  Bigraphs are an emerging modeling formalism for structures in ubiquitous
computing. Besides an algebraic notation, which can be adopted to provide an
algebraic syntax for bigraphs, the bigraphical theory introduces a visual
concrete syntax which is intuitive and unambiguous at the same time; the
standard visual notation can be customized and thus tailored to domain-specific
requirements. However, in contrast to modeling standards based on the
Meta-Object Facility (MOF) and domain-specific languages typically used in
model-driven engineering (MDE), the bigraphical theory lacks a precise
definition of an abstract syntax for bigraphical modeling languages. As a
consequence, available modeling and analysis tools use proprietary formats for
representing bigraphs internally and persistently, which hampers the exchange
of models across tool boundaries. Moreover, tools can be hardly integrated with
standard MDE technologies in order to build sophisticated tool chains and
modeling environments, as required for systematic engineering of large systems
or fostering experimental work to evaluate the bigraphical theory in real-world
applications. To overcome this situation, we propose an abstract syntax for
bigraphs which is compliant to the Essential MOF (EMOF) standard defined by the
Object Management Group (OMG). We use typed graphs as a formal underpinning of
EMOF-based models and present a canonical mapping which maps bigraphs to typed
graphs in a natural way. We also discuss application-specific variation points
in the graph-based representation of bigraphs. Following standard techniques
from software product line engineering, we present a framework to customize the
graph-based representation to support a variety of application scenarios.
