Integrating View Schemata Using an Extended Object Definition Language

Integrating View Schemata Integrating View Schemata Using an Extended Using an Extended

Object Definition LanguageObject Definition Language

Mark RoantreeMark Roantree

Dublin City UniversityDublin City University

6th International IFCIS Conference on Cooperative Information Systems (CoopIs 2001) Slide 2

ContentContent

IntroductionIntroduction Background, Problem & MotivationBackground, Problem & Motivation View Concepts & Language OverviewView Concepts & Language Overview View Language UsageView Language Usage Generation of Virtual Class ExtentsGeneration of Virtual Class Extents Implementation & ConclusionsImplementation & Conclusions


IntroductionIntroduction

Federated Database SystemsFederated Database Systems– Heterogeneous Information Systems Heterogeneous Information Systems

communicate through a common (ODMG) communicate through a common (ODMG) interface.interface.

– Each system specifies data Each system specifies data viewsviews to share to share with other systems.with other systems.

– A view is a A view is a subschemasubschema of virtual classes. of virtual classes.

– An An Integration ServiceIntegration Service imports views and imports views and combines them to form a federated view.combines them to form a federated view.


Oracle 8

Legacy

Informix

Versant

ODMGview

ODMGview

ODMGview

ODMGview

IntegrationService

ODMG Federated Schema


BackgroundBackground

The OASIS Project: research into building The OASIS Project: research into building a healthcare prototype.a healthcare prototype.

Six information systems to share data in Six information systems to share data in the HIV department of a Dublin hospital.the HIV department of a Dublin hospital.

Forward interoperability is a Forward interoperability is a requirement.requirement.

Four of these systems may participate in Four of these systems may participate in alternate federations.alternate federations.


Problem & MotivationProblem & Motivation

Global database imports locally defined Global database imports locally defined views.views.

Specific views are selected to comprise Specific views are selected to comprise each federated schema.each federated schema.

To support forward interoperability, the To support forward interoperability, the usage of a standard model is important.usage of a standard model is important.

ODMG is a published standard which ODMG is a published standard which supports the necessary o-o features.supports the necessary o-o features.

A semantically rich model helps integration A semantically rich model helps integration engineers to “understand” each schema.engineers to “understand” each schema.


Problem & MotivationProblem & Motivation

ProblemProblem– ODMG has no view mechanism.ODMG has no view mechanism.

Requirements:Requirements:– View mechanism must:View mechanism must:– retain as much semantic information as retain as much semantic information as

possible;possible;– easily facilitate complex restructuring (o-o easily facilitate complex restructuring (o-o

model is not as simple as the relational model is not as simple as the relational model);model);

– support schema integration.support schema integration.


View ConceptsView Concepts

A A viewview is a is a subschemasubschema comprising one or more comprising one or more (multi-class) segments.(multi-class) segments.

A A segmentsegment comprises one or more classes comprises one or more classes connected through either inheritance or connected through either inheritance or association relationships.association relationships.

Each segment contains Each segment contains aa pivotalpivotal class which class which determines the extent for all classes in that determines the extent for all classes in that segment.segment.

No new object identifiers are created i.e. an No new object identifiers are created i.e. an object preserving semantics with tight bindings object preserving semantics with tight bindings between virtual and base classes.between virtual and base classes.


Language OverviewLanguage Overview

Property Declarations:Property Declarations:– renamerename– hidehide– derivederive

Class DeclarationsClass Declarations– operation (restructure & integrate)operation (restructure & integrate)– renamerename– ffilterilter

The ODLThe ODLvv language is an extension to ODMG’s language is an extension to ODMG’s ODL.ODL.


