Computing Capabilities of Mediators
description
Transcript of Computing Capabilities of Mediators
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