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Wrapper-Based Evolution of Legacy Information System

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Title: Wrapper-Based Evolution of Legacy Information System


1
Wrapper-Based Evolution of Legacy Information
System
  • Philippe Thiran et al
  • Fcculties University Notre-Dame de la Paix

2
Outline
  • Why Data Wrappers?
  • Building R/W Data Wrappers
  • R/W Wrapper Architecture
  • Generating Data Wrapper

3
Why Data Wrappers?
  • Architectural shifts from centralized to
    distributed and cooperative paradigm
  • Data consistency in legacy architecture
  • Explicit constraints guaranteed legacy system
  • Implicit constraints data consistency is
    guaranteed by client application code
  • Example
  • PR field of record type ORDER refer a definite
    PRODUCT record
  • Implicit constraints to create or modify an
    ORDER, the referred PRODUCT should be first
    checked

ORDER PR
Product
4
Why Data Wrappers?
  • Plug a new application component into such a
    legacy architecture
  • How to validate the implicit data property?
  • Forward Wrappers
  • Translate data and queries from the legacy data
    model
  • Take charge of the validation logic

5
Why Data Wrappers?
  • Reuse a legacy component in a modern system
  • Semantic mismatch many important constraints and
    structures are ignored by data management system
  • Backward Wrappers
  • Query and update the new data
  • Data integrity is ensured by both the new and
    legacy app

6
What is a Data Wrapper?
  • Component inserted between the legacy database
    and the application component to
  • Extend the lifetime of existing system
  • Address the heterogeneity by providing a standard
    and common interface
  • Allows to transparently incorporate new
    capabilities
  • Provides a smooth path to a step-by-step
    modernization of a complex legacy system
  • Interface of a Data Wrapper
  • A wrapper schema
  • A common query language

7
Outline
  • Why Data Wrappers?
  • Building R/W Data Wrappers
  • R/W Wrapper Architecture
  • Generating Data Wrapper

8
Bridge the Semantic Gap
  • Data Wrapper a new application component that
    query and update the contents of a legacy
    database
  • Physical schema explicit structures and
    constraints
  • Logical schema explicit and implicit structures,
    accessed by the wrapper
  • By accessing the logical schema, data wrappers
    address the implicit constraints
  • Reject the updates that violate the implicit
    constraints

9
Building R/W Wrapper
  • Wrapper Schema Definition
  • Recover explicit constraints
  • Enriched with implicit constraints by reverse
    engineering techniques
  • Program analysis
  • Data analysis

10
Building R/W Wrapper
  • Mapping definition
  • Transform structures
  • Transform constraints
  • Example of update statement

11
Outline
  • Why Data Wrappers?
  • Building R/W Data Wrappers
  • R/W Wrapper Architecture
  • Generating Data Wrapper

12
R/W Wrapper Architecture
  • Query/update analysis
  • Error reporting
  • Query/update and data translation
  • Implicit constraint control
  • Security
  • Concurrency and transaction management

13
Specification of a Wrapper
  • GER a wide spectrum entity-relationship model
  • Generate sub-models
  • Retain necessary parts in the sub-model
  • Rename the constructs
  • Assemble the valid parts
  • Advantage
  • All inter-model transformations equal to
    intra-model process
  • A limit set of primitive operators is sufficient
    to model most database engineering processes
  • Enriched Model
  • Encompass the physical, logical and conceptual
    models
  • Define a set of constructs comprising the
    structures and constraints

14
Model and Schema Specification
  • Constructs entity types, attribute, relationship
    types
  • Built-in Constraints

15
Transformational Mapping Spec
  • Transform a schema from one model to another,
    requiring specific operators
  • Inverse transformation
  • T2(T1(C))C
  • Transformation sequence
  • S1-to-S2(T1 T2 ... Tn) S2T2(T1(S1))
  • S2-to-S1(Tn-1 T2-1 T1-1) S1S2-to-S1(S2)
  • Transformation categories
  • T augment the semantics of the schema
  • T Preserve the semantics of the schema
  • T- Reduce the semantics of the schema
  • Implicit constraints and schema Interpretation

16
Outline
  • Why Data Wrappers?
  • Building R/W Data Wrappers
  • R/W Wrapper Architecture
  • Generating Data Wrapper

17
Generating Wrapper
  • Database reverse engineering
  • Yield all the necessary information to specify
    and develop a wrapper
  • Semi-hardcoded wrapper
  • A model layer and a database layer
  • Schema transformation-based wrapper generation
  • T is used to specify the implicit constraint
    assertions instead of T
  • Operational CASE support
  • Schema processing, mapping processing, and
    wrapper generation

18
Database Reverse Engineering
  • Results
  • Wrapper schema
  • Schema transformation sequence
  • Process
  • Physical extraction
  • Logical extraction
  • Wrapper schema derivation
  • Mapping definition

19
Wrapper Generation
20
Wrapper Generation
  • The results from DBRE
  • Legacy physical schema
  • Legacy logical schema
  • Wrapper schema
  • LS-to-PS mapping is formally defined, used to
    code the implicit constraint control component
  • Structural part of WS-to-LS is used to code the
    query/update translator
  • Instance part of ls-to-ws define the data
    translator

21
Reference
  • Thiran, P. et al, Wrapper-Based Evoluation of
    Legacy Information System, ACM Tran Software
    Engineering and Methodology Vol.15 No.4, October
    2006
  • Brodie, M. et al. 1995. Migrating Legacy Systems,
    Morgan Kaufmann
  • Haninaut, J. et al, 2005, Transformation-Based
    Database Engineering, IDEA Group

22
  • Thanks
  • Questions?
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