Electronic Communications of the EASST
Volume 57 (2013)

Proceedings of the
Second International Workshop on

Bidirectional Transformations
(BX 2013)

Preface

3 pages

Guest Editors: Perdita Stevens, James F. Terwilliger
Managing Editors: Tiziana Margaria, Julia Padberg, Gabriele Taentzer
ECEASST Home Page: http://www.easst.org/eceasst/ ISSN 1863-2122

http://www.easst.org/eceasst/


ECEASST

Preface

The Second International Workshop on Bidirectional Transformations (BX13) was held on
Sunday March 17th, 2013. It was in Rome, Italy, in conjunction with ETAPS 2013, the Euro-
pean Joint Conferences on Theory and Practice of Software. We thank the ETAPS organisers,
especially Paolo Bottoni, for their helpfulness, and the ECEASST team, especially Gabriele
Taentzer, for help on the proceedings side.

This workshop was the second in a series dedicated to bringing together researchers from four
different specialisations of computer sciences:

• Programming Languages (PL)

• Graph Transformation (GT)

• Software Engineering (SE)

• Database Systems (DB)

Each of these fields has, on at least one occasion, set out to solve a software artifact problem
that can be thought of as bidirectional. The setting for a bidirectional problem is a collection
of (concrete or virtual) artifacts, whose states must somehow be synchronised according to an
appropriate set of correctness criteria. The mechanism by which one synchronises the artifacts
is a bidirectional transformation.

For example, in the PL field, a key concept in the bidirectional field is the lens [FGM+07]. A
lens is (roughly) a pair of functions f and g between two domains S and T where f and g are in
some way inverses of one another: f describes how to populate an instance of domain T from
an instance of S, and g describes how to propagate changes to that T state back to S, taking into
account the previous state of S. Based on the domains in question, e.g. databases, strings, or tree
structures, one can construct a domain-specific language of lenses that operate on instances of
those domains; thanks to the formal properties of those lenses, the resulting language instances
can be proven to preserve data and data synchronisation. Each of the other three fields has similar
tools for dealing with similar situations.

Until recently, unfortunately, the research from these four fields existed almost in isolation.
Their terminology and jargon differ enough that communication about basic concepts like “model”
and “co-evolution” becomes difficult. Their solutions to bidirectional problems rely on different
theoretical principles based on different formal languages. Their respective corpuses of literature
rarely cite each other.

This would not matter if the bidirectional problems in each field were largely disjoint. How-
ever, there are a number of bidirectional scenarios that more than one, if not all, of the fields have
attempted to solve, with overlapping capabilities and requirements. Object-relational mapping,
for instance, is one such scenario that all four disciplines have attempted to address at least in
part.

Representatives from the four fields decided to begin meeting to see if some common ground
could be had in the form of better citation, common theory, unified research goals, or at least
more communication with and awareness of each other. The first such meeting was held in

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Preface

Tokyo in December 2008 [CFH+09], and a follow-up meeting was held at Dagstuhl in January
2011 [HSST11b, HSST11a]. A third meeting is scheduled in Banff, Canada in December 2013.
The Bx series of workshops, beginning with Bx’12 [HV12] colocated with ETAPS 2012, has
spun off from that series of meetings to provide a venue to publish work in bidirectional trans-
formations. While ongoing work on individual research projects is accepted at the workshops,
especially welcome are reports that attempt to bridge the gap between different projects, such as
benchmarks, comparison studies, and theoretical comparisons.

This year’s workshop saw nine presentations spanning the PL, GT, and SE disciplines. True to
the charter of the workshop to serve as a communication medium rather than yet another place
to publish, large portions of the workshop time were set aside for discussion. Presentation slots
were divided into three groups; in addition to the usual sets of questions asked at the end of
each presentation, at the end of each group, that group’s presenters were provided an additional
question session similar to a panel discussion. That format allowed the presenters more of an
opportunity to answer similar questions and to engage in discourse with each other.

