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ISIT315: Semantic Web > 07: Web Ontology Language: OWL > Flashcards

07: Web Ontology Language: OWL Flashcards

1
Q

A reasoner expands the ____ ____ ____ based on ____ like rdfs:subClassOf, rdfs:range, rdfs:domain, etc.

A

A reasoner expands the number of triples based on relations like rdfs:subClassOf, rdfs:range, rdfs:domain, etc.

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2
Q

Five Requirements of Any Ontology Language

A
  1. A well-defined syntax
  2. Efficient reasoning support
  3. A formal semantics
  4. Sufficient expressive power
  5. Convenience of expression
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3
Q

What is the tradeoff between expressive power and efficient reasoning support? What compromise must be taken?

A

the richer the language, the more inefficient the reasoning support

Compromise:

  • on one hand, a language supported by reasonable efficient reasoners
  • on the other hand, a language that can express large classes of ontologies and knowledge
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4
Q

Class Membership

(Reasoning About Knowledge in Ontology Languages)

A

If x is an instance of a class C, and C is a subclass of D, then we can infer that x is an instance of D

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5
Q

Equivalence of Classes

(Reasoning About Knowledge in Ontology Languages)

A

If class A is equivalent to class B, and class B is equivalent to class C, then A is equivalent to C, too

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6
Q

Consistency

(Reasoning About Knowledge in Ontology Languages)

A

X instance of classes A and B, but A and B are disjoint

* this is an indication of an error in the ontology

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7
Q

Classification

(Reasoning About Knowledge in Ontology Languages)

A

Certain property-value pairs are a sufficient condition for membership in a class A; if an individual x satisfies such conditions, we can conclude that x must be an instance of A

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8
Q

Uses for Reasoning

A

Reasoning support is important for:

  • checking the consistency of the ontology and the knowledge
  • checking for unintended relationships between classes
  • automatically classifying instances in classes

Checks like the preceding ones are valuable for:

  • designing large ontologies, where multiple authors are involved
  • integrating and sharing ontologies from various sources
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9
Q

Reasoning Support for OWL

A
  • Semantics is a prerequisite for reasoning support
  • Formal semantics and reasoning support are usually provided by
    • mapping an ontology language to a known logical formalism
    • using automated reasoners that already exist for those formalisms
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10
Q

OWL is (partially) mapped on a _____ logic, and makes use of reasoners such as ____ and ____.

A

OWL is (partially) mapped on a description logic, and makes use of reasoners such as FaCT and RACER.

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11
Q

Combining RDF Schema with ____ leads to uncontrollable ____ properties.

A

Combining RDF Schema with logic leads to uncontrollable computational properties.

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12
Q

The Five Major Limitations of the Expressive Power of RDF Schema in Comparison with OWL

A
  1. Local scope of properties
    • ​​e.g. cannot declare range restrictions that apply to some classes only like a cow can only eat plants, but other animals can eat meat too
  2. Disjointness of classes
    • ​​e.g. cannot disjoint classes, like graduate vs undergraduate
  3. Boolean combinations of classes
    • ​​e.g. cannot combine classes using union, intersection, complement
  4. Cardinality restrictions
    • ​​e.g. cannot state a person has exactly two parents, or a course has exactly one lecturer
  5. Special characteristics of properties
    • ​​e.g. cannot state transitive, unique, or inverse properties
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13
Q

Three Species of OWL

A
  1. OWL Full
  2. OWL DL
  3. OWL Lite
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14
Q

OWL Full

(Three Species of OWL)

A
  • Uses all the OWL languages primitives
  • Allows the combination of these primitives in arbitrary ways with RDF and RDF Schema
  • Fully upward-compatible with RDF, both syntactically and semantically
  • So powerful that it is undecidable
    • No complete (or efficient) reasoning support
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15
Q

OWL DL

(Three Species of OWL)

A
  • Sublanguage of OWL Full that restricts application of the constructors from OWL and RDF
    • Application of OWL’s constructors to each other is disallowed
    • Therefore it corresponds to a well studied description logic
  • Permits efficient reasoning support
  • But we lose full compatibility with RDF:
    • Not every RDF document is a legal OWL DL document.
    • Every legal OWL DL document is a legal RDF document.
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16
Q

OWL Lite

(Three Species of OWL)

A
  • An even further restriction limits OWL DL to a subset of the language constructors
    • e.g. OWL Lite excludes enumerated classes, disjointness statements, and arbitrary cardinality.
  • The advantages of this is a language that is easier to
    • grasp, for users
    • implement, for tool builders
  • The disadvantage is restricted expressivity
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17
Q

Upward Compatibility between OWL Species

A
  • Legal OWL Lite ontology = Legal OWL DL ontology
  • Legal OWL DL ontology = Legal OWL Full ontology
  • Valid OWL Lite conclusion = Valid OWL DL conclusion
  • Valid OWL DL conclusion = Valid OWL Full conclusion
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18
Q

