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Article

Mind Your Outcomes: The ΔQSD Paradigm for Quality-Centric Systems Development and Its Application to a Blockchain Case Study †

1
Formal Methods Group, IOG, 4 Battery Road, 25-01 Bank of China Building, Singapore 049908, Singapore
2
Department of Informatics, University of Bergen, 5020 Bergen, Norway
3
Predictable Network Solutions Ltd. (PNSol), Stonehouse GL10 2PG, UK
4
Institute of Information and Communication Technologies, Electronics, and Applied Mathematics, Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
*
Authors to whom correspondence should be addressed.
This paper is an extended version of our paper published in 33rd Symposium on Implementation and Application of Functional Languages (IFL21), held online 1–3 September 2021.
Academic Editor: Paolo Bellavista
Computers 2022, 11(3), 45; https://doi.org/10.3390/computers11030045
Received: 16 December 2021 / Revised: 24 February 2022 / Accepted: 25 February 2022 / Published: 17 March 2022
(This article belongs to the Special Issue Blockchain-Based Systems)
This paper directly addresses a long-standing issue that affects the development of many complex distributed software systems: how to establish quickly, cheaply, and reliably whether they can deliver their intended performance before expending significant time, effort, and money on detailed design and implementation. We describe ΔQSD, a novel metrics-based and quality-centric paradigm that uses formalised outcome diagrams to explore the performance consequences of design decisions, as a performance blueprint of the system. The distinctive feature of outcome diagrams is that they capture the essential observational properties of the system, independent of the details of system structure and behaviour. The ΔQSD paradigm derives bounds on performance expressed as probability distributions encompassing all possible executions of the system. The ΔQSD paradigm is both effective and generic: it allows values from various sources to be combined in a rigorous way so that approximate results can be obtained quickly and subsequently refined. ΔQSD has been successfully used by a small team in Predictable Network Solutions for consultancy on large-scale applications in a number of industries, including telecommunications, avionics, and space and defence, resulting in cumulative savings worth billions of US dollars. The paper outlines the ΔQSD paradigm, describes its formal underpinnings, and illustrates its use via a topical real-world example taken from the blockchain/cryptocurrency domain. ΔQSD has supported the development of an industry-leading proof-of-stake blockchain implementation that reliably and consistently delivers blocks of up to 80 kB every 20 s on average across a globally distributed network of collaborating block-producing nodes operating on the public internet. View Full-Text
Keywords: formal semantics; quality attenuation; distributed systems; system design; scalability; performance; feasibility; design space exploration; blockchain; proof of stake; ΔQ formal semantics; quality attenuation; distributed systems; system design; scalability; performance; feasibility; design space exploration; blockchain; proof of stake; ΔQ
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MDPI and ACS Style

Haeri, S.H.; Thompson, P.; Davies, N.; Van Roy, P.; Hammond, K.; Chapman, J. Mind Your Outcomes: The ΔQSD Paradigm for Quality-Centric Systems Development and Its Application to a Blockchain Case Study. Computers 2022, 11, 45. https://doi.org/10.3390/computers11030045

AMA Style

Haeri SH, Thompson P, Davies N, Van Roy P, Hammond K, Chapman J. Mind Your Outcomes: The ΔQSD Paradigm for Quality-Centric Systems Development and Its Application to a Blockchain Case Study. Computers. 2022; 11(3):45. https://doi.org/10.3390/computers11030045

Chicago/Turabian Style

Haeri, Seyed H., Peter Thompson, Neil Davies, Peter Van Roy, Kevin Hammond, and James Chapman. 2022. "Mind Your Outcomes: The ΔQSD Paradigm for Quality-Centric Systems Development and Its Application to a Blockchain Case Study" Computers 11, no. 3: 45. https://doi.org/10.3390/computers11030045

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