Mar 27, 2008 Christiano Santiago 1

Schema Matching

Matching Large XML SchemasErhard Rahm, Hong-Hai Do, Sabine Maßmann

Putting Context into Schema MatchingPhilip Bohannon, Eiman Elnahrawy, Wenfei Fan, Michael Flaster

COMA - A System for Flexible Combination of Schema Matching ApproachesHongai-Hai Do, Erhard Rahm

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Goals

Introductory concepts on Schema Matching Context-Sensitive versus Context-Insensitive Complexity on XSD schemas

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Agenda

Terminology Different Approaches XML Schema Definition Context-Insensitive Context-Sensitive Q&A

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Terminology

Schema matching: it is the process of identifying that two objects are semantically related.

Mapping: it refers to the transformations between the objects.

Meaning

Conversion

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Terminology

Student.Name ≈ GradStudent.Name

Student.SSN ≈ GradStudent.ID

Student.Marks ≈ GradStudents.Grades

StudentName, SSN, Level,

Major, Marks

GradStudentName, ID, Major,

Grades

Match

Match

Transformation

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Schema Matching

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Context

Context-insensitive Context-sensitive

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Different Approaches

Schema-level matchers Instance-level matchers Hybrid matchers Reusing matching information

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Schema-Level Matchers

Only consider schema information Name Description Data type Relationship Constraints Number of nesting levels

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Instance-Level Matchers

Use instance-level to gather insight into the content and meaning of schema elements Linguistic

Dept DeptName EmpName

Constraints 416-7362100 M3J1P3

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Hybrid-Level Matchers

Combines more than one approach

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Reusing Matching Information

Use previous matching information for future matching tasks Structures or substructures often repeat

Caution Salary & Income

Payroll Tax Reporting

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XML Schema Definition (XSD)

Data types 19 built-in primitive data types 25 built-in derived data types User defined complex types

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Complex type definition: <complexType name="myNewNameType">

<complexContent> <restriction base="anyType"> <sequence>

<element name="name" type="string" /> <element name="location" type="string" />

</sequence> <attribute name="position" type="string" /> </restriction> </complexContent> </complexType>

<element name="employee" type="dc:myNewNameType" />

<dc:employee position="trainer"> <dc:name>Don Smith</dc:name> <dc:location>Dallas, TX</dc:location> </dc:employee>

XML Schema Definition (XSD)

Attribute

ChildElements

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XML Schema Definition (XSD)

Shared schema components

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XML Schema Definition (XSD)

Match Systems approaches COMA: path-based Cupid: materialized

Scalability issue: XCBL Order schema contains 1451 components, including 91 shared types. After resolving the shared components, 26000+ nodes/paths were identified.

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XML Schema Definition (XSD)

Distributed schemas XSD allows a schema to be distributed

over several schema documents (.xsd files) and namespaces

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XML Schema Definition (XSD)

Determining similarity between and

matching complex types can be as difficult

as matching two complete schemas.

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Standard Schema Matching Context-Insensitive

Matchers Matching algorithms to compute similarity

scores between a pair of attributes Weights

Scores are weighted Confidence scores are identified based on

standard statistical techniques Selection of best matches

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Fragmented-Based Schema Matching Context-Insensitive

Fragment identification Identifying fragment-pair candidates Fragment matching Result combination

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Prototype

Based on COMA: COmbining MAtch algorithm Support to multiple file schema Multiple matching strategies Fragment-based approach Result combination

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COMA

Schema representation

Schemas are represented by rooted DAGs (Directed Acyclic Graphs).

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COMA

Directed Acyclic Graphs

Direct graph With no cycles Part tree & part graph Used in Critical Path Analysis,Expression Tree

Evaluation and Game Evaluation

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COMA

Match processing

reusability

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Continuity of this work

2004: COMA prototype 2005: COMA++, extended previous COMA

prototype High quality and fast execution times Default combination of 4 matchers

2007: MOMA: Mapping-based Object Matching

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Context Schema MatchingContext-Sensitive

False Negatives

Rs.price.price → RT.music.priceRs.price.price → RT.music.sale

RS.price.prcode = “reg”

RS.price.prcode = “sale”

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Context Schema MatchingContext-Sensitive

Two techniques for selecting contextual matches:

MultiTable: find the single match with the highest confidence for every target attribute

QualTable: find the best matches on a per-table basis

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Context Schema MatchingContext-Sensitive

Experimental Results

“Because of its poor performance, MultiTable is not considered further”

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Conclusion

Current schema matching approaches still have to improve for large and complex schemas.

The large search space increases the likelihood for false matches as well as execution times.

Further difficulties for schema matching are posed by the high expressive power and versatility of modern schema languages like XSD.

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Questions