An Idea for Universal Generator of Hypotheses

Grete Lind and Rein Kuusik

Informatics, Tallinn University of Technology, Raja 15, 12618, Tallinn, Estonia

Keywords: Knowledge Discovery, Data Mining, Classification, Rule, Data Description, Universal Hypotheses

Generator.

Abstract: We know that the task of Machine Learning (ML) is defined as finding of rules for the class on the basis of

learning examples for classification of unknown object(s). But we can use rules also for describing the class

data– who/what are they? which is the task of Data Analysis and Data Mining. There are several methods

for solving this task, for example, Determination Analysis (DA) and Generator of Hypotheses (GH). In the

paper we describe an idea for Universal Generator of Hypotheses, the complex method which can solve the

tasks of DA and GH and several new ones.

1 INTRODUCTION

In the domain of machine learning (ML) many

different algorithms are in use (Mitchell, 1997), for

example ID3 (Quinlan, 1986), CN2 (Clark and

Niblett, 1987), CART (Breiman, Friedman, Olshen

and Stone, 1984) and their derivates. There are

several algorithms which try to solve the same task

on a different algorithmic and pruning techniques

bases. Some algorithms output rules

as decision trees;

some as sets of rules;

some of them find non-intersecting rules;

some find overlapping rules;

some find only one system of rules;

some algorithms find different systems of

rules;

some find a set of rules that meets certain

requirements;

etc.

This is expected, because the number of all

possible rules in case of given sets of learning

examples can be huge and each method for finding a

set of rules tries to prune the number of rules.

We present an idea of Universal Generator of

Hypotheses, which can output most of the described

possibilities of output and some new possibilities for

the researcher.

2 MACHINE LEARNING TASK

AS A DATA MINING TASK

Machine Learning task is defined as learning from

examples i.e. finding concept description (set of

rules IF X THEN Y) that is both consistent and

complete at the same time (Gams and Lavrac, 1987).

A description is complete if it covers all

examples of all classes.

A description is consistent if it does not cover

any pair of examples from different classes.

2.1 Two Directions in ML

There are two directions (subtasks) in Machine

Learning:

Direction 1 (Main task): On the basis of

learning examples to find rules for

classification of unknown object(s)

(Classification task);

Direction 2: We can use the found rules for

describing the data table (learning examples)

under analysis: “Who/what are they?” (Data

Analysis and Data Mining task).

The main steps of direction 1 are:

1) Finding set of rules;

2) Testing rules on test-examples;

3) Applying tested rules on new instances.

Here the main goal is to find the rules with a

stably good ability of recognition. There exist

several methods for solving this task.

169

Lind G. and Kuusik R..

An Idea for Universal Generator of Hypotheses.

DOI: 10.5220/0004097101690174

In Proceedings of the 14th International Conference on Enterprise Information Systems (ICEIS-2012), pages 169-174

ISBN: 978-989-8565-10-5

Copyright

c

2012 SCITEPRESS (Science and Technology Publications, Lda.)

The main steps of direction 2 are:

1) Finding set of rules;

2) Analysis of found rules;

3) Class(es) description on the basis of rules.

The main goal for direction 2 is to describe the

class -“who/what they are” on the basis of found

rules. The best representatives of the direction 2 are

methods “Determinacy Analysis” (Chesnokov,

1980; Chesnokov, 1982) and „Generator of

Hypotheses” (Kuusik and Lind, 2004). They try to

answer to the questions:

“Who are they (objects of class)?”;

“How can we describe them?”;

“What distinguishes them from the others?”.

It means that on the basis of extracted rules we

can describe the class. Use of rules makes possible

to determine what is specific for the class and what

separate different classes. Using extracted rules also

the latent structure of the class can be discovered.

It is possible that the researcher is interested in

dividing attributes into two parts: causes (C) and

effects (E) and wants to analyze relations between

them (IF C THEN E).

From the other hand it can happen that the

researcher does not know what he/she seeks. It

means that the use of corresponding methods

provides him/her with some kind of (work)

hypotheses for description and he/she must decide

whether the extracted rules can help him/her to

describe or understand the essence of the data. That

is why we call extracted rules for data description

“hypotheses”. The same situation may arise also

when the amount of extracted rules is very big and

he/she physically cannot analyze them.

