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https://ceur-ws.org/Vol-3250/bxpaper1.pdf
Report on the Tenth International Workshop on
Bidirectional Transformations (BX 2022)
Xiao He1 , Li-yao Xia2 and Vadim Zaytsev3
1
University of Science and Technology Beijing, China
2
University of Edinburgh, United Kingdom
3
University of Twente, The Netherlands
Abstract
Bidirectional transformations (BX) are a mechanism for maintaining the consistency between two or more
related and heterogeneous sources of information (e.g., relational databases, software models and code, or
any other artefacts following standard or domain-specific formats). The strongest argument in favour of
BX is its ability to provide a synchronisation mechanism that is guaranteed to be correct by construction.
BX has been attracting a wide range of research areas and communities, with prominent presence at top
conferences in several different fields (namely databases, programming languages, software engineering,
graph transformation). The fast-growing complexity of software- or data-intensive systems forced
industry and academia to use and investigate different development techniques to manage many different
aspects of the systems. Researchers are actively investigating the use of bidirectional approaches to
tackle a diverse set of challenges with various applications including model-driven software development,
visualisation with direct manipulation, big data, databases, domain-specific languages, serialisers, data
transformation, integration and exchange. BX 2022 is a dedicated venue for BX in all relevant fields
and is part of a workshop series that was created in order to promote cross-disciplinary research and
awareness in the area.
1. Organisation
The BX workshop series has been running steadily since its conception in 2012 (rotating among
ETAPS, STAF, IDBT/ICDT, ∐︀Programming̃︀, PLW) until 2020 when it was postponed/cancelled
together with the rest of STAF 2020 programme due to the pandemic. It has resumed its course in
2021 in a virtual format, and this 2022 edition ran smoothly in a hybrid format, accommodating
physical participants in Nantes in France, as well as remote participants via Zoom and Webex.
Many names like Frédéric Jouault or Soichiro Hidaka, familiar to the regular BX community
but not belonging to on-site attendees, have lighted up on the screen throughout the day and
channelled their questions and comments to presenters.
We have received five submissions, and after collecting 2–3 reviews per paper, we ended up
with two accepted submissions. Then, we have solicited invited presentations from authors of
recently published BX-related papers at ICSE 2022, JSS 189 (2022) and SoSyM 20:5 (2021). The
last session of the day was decided to be spent on a plenary discussion.
BX’22: Tenth International Workshop on Bidirectional Transformations, 5 July 2022, Nantes, France
$ hexiao@ustb.edu.cn (X. He); xialiyao@seas.upenn.edu (L. Xia); vadim@grammarware.net (V. Zaytsev)
https://ustbmde.bitbucket.io/hexiao (X. He); https://poisson.chat (L. Xia); https://grammarware.net (V. Zaytsev)
0000-0003-2673-4400 (L. Xia); 0000-0001-7764-4224 (V. Zaytsev)
© 2022 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR
Workshop
Proceedings
http://ceur-ws.org
ISSN 1613-0073
CEUR Workshop Proceedings (CEUR-WS.org)
We would like to thank the programme committee members, dedicating their time and
expertise to reviewing the submissions:
◇ Jens Weber, University of Victoria
◇ Michael Johnson, Macquarie University
◇ Ravi Chugh, University of Chicago
◇ Perdita Stevens, The University of Edinburgh
◇ Fernando Orejas, Universitat Politècnica de Catalunya
◇ Leen Lambers, Brandenburgische Technische Universität Cottbus-Senftenberg
◇ Hsiang-Shang Ko, Institute of Information Science, Academia Sinica, Taiwan
◇ Kazutaka Matsuda, Tohoku University
Our appreciation also goes to all the remote participants who had to bear with the occasional
technical imperfections, and especially to physical participants who were literally there for us,
and made BX into a successful event with lively discussions and useful insights.
2. Keynote
Zhenjiang Hu is a chair professor in School of Computer Science of Peking University, and a
professor of NII by special appointment. He received his B.S. and M.S. degrees from Shanghai
Jiao Tong University in 1988 and 1991, respectively, and Ph.D. degree from University of Tokyo
in 1996. He was a lecturer (1997–2000) and an associate professor (2000–2008) at University
of Tokyo, a full professor at NII (2008-2019), and a full professor at University of Tokyo (2018-
2019), before joining Peking University in 2019. His main research interest is in programming
languages and software engineering in general, and functional programming and bidirectional
programming in particular. He is Fellow of IEEE, Fellow of JFES (Japan Federation of Engineering
Society), Member of Engineering Academy of Japan, and Member of Academy of Europe.
Dejima: A Bidirectional Collaborative Framework for Decentralized Data Manage-
ment
Data management systems are now moving from “centralised” towards “decentralised”, where
data are maintained in different sites with autonomous storage and computation capabilities. There
are two fundamental issues with such decentralized systems: local privacy and global consistency.
By local privacy, the owner of the data wish to control what information should be exposed and
how it should be used or updated by other peers. By global consistency, the systems wish to have
a globally consistent and integrated view of all data. In this talk, we shall report the progress of
our BISCUITS project [1] that attempts to systematically solve these two issues in decentralized
systems. In particular, we present a new bidirectional transformation-based approach to controlling
and sharing distributed data based on the view, describe Dejima [2], a new architectures for data
integration via bidirectional updatable views, and discuss various applications.
