pdf: 600KB - Potsdam Institute for Climate Impact Research

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integrated simulations. ... MODCOM provides a series of pre-built components implementing
these interfaces that manage many aspects of simulations – high-level simulation services,
numerical integration of differential equations, data management, data analysis, and visual
representation of simulation components and outputs. MODCOM is language neutral, and is built
on top of Microsoft’s COM specification; any language that supports COM can take advantage of
MODCOM’s modeling services. ... The central concept of MODCOM is that a simulation model
is best constructed as a collection of simulation objects (SimObjs) that are organized and
managed by a simulation environment (SimEnv) that provide a range of high-level services
common to most simulations. MODCOM provides a general-purpose simulation framework by
which this can occur. By creating models as well-defined components, the opportunities for
reusing the components in other simulations are greatly increased. Similarly, by handling general
simulation services in a generic manner, the modeller is relieved of having to provide these
services in each simulation; he/she simply takes advantage of the services offered by the
framework, and can concentrate instead on defining the details of the component of interest."
There are several things to note about MODCOM. The first is that it is a rare example of the
development of a modelling framework by groups from different institutions collaborating
together on an equal footing, and with the primary purpose of developing the framework. Other
initiatives are usually led by one particular group, operating within the context of a specific
modelling project. The second is that the emphasis given to the component (module): the aim is
to enable multiple components to be glued together to make a model, rather than to support the
development of the components themselves. Third, MODCOM is based on a programming
approach: in its current form, you need to be a programmer to make a module, and you need to be
a programmer to make a model out of several components. There is an intention to develop
visual modelling environments for both tasks, but that is in the future.
A1.3 IMA: Integrating Modelling Architecture
The IMA is a very ambitious project aimed at developing a generic framework capable of
bringing together a wide variety of modelling paradigms in a single model (Villa, 2001). The
paradigms include not only conventional simulation models based on differential/difference
equations, but also agent-based models, cellular automata, optimisations models, statistical
models, and so on. It is motivated by the recognition that a given problem - say, one involving
land use planning with complex environmental and sociological aspects, requires a variety of
approaches for its solution.
IMA is heavily predicated on a declarative modelling approach. The primary role for this is to
define the characteristics of the interface that individual modules present to the rest of the system.
In order to allow modules to talk to each other, to the model manager, and to tools for input,
output and analysis, they have metadata attached to them defining their characteristics with
respect to time, space and behaviour. The time aspect relates to the when a module is called
during the simulation time cycle. Space relates to attributes such as grid/polygon/point
representation, spatial granularity and spatial extent. Behaviour defines the type of modelling
paradigm for that module: System Dynamics, event-based, or whatever. These characteristics are
defined in XML, and are independent of the actual implementation of the module, which can
either be programmed or represented declaratively.
The IMA vision is a sweeping one. It does share quite a lot in common with standard
component-based approaches (modules, a simulation object hierarchy, as simulation controller,
etc), though is distinguished by its total commitment to a declarative, ontologically-rich language
for characterising modules in general, and XML in particular. At the time of writing, IMT (the
Integrating Modelling Toolkit - the implemented prototype of IMA) is still under development,
and it remains to be seen how realisable the vision is in practice.