Expert System Interfaces
There are two interfaces to an expert system:
- The user interface
- The procedure interface
These are both important functions in the information collection
The User Interface
The user interacts with the system through a user interface which
may use menus, natural language or any other style of interaction.
The function of the expert system user interface is to present
questions and information to the operator and supply the operator's
responses to the inference engine.
In such cross referenced applications, communication between the
user interface and the inference engine is performed through the
use of a User Interface Control Block (UICB) which is passed between
- Values entered by the user must be received and interpreted
by the user interface.
- Responses can restricted to a set of possible answers, or not,
- The user interface checks all responses to insure that they
are of the correct data type.
- Any responses that are restricted to a defined set of answers
are compared against all answers.
- Whenever the user enters an illegal answer, the user interface
informs the user that his answer was invalid and prompts him to
Procedure Node Interface
The function of the procedure node interface is to receive information
from the procedures coordinator and create the appropriate procedure
call. It must be:
- Able to call a procedure and receive information from that procedure.
- Permitted to invoke any procedure allowed on its host system.
This makes the expert system useful in a much wider class of knowledge
domains than if it had no external access or only limited external
- In machine diagnostics, particularly self-diagnostic applications,
it is not possible to conclude the current state of "health"
of a machine without some information. The expert system must
be able to receive this information directly from the machine.
- Manage node functions, for example:
Able to ask specific question to obtain information from
the operator, to create an evidence node.
A leaf that is an external node indicates that data will
be used which was obtained from a procedure call.
A reference node functions to refer to another tree or subtree.
A tree may also contain intermediate or minor nodes between
the goal node and the leaf node. An intermediate node can
represent logical operations like And or Or.
The inference logic has two functions.
- It selects a tree to trace and then it traces that tree.
- Traces the tree, depth-first then left to right.
Tracing refers to the action the system takes as it traverses the
tree, asking classes [questions], calling procedures, and calculating
The selection of a tree depends on the ordering of the trees [the
order in which they appear in the rulebase]. This order can be changed
by assigning an evidence node an attribute 'initial'.
Once the values for all evidence nodes which have been assigned
an "initial" attribute have been obtained, the rules are
ordered so that the most likely to succeed is evaluated first. The
trees are constantly being updated as a selected tree is being traced
and as such can be re-ordered.
The type of information solicited by the system from the user using
questions or classes can in some systems be tailored to the level
of knowledge of the user.
In many applications, a group of prospective users are defined,
the knowledge level can be estimated, and questions presented at
a level which corresponds generally to the average user.
In other applications, knowledge of the specific domain of the
expert system might vary considerably among the group of prospective
Self Diagnostic Modes
Using an expert system in a self-diagnostic mode on a personal
computer is often done to assist the operator to diagnose the cause
of a fault or error in either the hardware or software.
Many expert systems gather knowledge from experts - but in some
cases, such as a computer, the knowledge is resident in the machine
itself, and is best sourced from there. When the accuracy of the
data supplied by an operator is potentially low, the expert system
can not effectively process it to a meaningful conclusion. In this
case, the dialog is between the machine and the diagnostic program.
The information is obtained through a process of inductive or deductive
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