Computing Computing Capabilities of Capabilities of

MediatorsMediators

Ramana YerneniRamana YerneniChen LiChen Li

Hector Garcia-MolinaHector Garcia-MolinaJeffrey UllmanJeffrey Ullman

Wrapper ArchitectureWrapper Architecture

Mediator Catalog

Wrapper Wrapper

Data Source Data Source Data Source Data Source

User Query

ScopeScope

Framework for expressing source Framework for expressing source capabilitiescapabilities

Approach for computing mediator Approach for computing mediator capabilitiescapabilities

Extending mediator capabilitiesExtending mediator capabilities

PathwayPathway

Capabilities of data sourcesCapabilities of data sources Simple mediatorsSimple mediators Advanced techniques in Advanced techniques in

mediatorsmediators Dynamic mediatorsDynamic mediators Concise capability descriptionConcise capability description

Capabilities of Data Capabilities of Data SourcesSources Attribute Adornments:Attribute Adornments:

– Adornment Adornment f f :: for freefor free– Adornment Adornment uu : : for unspecifiablefor unspecifiable– Adornment Adornment bb : : for boundfor bound– Adornment Adornment c[s] c[s] :: for compulsory for compulsory

constantconstant– Adornment Adornment o[s]o[s] : : for optionalfor optional

constantconstant

Capabilities of Data Capabilities of Data SourcesSources

R(X Y Z) {b u f }R(X Y Z) {u b f }Exported Views

Data Source

R ( x1, Y, Z ) R ( X, Y, Z )

PathwayPathway

Capabilities of data sources Simple mediatorsSimple mediators Advanced techniques in Advanced techniques in

mediatorsmediators Dynamic mediatorsDynamic mediators Concise capability descriptionConcise capability description ExampleExample

Simple MediatorsSimple Mediators

Simple Mediator PropertiesSimple Mediator Properties– No post processingNo post processing– Performs joins blindlyPerforms joins blindly

Union ViewsUnion Views– Variable Adornments in Union View Variable Adornments in Union View

are computed from base view are computed from base view adornmentsadornments

– Mapping FunctionMapping Function

Simple MediatorsSimple Mediators

Mapping Function:Mapping Function:

ff o[s3]o[s3] bb c[s4]c[s4] uu

ff ff o[s3]o[s3] bb c[s4]c[s4] uu

o[s1]o[s1] o[s1o[s1]]

o[s1o[s1s3s3]]

c[s1c[s1]]

c[s1c[s1ss4]4]

uu

bb bb c[s3]c[s3] bb c[s4]c[s4] --

c[s2]c[s2] c[s2]c[s2] c[s2c[s2s3s3]]

c[s2c[s2]]

c[s2c[s2ss4]4]

--

uu uu uu -- -- uu

Union of two viewsUnion of two views– ExampleExample

Simple MediatorsSimple Mediators

R(X, Y, Z) {b f u}

Data Source

R(X, Y, Z) {f b u}

Data Source

R(X, Y, Z) { b b u }

Mediator Union View

Simple MediatorsSimple Mediators

Union of two base views with multiple Union of two base views with multiple templatestemplates– Cross product of two template setsCross product of two template sets– For each pair apply mapping functionFor each pair apply mapping function

Union of multiple base views with Union of multiple base views with multiple templatesmultiple templates– Process two base views at a timeProcess two base views at a time– Repeat (n-1) timesRepeat (n-1) times

Simple MediatorsSimple Mediators

Join ViewsJoin Views– Non-join attribute adornments are copied Non-join attribute adornments are copied

as they are in join viewas they are in join view– Join attributes are computed using Join attributes are computed using

mapping functionmapping function

R1(X,Y) {b f }

Data Source

R2(Y,Z) {b u}

Data Source

R1R2(X, Y, Z) { b b u }Mediator Join View

Simple MediatorsSimple Mediators

Selection ViewsSelection Views– Pass the query to underlying data source as Pass the query to underlying data source as

it is if it fits the templateit is if it fits the template– Filter the results according to selection Filter the results according to selection

predicatespredicates

Projection ViewsProjection Views– Hidden attributes are left unspecifiedHidden attributes are left unspecified– Works only if hidden attribute adornments Works only if hidden attribute adornments

are are f, u, of, u, o

PathwayPathway

Capabilities of data sources Simple mediatorsSimple mediators Advanced techniques in Advanced techniques in

mediatorsmediators Dynamic mediatorsDynamic mediators Concise capability descriptionConcise capability description

