Capability-Based Optimization in Mediators

Capability-Based Optimization in Mediators

Rohit Deshmukh

ID 120

CS-257

Rohit Deshmukh

ID 120

CS-257

Modes of Information IntegrationModes of Information Integration

1. Federated Collection1. Federated Collection

DB1 DB2

DB3 DB4

Sources are Independent, but one source can call on others to supply Information

Modes of Information IntegrationModes of Information Integration

2. Data Warehousing2. Data WarehousingCopies of data from several sources are stored in a single database, called Data Warehouse.

Warehouse

User Query

Result

Combiner

Extractor Extractor

Source1 Source2

Modes of Information IntegrationModes of Information Integration

3. Mediation3. Mediation

Mediator

Wrapper Wrapper

Source1 Source2

query result

A mediator is a software component that supports a virtual database.

Capability-Based Optimization in Mediators

Capability-Based Optimization in Mediators

Problem of Limited Source Capabilities Many useful sources have only Web-based interfaces Web sources usually permit querying only through a query

form Legacy systems(designed to be queried in specific way) Reasons of security Indexes on large databases may make certain kinds of queries

feasible while others too expensive

Problem of Limited Source Capabilities Many useful sources have only Web-based interfaces Web sources usually permit querying only through a query

form Legacy systems(designed to be queried in specific way) Reasons of security Indexes on large databases may make certain kinds of queries

feasible while others too expensive

Capability-Based Optimization in Mediators

Capability-Based Optimization in Mediators

Notation for Describing Source Capabilities f (free) The attribute can be specified or not. b(bound) We must specify a value for the attribute, any

value is allowed. u(unspecified) we are not permitted to specify value for

the attribute c[S] choice from set S o[S] optional from set S We place a prime e.g. b’ on a code if the attribute

is not a part of the output query.

Notation for Describing Source Capabilities f (free) The attribute can be specified or not. b(bound) We must specify a value for the attribute, any

value is allowed. u(unspecified) we are not permitted to specify value for

the attribute c[S] choice from set S o[S] optional from set S We place a prime e.g. b’ on a code if the attribute

is not a part of the output query.

Notation for Describing Source Capabilities

Notation for Describing Source Capabilities

Example Dealer 1 is a source of data in the form

Cars(SerialNo, model, color, autoTrans, cdPlayer)

Two possible ways that Dealer 1 might allow to be queried

1. b’uuuu

2. ubbo[yes,no]o[yes,no]

• Alternative adornment, suppose that queries limit the model and color attributes to valid values;

uc[modelx,gobi,…]c[red,blue,….]o[yes,no]o[yes,no]

Example Dealer 1 is a source of data in the form

Cars(SerialNo, model, color, autoTrans, cdPlayer)

Two possible ways that Dealer 1 might allow to be queried

1. b’uuuu

2. ubbo[yes,no]o[yes,no]

• Alternative adornment, suppose that queries limit the model and color attributes to valid values;

uc[modelx,gobi,…]c[red,blue,….]o[yes,no]o[yes,no]

f(free); b(bound); u(unspecified); c[S] ; o[S]

Capability-Based Query-Plan Selection

Capability-Based Query-Plan Selection

A capability based query optimizer first considers what queries it can ask at the sources that will help answer the query.

The bindings may make some more queries at the sources.The process is repeated until

We have asked enough queries at the sources to resolve all the conditions of the mediator queries.Such a plan is called feasible.

We can construct no more valid forms of source queries. In which case the mediator must give up.

A capability based query optimizer first considers what queries it can ask at the sources that will help answer the query.

The bindings may make some more queries at the sources.The process is repeated until

We have asked enough queries at the sources to resolve all the conditions of the mediator queries.Such a plan is called feasible.

We can construct no more valid forms of source queries. In which case the mediator must give up.

Capability-Based Query-Plan Selection

Capability-Based Query-Plan Selection

Example Dealer 2 has two different sources.

1. Autos(serial, model, color)

2. Options(serial, option)

Assuming we have only the following adornments for the two sources.

• ubf for Autos• bu and uc [autoTrans, cdPlayer].

Example Dealer 2 has two different sources.

1. Autos(serial, model, color)

2. Options(serial, option)

Assuming we have only the following adornments for the two sources.

• ubf for Autos• bu and uc [autoTrans, cdPlayer].

f(free); b(bound); u(unspecified); c[S] ; o[S]

ExampleExample

Find the serial numbers and colors of Modelx with a CD player.

1. Select (serial,color) from Autos where model=modelx

2. Use bu for Options source

for each serial from above match;

option = CdPlayer

Find the serial numbers and colors of Modelx with a CD player.

1. Select (serial,color) from Autos where model=modelx

2. Use bu for Options source

for each serial from above match;

option = CdPlayer

f(free); b(bound); u(unspecified); c[S] ; o[S]

ExampleExample

Find the serial numbers and colors of Modelx with a CD player.

1. Query Options

Select serial from options

where option = CdPlayer

2. Now query Autos

Select (serial,colors) where

model = modelx;

3. Intersect the two sets of serial numbers.

Find the serial numbers and colors of Modelx with a CD player.

1. Query Options

Select serial from options

where option = CdPlayer

2. Now query Autos

Select (serial,colors) where

model = modelx;

3. Intersect the two sets of serial numbers.

f(free); b(bound); u(unspecified); c[S] ; o[S]

ExampleExample Find the serial numbers and colors of Modelx with a CD

player.1. Query Options as in previous case

Select serial from options where option = CdPlayer

2. Use these serial numbers to query Autos,select color where serial = (selected serial) and model = modelx This would not work because the second part, does not have a matching adornment.

A Capability-based optimizer eliminates infeasible plans such as this one.

Find the serial numbers and colors of Modelx with a CD player.

1. Query Options as in previous caseSelect serial from options where option = CdPlayer

2. Use these serial numbers to query Autos,select color where serial = (selected serial) and model = modelx This would not work because the second part, does not have a matching adornment.

A Capability-based optimizer eliminates infeasible plans such as this one.

f(free); b(bound); u(unspecified); c[S] ; o[S]