Semantic Web design aims at ____ ____ with corresponding reuse of software across the various layers

A

Semantic Web design aims at downward** **compatibility with corresponding reuse of software across the various layers

19
Q

The advantage of full downward compatibility for OWL is only achieved for ____ ____, at the cost of ____ ____

A

The advantage of full downward compatibility for OWL is only achieved for OWL** **Full**, at the cost of **computational intractability

20
Q

OWL Syntactic Varieties​

A

Other syntactic forms for OWL have also been defined:

  • An alternative, more readable XML-based syntax
  • An abstract syntax, that is much more compact and readable than the XML languages
  • A graphic syntax based on the conventions of UML
21
Q

Write the syntax of an OWL XML/RDF header.

A
22
Q

owl:imports is a ____ property

A

owl:imports is a transitive property

23
Q

Classes are defined using ____

(OWL RDF/XML Syntax)

A

Classes are defined using owl:Class

24
Q

Disjointness is defined using ____

(OWL RDF/XML Syntax)

A

Disjointness is defined using owl:disjointWith

25
Q

____ defines equivalence of classes

(OWL RDF/XML Syntax)

A

owl:equivalentClass defines equivalence of classes

26
Q

____ is the most general class, which contains everything

(OWL RDF/XML Syntax)

A

owl:Thing is the most general class, which contains everything

27
Q

____ is the empty class

(OWL RDF/XML Syntax)

A

owl:Nothing is the empty class

28
Q

The Two Properties of OWL

A
  • Object properties, which relate objects to other objects
    • e.g. is-TaughtBy, supervises
  • Data type properties, which relate objects to datatype values
    • e.g. phone, title, age, etc.
29
Q

Data Type Properties

(The Two Properties of OWL)

A

OWL makes use of XML Schema data types, using the layered architecture of the Semantic Web

30
Q

Object Properties

(The Two Properties of OWL)

A

user-defined data types

31
Q

____ defines inverse properties

(OWL RDF/XML Syntax)

A

owl:inverseOf defines inverse properties

32
Q

____ defines equivalent properties

(OWL RDF/XML Syntax)

A

owl:equivalentProperty defines equivalent properties

33
Q

Property Restrictions

A
  • A (restriction) class is achieved through an owl:Restriction element
  • This element contains an owl:onProperty element and one or more restriction declarations
  • One type defines cardinality restrictions
  • The other type defines restrictions on the kinds of values the property may take
    • owl:allValuesFrom specifies universal quantification
      • ∀ (the universal quantifier symbol)
    • owl:hasValue specifies a specific value
    • owl:someValuesFrom specifies existential quantification
      • ∃ (read: “there exists”).
34
Q

True or False: An owl:Restriction element can contain only one restriction declaration

A

False

* can contain one or more restriction declarations

35
Q

Write the equivalence of the following in English.

A

Only professors teach first-year subjects.

36
Q

Write the equivalence of the following in English.

A

One of the math courses is taught by #949352.

37
Q

Write the equivalence of the following in English.

A

Some tutors teach undergraduate courses.

38
Q

What element do you use to specify a minimum and maximum number?

A

owl:minCardinality and owl:maxCardinality

39
Q

How do you specify a precise number by using cardinality restrictions?

A

Use the same minimum and maximum number

40
Q

Special Properties

A
  • owl:TransitiveProperty (transitive property)
    • e.g. “has better grade than”, “is ancestor of”
  • owl:SymmetricProperty (symmetry)
    • e.g. “has same grade as”, “is sibling of”
  • owl:FunctionalProperty defines a property that has at most one value for each object
    • e.g. “age”, “height”, “directSupervisor”
  • owl:InverseFunctionalProperty defines a property for which two different objects cannot have the same value
41
Q

Write three examples for each of transitive and symmetric properties.

A

SYMMETRIC:

  1. “X isMarriedTo Y” means “Y isMarriedTo X”.
  2. “Z equals D“ means “D equals Z“
  3. ” A co-worker-of B” means “ B co-worker-of A”

TRANSITIVE:

  1. If A implies B and B implies C, then A implies C
  2. If “Z equals D” and “D equals E” means “Z equals E“
  3. If “X sub-set-of Y” and “Y sub-set-of Z” means “X sub-set Z“
42
Q

The ____ construct selects all individuals from the domain of discourse that do not belong to a certain ____. Usually, this refers to a very large set of individuals.

A

The complementOf construct selects all individuals from the domain of discourse that do not belong to a certain class. Usually, this refers to a very large set of individuals.

43
Q

Assuming #staffMember, #faculty (green), and #techSupportStaff” (blue) have all been defined as classes, by the use of nesting Boolean operators, complete the following code for defining adminStaff (red).

Hint:

#staffMember = #adminStaff + #faculty + #techSupportStaff

A

ISIT315: Semantic Web (14 decks)

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