Advance Techniques in Advance Techniques in MediatorsMediators Union ViewsUnion Views

– Post processingPost processing Filter the input query to fit source viewsFilter the input query to fit source views Post process the results to match user Post process the results to match user

requirementsrequirements

– Union view adornments are Union view adornments are computed using Mapping functioncomputed using Mapping function

Advance Techniques in Advance Techniques in MediatorsMediators Union View ExampleUnion View Example

R(X,Y,Z){b f u }

Data Source

R(X,Y,Z){b u f }

Data Source

R(X, Y, Z) { b u u }Mediator Union View

R(x1,y1,z1)

R(x1,y1,Z)

R(x1,Y,z1)

b f f }

Advance Techniques in Advance Techniques in MediatorsMediators

ff o[s3]o[s3] bb c[s4]c[s4] uu

ff ff ff bb c[s4]c[s4] ff

o[s1o[s1]]

ff ff bb c[s4]c[s4] bb

b b b b bb bb c[s4]c[s4] bb

c[s2c[s2]]

c[s2]c[s2] c[s2c[s2s3s3]]

c[s2c[s2]]

c[s2c[s2ss4]4]

c[s2]c[s2]

uu ff ff bb c[s4]c[s4] ff

Advance Techniques in Advance Techniques in MediatorsMediators Join ViewsJoin Views

– Non-join attribute adornments are Non-join attribute adornments are copied as they arecopied as they are

– Passing join attribute bindings from Passing join attribute bindings from left to right viewleft to right view

– Join attribute adornments are Join attribute adornments are computed using mapping functioncomputed using mapping function

Advance Techniques in Advance Techniques in MediatorsMediators Join views: passing bindingsJoin views: passing bindings

R1(X,Z){b f }

Data Source

R2(Z,V){b f }

Data Source

R(X, Z, V) { b b f }Mediator Join View

R(x1,Z,V)

R(x1,Z) R(z1,V)

{ b f f }

PathwayPathway

Capabilities of data sources Simple mediatorsSimple mediators Advanced techniques in Advanced techniques in

mediatorsmediators Dynamic mediatorsDynamic mediators Concise capability descriptionConcise capability description

Dynamic MediatorsDynamic Mediators

Liberal templatesLiberal templates– Answerability depends on state of Answerability depends on state of

data in data sourcedata in data source– Can’t be always answeredCan’t be always answered

Conservative templatesConservative templates– Can always be answeredCan always be answered– Computed using techniques Computed using techniques

discussed in earlier slidesdiscussed in earlier slides

Dynamic MediatorsDynamic Mediators

Liberal Template ExampleLiberal Template Example

R1(X,Y){b f }

Data Source

R2(Y,Z){c[s] f }

Data Source

R(X, Y, Z) { b c[s] f }Mediator Join View

R(x1,Y,Z)

R1(x1,Y) R(y1,Z)

{ b f f }

Dynamic MediatorsDynamic Mediators

Simple MediatorsSimple Mediators Mediators employing advanced Mediators employing advanced

techniquestechniques– Post ProcessingPost Processing– Passing bindingsPassing bindings

Dynamic mediatorsDynamic mediators– Liberal TemplatesLiberal Templates

PathwayPathway

Capabilities of data sources Simple mediatorsSimple mediators Advanced techniques in Advanced techniques in

mediatorsmediators Dynamic mediatorsDynamic mediators Concise capability descriptionConcise capability description

Concise Capability Concise Capability DescriptionDescription Mediator view space is exponentialMediator view space is exponential k templates per view, n sourcesk templates per view, n sources

– View space will be kView space will be knn

Large number of templates are Large number of templates are redundantredundant– M1(M1(b f b b f b ) and M2() and M2(f f f f f f ) : ) :

M2 is redundant M2 is redundant

Concise Capability Concise Capability DescriptionDescription Adornment GraphAdornment Graph

b

C[s1]

O[s2]

u

f

Concise Capability Concise Capability DescriptionDescription Subsumption testSubsumption test

– Template T subsumes T1 iff Template T subsumes T1 iff Every attribute x in T1 is atleast as Every attribute x in T1 is atleast as restrictive as Trestrictive as T

Subsumption test partitions the Subsumption test partitions the set of templatesset of templates

Select the template which Select the template which subsumes all other templates in a subsumes all other templates in a partitionpartition

PathwayPathway

Capabilities of data sources Simple mediatorsSimple mediators Advanced techniques in Advanced techniques in

mediatorsmediators Dynamic mediatorsDynamic mediators Concise capability descriptionConcise capability description