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Distributed Database Management Systems. Reading. Textbook: Ch. 4. Design Issues. Placing of data and programs (DBMS and application) Network issues. Level of Sharing. No sharing Data sharing Data and program sharing. Heterogeneous environment!. Top-Down Design.

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Presentation Transcript
reading
Reading
  • Textbook: Ch. 4

CSCE 824 - Spring 2011

design issues
Design Issues
  • Placing of data and programs (DBMS and application)
  • Network issues

CSCE 824 - Spring 2011

level of sharing
Level of Sharing
  • No sharing
  • Data sharing
  • Data and program sharing

Heterogeneous environment!

CSCE 824 - Spring 2011

top down design
Top-Down Design
  • Global Conceptual schema  distribution
    • Fragmentation
    • Replication
    • Allocation
  • Figure 3.2

CSCE 824 - Spring 2011

correctness of fragmentation
Correctness of Fragmentation
  • Completeness: FR={R1, …, Rn}
  • Reconstruction: R=Ri, RiR
  • Disjointness:
    • Horizontal: does not  djRisuch that djRkwhere ki
    • Vertical: same as horizontal for non-primary key attributes

1&2: Lossless-join (normalization)

CSCE 824 - Spring 2011

data directory
Data Directory
  • Global vs. local conceptual schemas
    • How to search?
    • Where to store?
    • Single vs. multiple copies?

CSCE 824 - Spring 2011

current research
Current Research
  • Allocation: new requirements, technology, etc.
  • Where to store the fragments?
  • Dynamic environment
    • Usage pattern
    • Application characteristics
    • Network changes
    • Security

CSCE 824 - Spring 2011

bottom up approach
Bottom-Up Approach
  • Multi-database systems
  • How to integrate them into 1 database?
    • Interoperability

CSCE 824 - Spring 2011

database integration
Database Integration
  • Physical integration
    • Materialized database: data warehouses
    • Extract-transform-load (ETL) tools
  • Logical integration
    • Virtual (not materialized) integration
    • Enterprise Information Integration

CSCE 824 - Spring 2011

data warehouses
Data Warehouses
  • On-line Analytical Processing (OLAP) applications:
    • Decision support systems
    • Trend analysis and forecasting
  • Complex queries, large databases
  • Materialized view maintanence

CSCE 824 - Spring 2011

logical integration
Logical Integration
  • No materialized global database
  • Virtual integration: data remains at the local (operational) databases
  • Global conceptual schema may not contain everything from local schemas
  • Autonomous and heterogeneous local systems

CSCE 824 - Spring 2011

bottom up design
Bottom-Up Design
  • Global Conceptual Schema (GCS or mediated schema)
    • Defined first: local conceptual schemas (LCS) are mapped to GCS
    • Defined during the integration of the LCSs and develop the corresponding mappings from LCSs to the GCS

CSCE 824 - Spring 2011

gcs defined first
GCS Defined First
  • Local-as-view (LAV) systems
    • Each LCS is treated as a view over the GCS
    • Query results: constrained to the objects in the local DBs while the GCS definition may be richer
    • Potential incomplete answers
  • Global-as-view GCS is defined as a set of views over the LCSs
    • View definition defines how to derive elements of the GCS
    • Query results: constrained to the GCS while the local DBs might be richer

CSCE 824 - Spring 2011

design tasks
Design Tasks
  • Schema translation
  • Schema generation
  • Figure 4.3

CSCE 824 - Spring 2011

intermediate canonical representation
Intermediate Canonical Representation
  • Expressive to incorporate all concepts in the local databases
  • Simple, intuitive, practical, etc.
  • Example: E/R model, relational model, graph/tree models, etc.
  • Tools

CSCE 824 - Spring 2011

schema generation
Schema Generation
  • Schema matching: syntax and semantics
  • Integration of common schema elements
  • Schema mapping
  • See example 4.1, 4.2

CSCE 824 - Spring 2011

schema matching
Schema Matching
  • Defined or discovered (e.g., web data)
  • Rules:
    • Correspondence between 2 elements
    • Predicate whether the correspondence holds or not
    • Similarity value between the 2 elements

CSCE 824 - Spring 2011

finding correspondence
Finding Correspondence
  • Difficult process due to schema heterogeneity
  • Can be automated?
    • Insufficient schema and instance information
    • Unavailability of schema documentation
    • Subjectivity of matching

CSCE 824 - Spring 2011

matching algorithm issues
Matching Algorithm Issues
  • Schema vs. instance matching
    • Concept match
    • Data instance: semantic inconsistencies
  • Element-level vs. structure-level mapping
    • Element name  semantics
    • Multiple attribute mapping?
  • Matching cardinality
    • One-to-one, one-to-many, many-to-many

CSCE 824 - Spring 2011

semantic schema heterogeneity
Semantic Schema Heterogeneity
  • Semantic: meaning, interpretation, and intended use of data
    • Synonyms, homonyms, hypernyms
    • Different ontologies
    • Imprecise wording

CSCE 824 - Spring 2011

slide22

Structural Schema Heterogeneity

  • Type conflict: attribute vs. entity
  • Dependency conflict: mapping cardinality inconsistencies
  • Key conflict: different primary keys
  • Behavioral conflict: modeling assumptions, e.g., referential integrity, deletion, etc.

Farkas

CSCE 824 - Spring 2011

22

schema integration
Schema Integration
  • Binary
  • N-ary

CSCE 824 - Spring 2011

schema mapping
Schema Mapping
  • How the data from local databases can be mapped to GCS
  • Mapping creating
  • Mapping maintanence

CSCE 824 - Spring 2011

mapping creation
Mapping Creation
  • Input: LCS, GCS, M (schema matches)
  • Output: Q={Q1, …, Qk} such that
    • DBGCS =  Q(DBCLS)

CSCE 824 - Spring 2011

security objectives
Security Objectives
  • Confidentiality
  • Integrity
  • Availability

CSCE 824 - Spring 2011

question 1
Question 1
  • How distributed databases impact the security objectives?
    • Confidentiality in traditional vs. distributed DBs
    • Integrity in traditional vs. distributed DBs
    • Availability in traditional vs. distributed DBs

CSCE 824 - Spring 2011

integrity
Integrity
  • Correctness criteria
    • Top-down design
    • Bottom-up design

CSCE 824 - Spring 2011

availability
Availability
  • What are the issues related to availability when dealing with
    • Top-down design
    • Bottom-up design

CSCE 824 - Spring 2011

confidentiality
Confidentiality
  • (will be covered in 2nd part of semester but…)
  • Centralized vs. distributed security policy
    • Top-down design
    • Bottom-up design

CSCE 824 - Spring 2011

slide31
Next Class

Semantics-based Database Integration

CSCE 824 - Spring 2011

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