Next we present a brief description of DA and GH.

2.2 Determination Analysis

The main idea behind DA is that a rule can be found

based on the frequencies of joint occurrence or non-

occurrence of events. Such rule is called a

determinacy or determination, and the mathematical

theory of such rules is called determinacy analysis

(Chesnokov, 1982).

If it is observable that an occurrence of X is

always followed by an occurrence of Y, this means

that there exists a rule “If X then Y”, or X→Y. Such

correlation between X and Y is called determination

(from X to Y). Here X is determinative

(determining) and Y is determinable.

Each rule has two characteristics: accuracy and

completeness.

Accuracy of determination X→Y shows to what

extent X determines Y. It is defined as a proportion

of occurrences of Y among the occurrences of X:

A(X→Y) = n(X Y) / n(X), where

A(X→Y) is accuracy of determination,

n(X) is a number of objects having feature X and

n(X Y) is a number of objects having both

features X and Y.

Completeness of determination X→Y shows

which part of cases having Y can be explained by

determination X→Y. It is a percentage of

occurrences of X among the occurrences of Y:

C(X→Y) = n(X Y) / n(Y), where

C(X→Y) is completeness of determination,

n(Y) is a number of objects having feature Y and

n(X Y) is a number of objects having both

features X and Y.

Both accuracy and completeness can have values

from 0 to 1. Value 1 shows maximal accuracy or

completeness, 0 means that rule is not accurate or

complete at all. Value between 0 and 1 shows

quasideterminism.

If all objects having feature X have also feature

Y then the determination is (maximally) accurate. In

case of accurate determination A(X→Y) = 1

(100%).

Majority of rules are not accurate. In case of

inaccurate rule A(X→Y) < 1.

In order to make determination more (or less)

accurate complementary factors are added into the

first part of a rule. Adding factor Z into rule X→Y

we get a rule XZ→Y.

DA enables to find different sets of rules,

depending on the order in which the attributes are

included into the analysis. One possible set of

accurate rules for well known Quinlan’s data set (of

eight persons characterized by height, hair colour

and eye colour) (Quinlan, 1984) for example

describing (persons belonging to) class ”–” is

following:

Hair.red → Class. – (C=33%);

Hair.blond & Eyes.blue → Class. – (C=67%),

The second one:

Height.tall&Hair.red → Class. – (C = 33%)

Height.short&Hair.blond&Eyes.blue → Class.

– (C=33%)

Height.tall&Hair.blond&Eyes.blue → Class. –

(C = 33%).

2.3 Generator of Hypotheses

Generator of Hypotheses (GH) is a method for data

mining which main aim is mining for patterns and

association rules (Kuusik and Lind, 2004). The goal

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is to describe the source data. Used evaluation

criteria are deterministic (not probabilistic). The

association rules it produces are represented as trees,

which are easy to comprehend and interpret.

By depth-first search (from root to leaves) GH

forms a hierarchical grouping tree. Such tree

example is given below. Method uses effective

pruning techniques.

(3) 0.667(2) 0.500(1)

Height.tall=>Hair .Dark->Eyes .Blue

0.500(1)

->Eyes .Brown

0.667(2) 0.500(1)

=>Eyes .Brown->Hair .Blond

(3) 0.667(2) 0.500(1)

Hair .Dark=>Eyes .Blue->Height.Short

0.333(1)

=>Eyes .Brown

(3) 0.667(2) 0.500(1)

Eyes .Brown=>Hair .Blond->Height.Short

The numbers above node show node’s absolute

frequency (in parentheses) and node’s relative (to

previous level) frequency (before parentheses).

Absolute frequency of node t shows how many

objects have certain attribute with certain value

(among objects having properties (i.e. certain

attributes with certain values) of all previous levels

t-1,…,1). Relative frequency is a ratio A/B, where A

is the absolute frequency of node t and B is the

absolute frequency of node t-1. For the first level the

relative frequency is not calculated.

For example we can translate the first tree

(Height.tall=>) of set of trees as “3 persons (objects/

examples) are tall, 67% of them have dark hair, and

of those (with Height.tall and Hair.dark) 50% have

blue eyes and 50% have brown eyes. Also, 67% of

tall persons have brown eyes and 50% of those have

blond hair.”

