querying ontology based database using ontoql
DESCRIPTION
Querying Ontology Based Database Using OntoQL. Stephane Jean et al. Presented by: Meher Talat Shaikh. Overview. OntoQL is a language for defining, manipulating and querying data stored in an OBDB. Objective: retrieve definition, meaning, translation and/or identifier of a given data item. - PowerPoint PPT PresentationTRANSCRIPT
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Querying Ontology Based Database Using
OntoQLStephane Jean et al.
Presented by: Meher Talat Shaikh
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OverviewOntoQL is a language for defining, manipulating and querying data
stored in an OBDB.
Objective: retrieve definition, meaning, translation and/or identifier of a given data item.
OBDB (OntoDB) data model: created and customized by users
OntoQL operators that makes up OntoAlgebra
Example queries
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OBDB data modelBuilt on top of relational database model.
Both the ontology and the instances are kept in the same database.
Content part: Stores the instances
Ontology part: Stores ontology definitions
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OntologyE is a set of entities representing the ontology model
OC is the set of concepts of ontologies
A is the set of attributes describing each OC
SuperEntities: associates set of super entities to an entity (E 2E1 )
TypeOf: Associates the strongest entity to each concept of ontology (OC E)
AttributeDomain, AttributeRange
Val
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Ontology kernel
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Ontology example
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Ontology class example
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ContentEXTENT is a set of extensional definitions of ontology classes
I is the set of instances of the OBDB
TypeOf : I EXTENT
SchemaProp : EXTENT 2P
Val
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Content cont..
Relationship between ontology and content is defined by partial function nomination: CEXTENT
Classes without extensional definition are said to be abstract
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Content example
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Onto AlgebraOntoImage: returns collection of objects after applying a specific
function. OntoImage(C, IC, p)
OntoProject: allows the application of more than one function.
OntoSelect: creates a collection of objects satisfying a selection predicate.
OntoJoin: creates relationships between objects of two collections.
* : introduces polymorphism: returns the instances of the class C and all the classes subsumed by C
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OntoQLExtension of SQL
DDLto create, alter and drop concepts of ontologiesto create, alter and drop attributes of these concepts of ontologies
DMLUpdate, Insert, Delete etc.
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OntoQL DDL
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Laboratory example
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Querying OBDB
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example queries
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OntoQL FeaturesPath expressions. Associations may be traversed using dot notation.
Polymorphic query: * operator
Nested queries
Aggregate functions: count, avg, min max.
Quantification: Existential (ANY, SOME) and universal (ALL)
Set operators: Union, Intersection and Except
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Processing of ONtoQL OntoQL query is parsed into an OntoAlgebra expression tree
path expressions and * operators removed
The expression tree is optimized
OntoAlgebra is translated to relational algebra tree.
The relational algebra tree is optimized.
The optimized relational algebra trees are translated into SQL queries.
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Advantages of OntoQL
Based on SQL
Allows schema manipulation
Express queries in different languages.
Provides GROUP BY and ORDER By operators.
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Shortcomings
FROM Clause is mandatory
Does not yet support multi-instantiation capability
Large sets of data are to be evaluated to study the OntoQL scalability issue.
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Conclusion
OntoQL is effective in querying data, ontology and both
Based on Object oriented concepts and RDB model
conceptual model may be created and customized by users.
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Thank you.