This research report describes MEXSES, a rule-based expert system
for environmental impact assessment at a screening level, implemented
for the analysis of water resources development projects in the Lower
The system was developed and implemented under contract to the Mekong
Secretariat, Bangkok, Thailand.
The system provides an example of a qualitative and logic-based
technique for the analysis of complex environmental assessment problems.
Rather than attempting to predict, in any absolute sense,
environmental impacts and to evaluate them,
we have organized the available information in a consistent and
plausible framework that links project characteristics and environmental
features to expected impacts in a simple logical format
of IF ... THEN rules.
This assessment is based on mainly qualitative descriptions of the
relevant variables and descriptors of development projects and the
environment. It uses logic and rules derived from expert opinions,
rather than algorithms and numerical models,
to arrive at conclusions, and thereby an assessment of expected
MEXSES represents an experimental approach to the analysis of
complex systems. Recognizing that the uncertainties are tremendous,
our main objective is to construct a plausible and consistent framework
for thinking about the problem, a tool to organize and analyze the
information in a specific institutional and planning-oriented context.
Rather than numerical precision of questionable origin, we seek to
identify basic patterns and trends and approximate classifications,
and to challenge our own mental models
(or any numerical ones for that matter), in a dialogue with the computer.
The expert system is primarily an attempt to model our understanding,
our perception of the problem, rather than ``reality''.
It is also designed as a collection and repository of expertise and
relevant information, compiled from more than one expert and numerous
other sources of information, in a format that can directly, and in
fact automatically, be brought to bear on the difficult
task of environmental impact assessment.
So as to organize the relevant information, MEXSES provides specific
for development projects such as dams and reservoirs, hydropower and
irrigation projects, or fisheries, aquaculture and navigation development.
The checklists are based on the Environmental Guidelines Series of
the Asian Development Bank.
The system uses hierarchical checklists, organized by problem classes,
following the logic of project planning and implementation
and a qualitative assessment procedure based on rules and descriptors,
which allow the analyst to assess the individual subproblems identified
in the checklists in terms of their expected environmental impacts.
On the basis of this list of estimated impacts, a summary assessment of a
given project can be performed
in terms of a few aggregated criteria covering environmental
as well as socio-economic aspects of river basin development.
The knowledge representation uses a simple syntax for rules and decision
tables, that operate on descriptors of project features, environmental
characteristics and impacts. The descriptor definitions are implemented
in a frame-like, object-oriented language that includes the descriptor name,
the list of symbols and associated
numerical ranges for allowable descriptor values (most descriptors can
have both numerical or symbolic values concurrently),
references to rules that can be used to
derive a descriptor value from other descriptors, instructions for an
ask function to obtain the value from the user interactively,
and the linkage to a hypertext system of help and
information, definitions of concepts and a glossary of terms.
The inference engine uses look-ahead pre-processing for the dynamic
pruning of the inference tree. It offers both forward and backward chaining
functions for standard assessment and an alternative hypothesis testing feature,
Different modes of interaction, all based on a fully menu-driven graphical
user interface implemented in X Windows, offer alternative levels of
verbosity with the optional display, and selection by the user, of rules,
as well as an integrated hypertext system of help and
explanatory text functions.
In addition to the expert system proper, the software system includes a
project data base as well as an integrated geographical information
system (GIS) for the management of spatial environmental data.
The report makes a brief review of environmental impact assessment
methods and tools. It discusses expert systems technology,
with emphasis on environmental applications.
The Lower Mekong Basin and its specific environmental
problems, as well as the Mekong Secretariat's environmental policy are
Subsequently, the software system is described from a user's perspective,
followed by a detailed description of the methodology employed and
In the final chapter, a number of issues around the successful
application of such a system are discussed, including a number of
suggested improvements and extensions to the current operational