csce824-lecture6

csce824-lecture6 - Distributed Database Distributed...

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Unformatted text preview: Distributed Database Distributed Database Management Systems Reading Reading Farkas Textbook: Ch. 4 For next class: Ch. 10.1, 10.2 CSCE 824 ­ Spring 2011 2 Design Issues Design Issues Farkas Placing of data and programs (DBMS and application) Network issues CSCE 824 ­ Spring 2011 3 Level of Sharing Level of Sharing No sharing Data sharing Data and program sharing Heterogeneous environment! Farkas CSCE 824 ­ Spring 2011 4 Top­Down Design Top­Down Design Global Conceptual schema distribution – – – Farkas Fragmentation Replication Allocation Figure 3.2 CSCE 824 ­ Spring 2011 5 Correctness of Correctness of Fragmentation 1. Completeness: FR={R1, …, Rn} 2. Reconstruction: R=∇ Ri, ∀Ri∈R 1&2: Lossless­join (normalization) 3. Disjointness: – – Farkas Horizontal: does not ∃ dj∈Ri such that dj∈Rk where k≠ i Vertical: same as horizontal for non­primary key attributes CSCE 824 ­ Spring 2011 6 Data Directory Data Directory Global vs. local conceptual schemas – How to search? – Where to store? – Single vs. multiple copies? Farkas CSCE 824 ­ Spring 2011 7 Current Research Current Research Farkas Allocation: new requirements, technology, etc. Where to store the fragments? Dynamic environment – – – – Usage pattern Application characteristics Network changes Security CSCE 824 ­ Spring 2011 8 Bottom­Up Approach Bottom­Up Approach Multi­database systems How to integrate them into 1 database? – Interoperability Farkas CSCE 824 ­ Spring 2011 9 Database Integration Database Integration Physical integration – Materialized database: data warehouses – Extract­transform­load (ETL) tools Logical integration – Virtual (not materialized) integration – Enterprise Information Integration Farkas CSCE 824 ­ Spring 2011 10 Data Warehouses Data Warehouses On­line Analytical Processing (OLAP) applications: – – Farkas Decision support systems Trend analysis and forecasting Complex queries, large databases Materialized view maintanence CSCE 824 ­ Spring 2011 11 Logical Integration Logical Integration Farkas 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 12 Bottom­Up Design Bottom­Up 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 Farkas CSCE 824 ­ Spring 2011 13 GCS Defined First GCS Defined First Local­as­view (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 Global­as­viewGCS 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 Farkas CSCE 824 ­ Spring 2011 14 Design Tasks Design Tasks Farkas Schema translation Schema generation Figure 4.3 CSCE 824 ­ Spring 2011 15 Intermediate Canonical Intermediate Canonical Representation Farkas 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 16 Schema Generation Schema Generation Farkas Schema matching: syntax and semantics Integration of common schema elements Schema mapping See example 4.1, 4.2 CSCE 824 ­ Spring 2011 17 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 – – Farkas CSCE 824 ­ Spring 2011 18 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 Farkas CSCE 824 ­ Spring 2011 19 Matching Algorithm Issues Matching Algorithm Issues Farkas Schema vs. instance matching – Concept match – Data instance: semantic inconsistencies Element­level vs. structure­level mapping – Element name semantics – Multiple attribute mapping? Matching cardinality – One­to­one, one­to­many, many­to­many CSCE 824 ­ Spring 2011 20 Semantic Schema Semantic Schema Heterogeneity Farkas Semantic: meaning, interpretation, and intended use of data – Synonyms, homonyms, hypernyms – Different ontologies – Imprecise wording CSCE 824 ­ Spring 2011 21 Structural Schema 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 Farkas Binary N­ary CSCE 824 ­ Spring 2011 23 Schema Mapping Schema Mapping Farkas How the data from local databases can be mapped to GCS Mapping creating Mapping maintanence CSCE 824 ­ Spring 2011 24 Mapping Creation Mapping Creation Input: LCS, GCS, M (schema matches) Output: Q={Q1, …, Qk} such that – DBGCS = ∪ Q(DBCLS) Farkas CSCE 824 ­ Spring 2011 25 Security Objectives Security Objectives Farkas Confidentiality Integrity Availability CSCE 824 ­ Spring 2011 26 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 Farkas CSCE 824 ­ Spring 2011 27 Integrity Integrity Correctness criteria – Top­down design – Bottom­up design Farkas CSCE 824 ­ Spring 2011 28 Availability Availability What are the issues related to availability when dealing with – – Farkas Top­down design Bottom­up design CSCE 824 ­ Spring 2011 29 Confidentiality Confidentiality (will be covered in 2nd part of semester but…) Centralized vs. distributed security policy – Top­down design – Bottom­up design Farkas CSCE 824 ­ Spring 2011 30 Next Class Database Integration Chapter 10 Farkas Farkas CSCE 824 ­ Spring 2011 31 ...
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