Rulebase technology for GIS applications
Object creation using a rulebase
Many things about AM/FM/GIS or facilities objects can be easily codified in terms of
relations and validations. These are generally the category of real-world characteristics
called object properties. A relation can be described as the way in which the object fits
into the overall data model for all facilities and land. Every database has an inherent data
model, a description of what data is to be stored for each object, and how the objects
relate to each other. Data models for AM/FM/GIS are particularly important, since they
have both spatial and aspatial characteristics. For example, a valve object must have data
about its operating type, size and material, and the direction that it is turned to operate. It
may also have to have a record in a table or file for each time it is exercised or operated.
These are examples of aspatial relationships that can be codified for an object using
relations.
Validations are another form of spatial or aspatial object properties that are used to
represent valid characteristics of the object, rather than relationships. A simple, almost
universal example is the unique identifier, such as a valve that must have a unique
company identifier assigned to it. More complex validations are also common, such as
the value of a property for an object that is dependent on a value of another property.
Pipe coating is a good example of this type of validation. A pipe object may have a set of
valid values for its material property, including plastic and steel. The same object may
also have a property for coating type, which would have various valid values for steel,
but no valid values for plastic. Thus, the validity of the pipe-coating-type property is
contingent on the selection of the pipe material. This type of complex validation is
sometimes referred to as con~ingent validity. Validations are often checked through a
post-process in AM/FM/GIS, using a Quality Control (QC) application to ensure validity.
Of course, there is more to the real-world nature of facilities than their relations and
validation properties. Facilities objects also have behavior; things that they do or things
that can be done to them, which are generally known in object speak as methods. For an
AM/FM/GIS object, most methods have to do with how they fit into a network model,
and how they appear on a map (either on screen or hardcopy.) These
connectivity/cartography methods can also easily be described as a set of rules that match
business practices. As an example, when a valve object is placed into the model and
map, its rules may dictate that it should attach itself to a pipe, and rotate its symbol
according to the line angle or orientation of the pipe to which it is attached.
Creating a RuleBase through Requirements Analysis and Data Modeling
The clarification and documentation of these three types of characteristics for objects
representing real-world facilities in the AM/F M/GIS is the function of requirements
analysis and data modeling. Here, then, is one key advantage of using a RuleBase
technique: data modelers can describe the properties (relations and validations) for
objects using standard manual processes or CASE tools. These standard techniques are
well known and highly productive. The results of these modeling efforts are usually
embodied in structured relational tables. From there, it is the job of an engine or codegenerator
to construct this part of the object, with tools that are available on the
commercial market to minimize hands-on coding.
While standard relational techniques may be used for describing relations and validations,
connectivity/cartography is typically better described using an object modeling technique.
A variety of tools and techniques are available to support this approach, and they are well
documented in the literature of the industry. Among the most popular tools is the
Universal Modeling Language (UML), for which there are several compatible CASE
tools. The key to successful object modeling is to recognize the patterns in business
behavior, and to organize them in the most effective way according to function and value.
These techniques are invaluable aids in the consistent description of the business rules
that govern the behavior of the facilities objects.
But a word of caution: experience has shown that O-O modeling techniques can take on a
life of their own, supplanting business knowledge and common sense with technical zeal.
It is the wise object modeler who regularly reviews the business purposes for each
element in the model, and tests the value of religious rigor and purity of technique against
the business needs of constructing the model with reasonable speed and accuracy.
