Preprint Article Version 3 Preserved in Portico This version is not peer-reviewed

Mind Your Outcomes: The ∆Q approach to Quality-Centric Systems Development and Its Application to a Blockchain Case-Study

Version 1 : Received: 7 December 2021 / Approved: 8 December 2021 / Online: 8 December 2021 (14:25:02 CET)
Version 2 : Received: 16 December 2021 / Approved: 21 December 2021 / Online: 21 December 2021 (13:59:45 CET)
Version 3 : Received: 21 January 2022 / Approved: 24 January 2022 / Online: 24 January 2022 (11:43:32 CET)

A peer-reviewed article of this Preprint also exists.

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. 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.

Journal reference: Computers 2022, 11, 45
DOI: 10.3390/computers11030045

Abstract

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 QSD, 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 QSD paradigm derives bounds on performance expressed as probability distributions encompassing all possible executions of the system. The QSD 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. QSD has been successfully used by 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 QSD paradigm, describes its formal underpinnings, and illustrates its use via a topical real-world example taken from the blockchain/cryptocurrency domain. QSD has enabled challenging throughput targets to be met for a globally distributed blockchain operating on the public internet.

Keywords

formal semantics; quality attenuation; distributed systems; system design; scalability; performance; feasibility; blockchain; ΔQ.

Subject

MATHEMATICS & COMPUTER SCIENCE, General & Theoretical Computer Science

Comments (1)

Comment 1
Received: 24 January 2022
Commenter: Peter Thompson
Commenter's Conflict of Interests: Author
Comment: Correction to Definition 4 and a variety of improvements to the text including:
The Introduction section has been edited and broken into subsections to improve clarity
- A new section has been added referencing recent studies on block propagation analysis
- Added missing figure captions
- A section has been added discussing limitations of the method
- A section has been added discussing practical implications for system designers
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