GH has the following properties:

GH guarantees immediate and simple output

of rules in the form IF=>THEN;

GH enables larger set of discrete values (not

only binary);

GH enables to use several pruning techniques;

The result is presented in form of trees;

GH enables to treat large datasets;

GH enables sampling.

3 AN IDEA FOR UNIVERSAL

GENERATOR OF

HYPOTHESES

Here we present an idea for Universal Generator of

Hypotheses (UGH), which can solve analysis task

(direction 2) and which can test hypotheses (for

example, whether some specific rule identifies some

designated class (task of query type) i.e. can the rule

open the essence of the class under description), and

generate the new ones. Building of UGH is real, due

to the existence of the base algorithm and special

techniques on the basis of which several versions of

DA (Lind and Kuusik, 2008; Kuusik and Lind,

2010; Kuusik and Lind, 2011b) and GH (Kuusik and

Lind, 2004; Kuusik, Lind and Võhandu, 2004) (both

direction 2) and IL task (direction 1) (Roosmann,

Võhandu, Kuusik, Treier and Lind, 2008; Kuusik,

Treier, Lind and Roosmann, 2009) have been

realized.

The block diagram of Universal Generator of

Hypotheses is shown in Figure 1.

Basically the variants divide into two:

1) The researcher (user) does not partition

attributes (objects’ characteristics) under

consideration – presented by blocks 3..6 on

the left side of the scheme;

2) The researcher divides attributes into cause

and effect – blocks 7..17 on the right side of

the scheme.

In the first case (blocks 3..6) simply the

enumeration of analyzable attributes is given to the

system, i.e. it is not required to observe all the

attributes that are used for describing the objects. As

a result all existing value combinations of those

attributes or relations in the form of cause-and-effect

where causes and effects are generated automatically

can be obtained. System does not determine the

causes and the effects in a relation in the same way

as the user does in case of Determinacy Analysis,

but offers different possibilities for that; the user has

to decide what is what.

Always it is possible to define the set of

observable objects (narrower than in initial data). It

is shown as a logical expression (in block 2). In a

sense of DA the narrowing of universal context

takes place. Context is the set of qualities that

describe the whole group (the ones, on the ground of

which the objects are selected). The qualities

common to the whole initial data set determine the

universal context. In the same data set it is not

possible to widen the context, it is the widest there.

AnIdeaforUniversalGeneratorofHypotheses

171

Figure 1: Block diagram of Universal Generator of Hypotheses.

Thus the context can be changed only by narrowing.

For that purpose the qualities on which basis to

make the restriction have to be shown. It is needless

to observe the attributes that determine the context

neither among causes nor among effects, since they

describe the whole subset under examination.

In the second case (blocks 7..17), blocks 14..17

describe the basic cases, where the researcher

distinguishes between cause-attributes and effect-

attributes. Block 15 presents the case, where with

each different existing combination of causes the

consequences characteristic only to it are associated.

In block 17 for each existing set of effects the causes

inducing only it are searched for. Although these

two cases are completely distinct for the user, the

difference here is only in the interpretation of the

data.

The case in block 16 differs from the one in

block 15 so that the sets of causes for which the

effects are searched for, are not restricted to the ones

that contain all the cause-attributes, but also the

combinations that contain only one or two etc

attributes from given set of attributes are observed.

In case of necessity here also the places of causes

and effects can be changed.

Blocks 8..10 represent a special case of blocks

14..15, where the user investigates what are the

effects resulting from specified cause(s). The set of

Dialogue with the user

Generation of hypotheses

In: 2

criterion for selection of

objects as a logical

expression

7

the researcher divides the

attributes into causes (C)

and effects (E)

8

In:

C as a given logical expression;

E – list of M2 attributes

11

In:

C – list of M1 attributes;

E as a given logical expression

3

the researcher does not

divide the attributes into

causes and effects

4

In:

list of M1 attributes

9

Out:

C→E, where

E – combinations by M2

10

Out:

C→E, where

E – combinations by 1,...,M2

12

Out:

C→E, where

C – combinations by 1,..,M1

13

Out:

C→E, where

C

–

combinations by M1

5

Out:

all combinations

by M1

14

In:

C – list of M1 attributes;

E – list of M2 attributes

6

Out:

all consequences in the form “cause-

effect” (C→E), where C and E are

combinations by 1,...,M1.