The final segment of the workshop was held for a special kind of panel discussion called
a “fishbowl”, where the participants themselves form a panel. Five members of the audience
start the panel, but are rotated out in LIFO order as new participants come up. Participation
is encouraged because only panel members are allowed to speak. The group spent some time
brainstorming discussion topics as a whole, and then sent the action to the rotating panel.

The fishbowl panel spent most of the time discussing what the nature of benchmarking Bx
might be. Benchmarking would establish a way to set common expectations in a common lan-
guage between disciplines. It turns out that several of the participants are in the process of
forming, as part of a larger research grant (led by one of us, Stevens), a corpus of bidirectional
scenarios, and much of the discussion provided insights as to how that corpus could be built.

We were happy to receive enough submissions to give us a programme of high standard.
All papers were reviewed by at least three members of the programme committee, and there
was a careful and productive discussion process. We hope that authors of both accepted and
rejected papers will have found the reviews helpful, and are grateful to the PC members and to
the authors for their work. The versions of the papers in this volume have been revised following
the workshop.

The Bx workshop series continues next year associated with the database venue EDBT/ICDT
2014 in Athens, Greece. The Bx series of events is guided by the Bx steering committee; for
more information, see the Bx community wiki at http://bx-community.wikidot.com/.

In 2013, the programme committee was:

• Benjamin Braatz (University of Luxembourg, Luxembourg)

• Anthony Cleve (University of Namur, Belgium)

• Carlo Curino (Massachusetts Institute of Technology, USA)

• Davide Di Ruscio (University of L’Aquila, Italy)

• Zinovy Diskin (McMaster University/University of Waterloo, Canada)

• Claudia Ermel (Technische Universitt Berlin, Germany)

Proc. BX 2013 2 / 3

http://bx-community.wikidot.com/


ECEASST

• Nate Foster (Cornell University, USA)

• Ulrike Golas (Zuse-Institute Berlin, Germany)

• Frank Hermann (University of Luxembourg, Luxembourg)

• Soichiro Hidaka (National Institute of Informatics, Japan)

• Mike Johnson (Macquarie University, Australia)

• Fernando Orejas (Technical University of Catalonia, Spain)

• Jorge Perez (Universidad de Chile, Chile)

• Benjamin Pierce (University of Pennsylvania, USA)

• Dan Suciu (University of Washington, USA)

• Janis Voigtländer (University of Bonn, Germany)

and the chairs were ourselves,

Perdita Stevens (University of Edinburgh, UK) and James Terwilliger (Microsoft, USA).

Bibliography

[CFH+09] K. Czarnecki, J. N. Foster, Z. Hu, R. Lämmel, A. Schürr, J. F. Terwilliger. Bidi-
rectional Transformations: A Cross-Discipline Perspective. In Theory and Prac-
tice of Model Transformations, Second International Conference, ICMT 2009,
Zurich, Switzerland, June 29-30, 2009. Proceedings. Lecture Notes in Computer
Science 5563, pp. 260–283. Springer, 2009.

[FGM+07] J. N. Foster, M. B. Greenwald, J. T. Moore, B. C. Pierce, A. Schmitt. Combina-
tors for bidirectional tree transformations: A linguistic approach to the view-update
problem. ACM Trans. Program. Lang. Syst. 29(3), 2007.

[HSST11a] Z. Hu, A. Schürr, P. Stevens, J. Terwilliger. Bidirectional Transformation ”bx”
(Dagstuhl Seminar 11031). Dagstuhl Reports 1(1):42–67, 2011.
doi:http://dx.doi.org/10.4230/DagRep.1.1.42

[HSST11b] Z. Hu, A. Schurr, P. Stevens, J. F. Terwilliger. Dagstuhl Seminar on Bidirectional
Transformations (BX). SIGMOD Record 40(1):35–39, 2011.

[HV12] F. Hermann, J. Voigtländer (eds.). First International Workshop on Bidirectional
Transformations (BX 2012). Volume 49. ECEASST, 2012.

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http://dx.doi.org/http://dx.doi.org/10.4230/DagRep.1.1.42