The Mac 12/the-mac-12.iso/Shareware City/Demos/Ergo/README

Text File | 1995-03-05 | 8.0 KB | 162 lines | [TEXT/ttxt]

Ergo (TM) Documentation
Copyright (C) 1991-1995 Noetic Systems, Incorporated
All Rights Reserved


INTRODUCTION

    Ergo is a program that facilitates the creation, evaluation,
refinement, and deployment of probabilistic networks, also called belief
networks. As described in the references at the end of the tutorial stack,
a belief network is a directed acyclic graph, whose nodes are the variables
of interest, and whose edges signify associations among these variables.
The semantics of belief-network inference subsume those of most rule-based
systems, in that belief networks support Bayesian updating of probability
distributions over "if-then" rules, as opposed to deterministic rules.

    Ergo consists of a graphical drawing environment for creating a
network, a probability editor for quantifying the associations among
variables, and a probability engine for querying a belief-network
model.  The Ergo engine has been ported to run within Hypercard on the
Macintosh, and within ToolBook for Microsoft Windows.
Versions of the engine are also available as C libraries for the
Macintosh, MS-DOS, Microsoft Windows, and Unix operating systems.
Thus, belief-network models developed in Ergo can be embedded within a
wide variety of programs to provide the intelligence required for
classification, diagnosis, and constraint-satisfaction problems.

SYSTEM REQUIREMENTS

    Ergo requires a math coprocessor, and thus runs on a Macintosh II,
SE/30, or later. A hard disk is strongly recommended, although two disk
drives will do in a pinch. Ergo requires System 6.0 or higher, and is
compatible with System 7.


INSTALLING ERGO

    Make sure the original disk is read-only, make a backup copy of the
disk, and place the original disk in a safe place before proceeding.

    If you have a hard disk, copy Ergo into your Applications folder (if
you don't have a folder called Applications, create one) and place the
Networks folder in the same folder as your other documents.
Alternatively, you can create one folder called Ergo, and copy the program
and the Networks folder into it.

    If you have two floppy disk drives, place Ergo and the Networks
folder on the same disk, and your system software on the other disk.


USING ERGO

    The following is a cursory explanation of how to use the program; for
more details, see the Ergo Tutorial Hypercard stack and the user's manual.

    To use Ergo, simply launch the program by double-clicking on its icon,
or by selecting the icon and then selecting the Open command from the File
menu. Ergo has the usual Macintosh commands; from the File menu, select the
New command to create a new, blank network window; select the Open command
to open a previously saved network, such as the examples in the Networks
folder; select the Close command to close a network window, and (if it's
not a demonstration version) select the Save or Save As... command to save
any changes you make to a network.

    The network window has three icons in its palette: the selection tool,
the node tool, and the edge tool. You choose the current tool, which is
highlighted, by clicking on its icon or by pressing the Tab key. The
selection tool allows you to select nodes or edges and drag them, and to
change the names of a node. Click on the network window with the node tool
to create a node. To use the edge tool, click on a node, drag the cursor to
another node, and release the mouse button. You can also copy, paste, cut,
and delete groups of nodes and their associated edges by selecting them and
using the appropriate command from the Edit menu. You can also paste
networks into drawing programs, since they are also copied to the clipboard
as PICTs.

    After you've created nodes and defined the associations among
them, you must quantify the strengths of those associations by opening
the probability editor. You can open this window by double-clicking on
any one of the nodes, or by choosing the Probabilities... command from
the Window menu. Choose the node to define by using the slider in the
upper-left corner, or on its associated left-right arrow buttons.
Enter the number of values that that node can assume (2-99) by
clicking on the field under the node's name. A list of labels for each
value is below the number of values; click on any label to change it
from its default (LblXXX) to something meaningful (e.g., High, Medium,
Low for a three-valued node).

    On the right half of the probability editor, there is a
spreadsheet-like interface. For each value of the node, and for each
possible combination of its parents' values, you must enter the
probability that the node will assume a particular value given that
particular combination of its parents' values. For example, if a node
named X has edges pointing towards it coming from two parents named A
and B, and if X can assume the values (Yes, No, Maybe) and each of its
parents can assume the values (True, False), you must specify 12
probabilities. If X had no parents, the name "Priors" would appear as
the heading for the probability cells; otherwise, the name of the
first parent (in this case, A) would appear as the heading. Note that,
since the possible values for X are listed vertically, each column in
the matrix must sum to 1, since these are exhaustive and mutually
exclusive possiblities. To scroll through all possible combinations of
the parents' values, use the vertical slider in the upper-right corner
of this window.

    After a network has been created and quantified, you can compile the
model and query it by selecting the Compile command from the Graph menu.
Note that you cannot change the names of nodes, delete nodes or edges, or
copy or paste nodes while in compiled mode; to return to Editing mode,
select the Edit command from the Graph menu.  When you select the Compile
command, Ergo's probability engine will initialize the probability
distributions over each node in the network, and display each node as a
histogram corresponding to the probability distribution over its values. To
query the network model, first set the value of the node of interest by
command-clicking on that node and choosing one of its values from the
pop-up menu. Ergo will compute posterior-probability distributions for all
of the variables in the network given the evidence that you have just
entered. To observe these distributions, which are presented as histograms,
option-click on any node. You can enter additional evidence by
command-clicking on other nodes, or you can retract all evidence by
selecting the Initialize command from the Graph menu.

    By observing the results of entering evidence, you can change your
model (adding or deleting nodes or edges, or changing some of the
probabilities for a particular node) so that its behavior conforms more
closely to that of an expert.


USE AND DISTRIBUTION

    Ergo, its manual, the tutorial stack and this document are
copyrighted material. You may freely distribute this document and any
demonstration copies of Ergo (including example networks and example
stacks and the tutorial stack), provided that you include this document
with any distribution, and that you do not change the contents of any of
these files in any way. Demonstration copies of Ergo do not save networks,
and are indicated as demonstration copies in the box shown when
launching Ergo, as well as in the About... box.

    You may not distribute, in any form or under any circumstances, a
licensed or non-demonstration version of Ergo, or the manual, or its
associated files, except as expressly provided in a signed license agreement
between you and Noetic Systems, Incorporated.


FURTHER INFORMATION

    If you have any comments or questions about Ergo, this document, the
tutorial stack, the demonstration program, or any of the other files distributed,
we'd like to hear from you. You can contact Noetic Systems, Incorporated via
any of the following media:

Electronic Mail (Internet) : [e-mail]
Telephone        :      410.889.4079
Facsimile        :      410.889.4183
US Postal Service:  Noetic Systems, Incorporated
                              2054 Maryland Avenue
                              Baltimore, Maryland 21218-4545