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
Querying Ontology Based Database Using
OntoQLStephane Jean et al.
Presented by: Meher Talat Shaikh
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
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
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
Ontology kernel
Ontology example
Ontology class example
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
Content cont..
Relationship between ontology and content is defined by partial function nomination: CEXTENT
Classes without extensional definition are said to be abstract
Content example
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
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.
OntoQL DDL
Laboratory example
Querying OBDB
example queries
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
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.
Advantages of OntoQL
Based on SQL
Allows schema manipulation
Express queries in different languages.
Provides GROUP BY and ORDER By operators.
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.
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.
Thank you.