Property DeclarationsProperty Declarations

SubschemaSubschema PASlocal1 { PASlocal1 {SchemaSegmentSchemaSegment { {ImportBaseImportBase Patient, Consultant; Patient, Consultant;RestructureRestructure { {useuse Patient Patientpropertyproperty { { renamerename Fname Fname asas Firstname Firstname hidehide DOB,Bloodtype,NextOfKin DOB,Bloodtype,NextOfKin derivederive cm_height cm_height asas height * 2.5 } height * 2.5 }}}ExportExport PASlocal1.Patient, PASlocal1.Patient, PASlocal1.Consultant; PASlocal1.Consultant; }}

}}


Class RestructuringClass Restructuring

aggregate operatoraggregate operator

Patient

MRN

Quantity

Date_in

EpisodeRef

Date

Details

Patient

MRN

Quantity

Date_in

EpisodeRef

Episodes

EpisodeRef

Date

Details

PatientRef

Episodes := aggregate (EpisodeRef,Date,Details)from Patient {as EpisodeRef to PatientRef}

expand Patient.EpisodeRef (reverse operation)


Class RestructuringClass Restructuring subclass, superclass operatorssubclass, superclass operators

Fname

Lname

DOB

MRN

NextOfKin

bloodtype

consultant

Address

Episodes

Fname

Lname

DOB

Address

MRN

NextOfKin

bloodtype

consultant

Episodes

Patient Person

Patient

Person := superclass (Fname,Lname,DOB,Address)from Patient

flatten Patient into Personrename Person as Patient(reverse operation)


Restructuring SampleRestructuring Sample

subschemasubschema Agg AggFed1 Fed1 {{SchemaSegmentSchemaSegment {{ ImportImportVirtualVirtual PAS1.Patient; PAS1.Patient; RestructureRestructure { { useuse PAS1.Patient PAS1.Patient classclass { { Episodes := Episodes := aggregateaggregate

(EpisodeRef, Date, Details)(EpisodeRef, Date, Details)fromfrom Patient Patientasas EpisodeRef EpisodeRef toto PatientRef PatientRef }}

};}; ExportExport Agg AggFed1Fed1.Patient, Agg.Patient, AggFed1Fed1.Episodes.Episodes };};

};};


Integration operatorIntegration operator

join, ojoinjoin, ojoin

Patient

Fname

Lname

MRN

DOB

Address

Patient

Firstname

Lastname

DOB

PatientID

bloodtype

Patient

Fname

Lname

PatientID

DOB

Address

bloodtype

PAS database HIV database

Property Mapping


Using joinUsing join

How How to deal with synonymsto deal with synonyms??– Use Use linklink to bind two properties to bind two properties..

What happens if all four semantically What happens if all four semantically relatedrelated properties are not equal? properties are not equal?– ObjectsObjects are not are not a member of the extent for a member of the extent for

thethe new virtual class new virtual class oror– Use Use preferprefer to choose one value to choose one value oror– Use Use withwith to amend the contents of one to amend the contents of one

property so that the property pair becomes property so that the property pair becomes equal.equal.


join sample (i)join sample (i)

classclass { { joinjoin Patient Patient fromfrom PAS.Patient, HIV.Patient PAS.Patient, HIV.Patient onon P PASAS.Patient.MRN.Patient.MRN linklink PatientId := MRN PatientId := MRN}}

This view will use This view will use MRNMRN and and PatientIDPatientID to perform the join to perform the join operation. operation. PatientIDPatientID is the chosen label in the view class. is the chosen label in the view class.

It will also require that both It will also require that both DOBDOB properties match, properties match, otherwise the objects will not form part of the view otherwise the objects will not form part of the view class class extent.extent.

Name properties (Name properties (eg. eg. FnameFname and and FirstnameFirstname) are treated ) are treated as unrelated properties.as unrelated properties.


join sample (ii)join sample (ii)

classclass { { joinjoin Patient Patient fromfrom PAS.Patient, HIV.Patient PAS.Patient, HIV.Patient onon Pas.Patient.MRN Pas.Patient.MRN linklink PatientId := MRN PatientId := MRN linklink Fname := Firstname Fname := Firstname linklink Lname := Lastname Lname := Lastname}}

This view will expect that This view will expect that FnameFname and and FirstnameFirstname are are equal otherwise objects will not form part of the view equal otherwise objects will not form part of the view class class extent.extent.