C and E are generated automatically

|C|+|E|=M1

16

Out:

C→E, where

C – combinations by

1,...,M1;

E – combinations by

1,...,M2

15

Out:

C→E, where

C – combinations by M1;

E – combinations by 1,...,M2

17

Out:

C→E, where

C – combinations by

1,...,M1;

E – combinations by M2

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observable objects is determined by a logical

condition over cause-attributes.

Similarly the blocks 11..13 is a special case of

blocks 14&17, where the user examines what

reasons lead to specified effect. The logical

condition of effect-attributes determines the set of

observable objects.

Again the variants in blocks 8..10 and in blocks

11..13 differ solely in the interpretation.

Basically the results findable by blocks 14..17

can be obtained by proper repeated application of

simpler variants in blocks 8..13, but it is more

practical to give that work to the computer. For the

human user giving the different value combinations

(as logical expression) one by one is arduous

enough.

Usually it is reasonable to require from the user

that the sets of causes and effects do not intersect. In

cases (of variants) 15 and 17 the overlapping

attributes are always present in the fixed-length part

(C in block 15, E in block 17) and they can also

appear in the other part of relations. In case of

variant (in block) 16 such attributes can fall into

both sides. But something that causes itself or results

from itself is not very informative.

The overlapping might make sense if more than

one value is allowed for the overlapping attribute(s)

and objects with different values of such attribute(s)

form the same cause or effect. This is possible when

causes or effects are given by a logical expression

(blocks 8 and 11 accordingly). Appearing in the

other part of relations the overlapping attributes may

provide interesting information.

The same is true for restricting the context: if

more values are allowed for the attribute(s)

determining a context then it makes sense to observe

this(these) attribute(s) in the relations.

Generator of hypotheses does not presuppose

that observable objects are classified, however it

may come in handy when solving that task.

(Automatic) classification occurs here as follows.

The user submits a list of attributes (either causes or

effects); the system finds existing value

combinations of given attributes and each such

combination describes a class of objects. Such

classification takes place in block 15 by cause-

attributes and in block 17 by effect-attributes. As

mentioned, in these cases the difference (that is so

important for the user) is only in the interpretation.

In blocks 8..13 the determination of interesting

class by the researcher takes place on the basis of a

logical condition either by causes (block 8) or by

effects (block 11).

The variants on the left side of the scheme

(blocks 3..6) where the attributes are not divided into

causes and effects by the user is realized by

Generator of Hypotheses (Kuusik and Lind, 2004).

Variants on the right side are covered by machine

learning methods. Generally the classes are given

and rules for determining them have to be found

(Roosmann et al, 2008, Kuusik et al, 2009). Usually

the ML methods assume that class is shown by one

certain attribute, but in essence it can be a

combination of several attributes shown by a logical

expression. Again, whether the given classes are

cause (blocks 8..10, 14..15) or effect (blocks 11..13,

14&17), depends on the interpretation. Determinacy

Analysis (DA) can be qualified as a subtask of

machine learning as it finds rules for one class at a

time. So it covers the variants in blocks 8..10 and

11..13. Given class can be cause (in block 8) or

effect (in block 11). Output containing combinations

by M attributes (as in blocks 9 and 13) can be found

using DA-system (DA-system, 1998), output

according to blocks 10 and 12 can be obtained using

step-wise DA methods which allow rules with

different length (Lind and Kuusik, 2008; Kuusik and

Lind, 2010). By repeated use of DA also the variants

given in blocks 14..17 can be performed.

4 CONCLUSIONS

We have presented in the paper an idea for Universal

Generator of Hypotheses. We have discussed that

matter with specialists of data analysis and they have

mentioned that the use of DA and GH is not enough,

there are several other tasks to solve and there is

need for developing some additional new

possibilities. All these possibilities are described in

the paper. Possibilities of DA and GH are also

described in the paper and they are the part of the

functionality of UGH. As we have mentioned, it is

possible to realize UGH, there exist the base

algorithm and special pruning techniques on the

basis of which the functionality of UGH is easily

realizable.

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