The keynote presentation itself covered the history of bidirectional transformations, tracing
back to its origins all the way back to VLDB 1978 [3] and POPL 2005 [4] and the seminal Shonan
report of 2008 [5]. A fundamental distinction was made between, on one side, forward-based or
get-based BX for trees [4], tables [6], strings [7], XML [8] and graphs [9], and, on the other side,
backward-based of putback-based BX [10] for trees [11], tables [12] and graphs [13]. Workshop
participants could hear some advise on how to develop dependable, correct by construction,
BX, with examples from the presenter’s own projects like BiGUL [14] and BIRDS [15], as well
as the newest of them: Dejima [2].
3. Papers
Weixin Zhang presented Decomposition Without Regret, joint work with Cristina Daivid
and Meng Wang, and used the well-known Expression Problem [16] to motivate the need
to support both object-oriented and functional decomposition. Their tool called Cook, in
memory of late William Cook, who contributed heavily to the understanding of abstraction
and decomposition [17]. The authors have also extended their talk proposal into a two-page
summary which can be found in this STAF 2022 post-proceedings.
Nils Weidmann presented Bidirectional Transformations in Practice: An Automotive Perspec-
tive on Traceability Maintenance, joint work with Anthony Anjorin and Katharina Artic. Within
the context of the automotive industry, they discuss current and potential applications of BX to
maintaining models in tandem between requirement management and architectural modelling
tools, ensuring their consistency throughout the evolution of a project. Key constraints are
identified, stemming from the high-level of abstraction of the models under study and the
regulatory nature of the industry. Three main solution strategies are investigated, as a way to
classify existing tools and to highlight possible avenues for BX applications. Their nine page
submission can also be found in this STAF 2022 post-proceedings.
4. Invited talks
Bernhard Westfechtel presented BXtendDSL: A layered framework for bidirectional model
transformations combining a declarative and an imperative language, joint work with Thomas
Buchmann and Matthias Bank. A common approach in BX is to design domain-specific languages
with a strong consistency guarantee between the two directions of a program, but such languages
generally sacrifice expressiveness, reducing their practicality. BXtendDSL follows a more
pragmatic approach. From a high-level declarative DSL, code is generated against a low-level
API, viewed as an imperative DSL. The generated code offers extension points, enabling users
to handle operational details that go beyond the scope of the high-level DSL. The resulting
language is not only expressive, but also concise and scalable. The six page submission titled
Engineering Bidirectional Model Transformations that the authors submitted for the STAF 2022
post-proceedings, can be seen as a follow-up to their JSS paper [18]
Gábor Bergmann presented Controllable and decomposable multidirectional synchronizations.
Whereas BX has traditionally focused on transformations between a source and a single view,
this work studies systems with many concurrently synchronised views, called multidirectional
synchronisations (MX). This work identifies fundamental challenges in this setting. Notably, a
"whack-a-mole" behaviour may arise, where even with individually well-behaved views, local
updates can never reach a globally consistent state. Generalisations of standard BX properties
as well as novel axioms of regularity are investigated. Remarkably, history-ignorance and very-
well-behaved-ness, which coincide for BX, generalise differently for MX. The author decided
that his original SoSyM paper [19] does not require a follow-up yet.
Xing Zhang presented Towards Bidirectional Live Programming for Incomplete Programs,
joint work with Zhenjiang Hu. Bidirectional live programming allows programmers to edit a
program by modifying its output. This work extends that idea to also allow editing of incomplete
programs. They study a core language for bidirectional live programming featuring explicit
holes. During execution, holes in the program become holes in the output. A key mechanism
is that output holes also carry the environment in which they were created, allowing one
to distinguish different instances of the same hole in the source program. This language is
implemented in a tool called Bidirectional Preview, providing a support to perform benchmarks
and to demonstrate compelling examples. The authors decided that their original ICSE paper [20]
does not require a follow-up yet.
5. Discussion panel
We would like to thank Nils Weidmann, Robbert Jongeling, Massimo Tisi, Soichiro Hidaka,
James William Pontes Miranda and Simon Dierl for their contributions to this discussion. All
three workshop chairs also participated.
Some of the major discussion points were:
◇ The Bx Examples Repository [21] at http://bx-community.wikidot.com/examples:home
◇ Forward-facing and backward-facing BX
◇ Challenges and competitions organised by other communities [22, 23, 24]
◇ Possible competition/comparison of approaches or even DSLs
◇ Impact of shared cases on replicability if the core of the problem for each case is known
and stateed
◇ Using JANI [25] https://jani-spec.org as an interchange format helped the community of
probabilistic model checking to foster tool interoperation and comparison, could we at
some point converge to such a format for BX?
◇ “Editing generated code” as one of the most common BX cases in practice
◇ Many alternative possible explorable models of synchronisation with negotiated updates
◇ Smell detection in synchronisation problems
◇ More demanding properties and stronger guarantees vs realistic properties and weaker
guarantees
◇ BX in an advisory role to suggest manual changes
◇ Maintenance of BX in an industrial context
◇ Restoring consistency with machine learning
◇ (Partial) bidirectionalisation and defining a bidirectional semantics for a language
◇ Impossibility to prove nice theoretical properties in a practical context
◇ Using known theory to study non-well-behaved systems
◇ Tolerance to imperfect/incomplete practical solutions
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