formalizing the requirements problem • D, S ⊢ G1 • A ﬂavour of the Techne RE language. Concepts • Goals G • Domain assumptions D • Sets of implementation tasks S Relations • implication (Horn clause) • conﬂict (A, B, A ⋀ B →⊥) [1] Jureta, Borgida, Ernst, Mylopoulos, “Techne: Towards a New Generation of Requirements Modeling Languages with Goals,7 Preferences, and Inconsistency Handling.” RE2010, 115-124.

The REKB • Store requirements problem elements as logical sentences. • i.e., goals, tasks, domain assumptions and relations • Deﬁne a TELL/ASK interface for solving requirements problems. • TELL: atoms, sentences. • UNTELL: asserted atoms. • ASK: solutions to requirements problem in REKB.8

Standard ASK questions 1. Are goals achieved from G tasks? (linear time complexity) 2. Find minimal sets of tasks G1 G2 that achieve goals (NP-‐hard complexity) T1 T2 T39

Standard ASK questions X 1. Are goals achieved from G tasks? (linear time complexity) 2. Find minimal sets of tasks G1 G2 that achieve goals (NP-‐hard complexity) T1 T2 T39

Standard ASK questions 1. Are goals achieved from G tasks? (linear time complexity) 2. Find minimal sets of tasks G1 G2 that achieve goals (NP-‐hard complexity) T1 T2 T39

Standard ASK questions 1. Are goals achieved from G tasks? (linear time complexity) 2. Find minimal sets of tasks G1 G2 that achieve goals (NP-‐hard complexity) T1 T2 T3 Smin = {T1, T3} {T2, T3}9

Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per server No money for new servers Virtualize Use multiple server servers instances10

The requirements evolution problem • Given an existing solution Si which satisfies D, Si ⊢ G, and • modified entities (δ(G), δ(D), δ(S)); • Find Ŝ so that δ(D), Ŝ ⊢ δ(G), such that this satisfies some desired property π, relating Ŝ to Si.11

Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per server No money for new servers Virtualize Use multiple server servers instances12

Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per server No money for new serversSi Virtualize Use multiple server servers instances12

Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per Use Secure Hash server on CC # No money for new serversSi Virtualize Use multiple server servers instances12

Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per Use Secure Hash server on CC # No money for new serversSi Virtualize Use multiple server servers instances New Requirement12

Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per Use Secure Hash server on CC # No money for new servers Virtualize Use multiple server servers instances New Requirement12

Increase revenues Accept payment Avoid financial losses and penalties Accept credit Accept cash card Use Verifone Use Moneris Be PCI POS POS compliant Buy strongbox Implement only one primary function per Use Secure Hash server on CC # No money for new servers Virtualize Use multiple server serversŜ instances New Requirement12

Useful properties π 1. Minimal implementation eﬀort. 2. Minimal change eﬀort solutions. 3. Maximal familiarity solutions. 4. Solution reuse in family of solutions. Si Sa Sb Sc a b c a c a b c f g h d e d f d g13

Implementing the REKB • REKB is a functional description. • Leverages an Assumption-‐based Truth Maintenance System1 (ATMS). • Incremental, minimal, conﬂict-‐tolerant. • Other options: SAT solvers, SMT, PsB. • Problem solver tracks implemented tasks, versions elements, retracts atoms. [1] J. de Kleer, “An assumption-based TMS,” Artiﬁcial Intelligence, 28, 1986, pp. 127-162.14

Evaluating the REKB 100• Evaluate the REKB 10 Time (s) approach on 1 • the PCI-‐DSS • random requirements 0.1 models 0.01 0 50 100 150 200 250 300 350 400 450 500 550 600 # Nodes15

Evaluating the REKB (2) • Test 1 incremental New%task performance Time (s) on three High%level evolution 0.1 Conﬂict scenarios (400 nodes) Naive add Incremental add16

Conclusions • The REKB is a framework for managing goals, tasks, and domain assumptions. • Find incremental solutions, and ﬁnd optimal solutions.FIX • Solving requirements problems provide the “why” for maintenance activity.17

Thanks! http://neilernst.net @neilernst github.com/neilernst18

Finding Incremental Solutions for Evolving Requirements

by Neil Ernst on Sep 09, 2011

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Finding Incremental Solutions for Evolving Requirements — Presentation Transcript