The term after the The term after the linklink statement is used in the view statement is used in the view class (class (FnameFname, , LnameLname).).


join sample (iii)join sample (iii)

classclass { {

joinjoin Patient Patient fromfrom PAS.Patient, HIV.Patient PAS.Patient, HIV.Patient

onon Pas.Patient.MRN Pas.Patient.MRN

linklink PatientId := MRN PatientId := MRN

linklink Fname := Firstname Fname := Firstname

linklink Lname := Lastname Lname := Lastname

withwith Fname Fname preferprefer PAS.Fname PAS.Fname

withwith Lname Lname preferprefer PAS.Lname PAS.Lname

}}

Where names do not match, values frWhere names do not match, values froom the PAS database are m the PAS database are chosen.chosen.

Note that the Note that the DOBDOB properties must properties must still still match.match.


Integration operatorIntegration operator superjoin, osuperjoinsuperjoin, osuperjoin

Patient

Fname

Lname

MRN

DOB

Address

Patient

Firstname

Lastname

DOB

PatientID

bloodtype

Patient

Firstname

Lastname

DOB

MRN

H_Patient

bloodtype

P_Patient

Address


Class FiltersClass Filters

A filter function A filter function f()f() is applied to a is applied to a pivotalpivotal class. class.

ThThee filter function is used to create the filter function is used to create the extents for all classes in that segment extents for all classes in that segment of the schema.of the schema.

A filter is an OQL A filter is an OQL wherewhere clause. clause.

filterfilter Patient where bloodtype = ‘A’ Patient where bloodtype = ‘A’


Generation of ExtentsGeneration of Extents

How are extents for base classes generated?How are extents for base classes generated? A A shallowshallow extent E extent Ess(C) is the set of all objects for (C) is the set of all objects for

the class the class CC. The extent query for this class is . The extent query for this class is ““select *.*select *.*”.”.

A A deepdeep extent E extent Edd(C) is the set of all objects for (C) is the set of all objects for the class the class CC, plus the deep extents for all of its , plus the deep extents for all of its sub-classes Ssub-classes Sii..

EEdd(C) = E(C) = Ess(C) (C) EEdd(S(Sii) )

ii


Virtual Class ExtentsVirtual Class Extents

Let VC be the Virtual Class and f() Let VC be the Virtual Class and f() be be the filter function applied to that class.the filter function applied to that class.

EEdd(f(VC)) = E(f(VC)) = Ess(f(VC)) (f(VC)) EEdd(f(fii(VS(VSii))))

ii

A different filter function is generated A different filter function is generated for each class based on the filter for the for each class based on the filter for the pivotal class.pivotal class.


ImplementationImplementation

ODMG metamodel was extended to hold ODMG metamodel was extended to hold virtual entities (new metaclasses). virtual entities (new metaclasses).

Versant OOdb was used to store ODMG Versant OOdb was used to store ODMG representations of local Information representations of local Information Systems.Systems.

Java/ANTLR was used to construct parser Java/ANTLR was used to construct parser for view and wrapper definitions.for view and wrapper definitions.

Visual C++ 6.0 used to implement the Visual C++ 6.0 used to implement the semantic actions for each view command.semantic actions for each view command.


user-definedobject instances

ODMG-defined metadata types

(describe database schema)

Extension metadata types(describe view schemata

& object wrappers

Database Schema Repository Schema

Local IS

Database ODLProcess

Model TransformationProcess

ODLfile

wrapperdefinition

viewdefinition

ViewService

WrapperService


ConclusionsConclusions

Research into federated databases has Research into federated databases has proposed an o-o canonical model.proposed an o-o canonical model.

ODMG provides a standard solution but ODMG provides a standard solution but does not support virtual classes and does not support virtual classes and properties, or view schemata.properties, or view schemata.

The ODLThe ODLvv and ODL and ODLww languages languages overcome this problem, with the overcome this problem, with the inclusion of rich semantics.inclusion of rich semantics.

Carefully crafted views allow updates Carefully crafted views allow updates for some federations.for some federations.

Documents

Integrating View Schemata Using an Extended Object Definition Language