Ontologies, Conceptualizations,and Possible Worlds

Revisiting “Formal Ontologies and Information Systems”10 years later

Nicola Guarino

CNR Institute for Cognitive Sciences and Technologies,

Laboratory for Applied Ontology, Trento, Italy

www.loa-cnr.it

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Summary

• Reality, perception, and conceptualizations• Computational ontologies as logical characterizations of

conceptualizations• Differences betwen ontologies; kinds of ontology

change

• Evolution with respect to previous works of mine:• What are possible worlds? What is the domain of discourse?• Clearer distinction between possible worlds and logical models• Explicit role of perception in clarifying the notion of “conceptualization”• hPossible worlds as sensory states (also in a metaphorical sense:

perception as observation perspective focusing on “raw data”)• More detailed account of kinds of ontology change

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Ontology and Ontologies

• Ontology: the philosophical discipline

• Study of what there is (being qua being...)...a liberal reinterpretation for computer science:

content qua content, independently of the way it is represented

• Study of the nature and structure of “reality”

• ontologies:

Specific (theoretical or computational) artifactsexpressing the intended meaning of a vocabulary

in terms of primitive categories and relations describingthe nature and structure of a domain of discourse

Gruber: “Explicit and formal specifications of a conceptualization”

...in order to account for the competent use of vocabulary in real situations!

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What is a conceptualization

• Formal structure of (a piece of) reality as perceived and organized by an agent, independently of:• the vocabulary used • the actual occurence of a specific situation

• Different situations involving same objects, described by different vocabularies, may share the same conceptualization.

apple

melasame conceptualization

LI

LE

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Example 1: the concept of red

{a}

{b}

{a,b}

{}

a b

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Example 2: the concept of on

ba

{<a,b >}

ab

{<b,a >}

ab {}

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Relations vs. Conceptual Relations

conceptual relations are defined on a domain space <D, W>

rn 2Dn

n : W 2Dn

(Montague's intensional logic)

ordinary relations are defined on a domain D:

But what are possible worlds?What are the elements of a domain of discourse?

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What is a conceptualization? A cognitive approach

• Humans isolate relevant invariances from physical reality (quality distributions) on the basis of:

• Perception (as resulting from evolution)• Cognition and cultural experience (driven by actual needs)• (Language)

• presentation: atomic event corresponding to the perception of an external phenomenon occurring in a certain region of space (the presentation space).

• Presentation pattern (or input pattern): a pattern of atomic stimuli each associated to an atomic region of the presentation space. (Each presentation tessellates its presentation space in a sum of atomic regions, depending on the granularity of the sensory system).

• Each atomic stimulus consists of a bundle of sensory quality values (qualia) related to an atomic region of timespace (e.g., there is red, here; it is soft and white, here).

• Domain elements corresponds to invariants within and across presentation patterns

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From experience to conceptualization

1998:

2008:

relevant invariants across world’s moments: D,

Conceptualization

State of affairsState of

affairsPresentationpatterns

Perception

relevant invariants within and across

presentation patterns:D,

Conceptualization Reality

Phenomena

Domain ofDiscourse

D

State of affairsState of

affairsState of D's affairs

cognitive domain (different from domain of discourse)!

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Possible worlds as presentation patterns(or sensory states)

Presentation pattern: unique (maximal) pattern of qualia ascribed to a spatiotemporal region tessellated at a certain granularity

...This corresponds to the notion of state for a sensory system (maximal combination of values for sensory variables)

Possible worlds are (for our purposes)

sensory states

(or if you prefer, sensory situations)

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Constructing the cognitive domain

• Synchronic level: topological/morphological invariants within a single presentation pattern • Unity properties are verified on presentation patterns on the basis

of pre-existing schemas: topological and morphological wholes (percepts) emerge

• Diachronic level: temporal invariants across multiple presentation patterns• Objects: equivalence relationships among percepts belonging to

different presentations are established on the basis of pre-existing schemas

• Events: unity properties are ascribed to percept sequences belonging to different atomic presentations

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The basic ingredients of a conceptualization (simplified view)

• cognitive objects: mappings from presentation patterns into their parts

• for every presentation, such parts constitute the perceptual reification of the object.

• concepts and conceptual relations: functions from presentation patterns into sets of (tuples of) cognitive objects

• if the value of such function (the concept’s extension) is not an empty set, the correponding perceptual state is a (positive) example of the given concept

• Rigid concepts: same extension for all presentation patterns (possible worlds)

Ontology

Language L

Intended models for each IK(L)

Ontological commitment K (selects D’D and ’)

Interpretations I

Ontology models

Models MD’(L)

Bad Ontology

~Good

relevant invariants across presentation

patterns:D,

Conceptualization

State of affairsState of

affairsPresentationpatterns

Perception Reality

Phenomena

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Ontology Quality: Precision and Coverage

Low precision, max coverage

Less good

Low precision, limited coverage

WORSE

High precision, max coverage

Good

Max precision, limited coverage

BAD

When precision is not enough

Only one binary predicate in the language: on

Only three blocks in the domain: a, b, c.Axioms (for all x,y,z):

on(x,y) -> ¬on(y,x)

on(x,y) -> ¬z (on(x,z) on(z,y))

Non-intended models are excluded, but the rules for the competent usage of on in different

situations are not captured.

Excluded conceptualizations

acb

aIndistinguishable conceptualizations

ac

ac

a

c

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The reasons for ontology inaccuracy

• In general, a single intended model may not discriminate

between positive and negative examples because of a

mismatch between:

• Cognitive domain and domain of discourse: lack of entities

• Conceptual relations and ontology relations: lack of primitives

• Capturing all intended models is not sufficient for a “perfect”

ontology

Precision: non-intended models are excluded

Accuracy: negative examples are excluded

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Kinds of ontology change(to be suitably encoded in versioning systems!)

• Reality changes • Observed phenomena

• Perception system changes • Observed qualities (different qualia)• Space/time granularity• Quality space granularity

• Conceptualization changes• Changes in cognitive domain• Changes in conceptual relations

• metaproperties like rigidity contribute to characterize them (OntoClean assumptions reflect a particular conceptualization)

• Logical characterization changes• Domain• Vocabulary• Axiomatization (Correctness, Coverage, Precision)• Accuracy

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Perception as a metaphor for the initial phase of conceptual modeling

• Is student a rigid concept?• If you look at possible worlds, in the common understanding

of this notion, your answer is no (it is rather antirigid: it is always possible to be a non-student)

• If you focus your “perception” on a restricted point of view, then it may turn out to be rigid (in terms of the “possible worlds” you are able to perceive)