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Issues In Distributed Data Management

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  1. Issues In Distributed Data Management Heterogeneous Distributed Database - Philip K. Nukpe

  2. Heterogeneous Distributed Database Heterogeneous Distributed Database - Philip K. Nukpe

  3. Definition: ‘Composed of heterogeneous hardware, operating system database management system and applications’ • Provides logically integrated view of existing heterogeneous distributed databases. • The three-level architecture of a Heterogeneous Distributed Database System (HDDMS) User User User User External Schema 1 External Schema 2 External Schema 3 Conceptual Schema Internal Schema Heterogeneous Distributed Database - Philip K. Nukpe

  4. Challenges posed by integrating distributed databases: • Data management system (different vendors) • Data Models (i.e. relational, text indexing, object) • Query the transaction processing algorithms • Data types (i.e., text graphics, multimedia, hypermedia) • Format (i.e. Structured, unstructured) • Semantics Heterogeneous Distributed Database - Philip K. Nukpe

  5. In a heterogeneous database (HDD), the local database is not managed by the same distributed database management system. • Federated Database: “ A combination of autonomous, heterogeneous databases that are operating together” • Co-ordinating software is called Federated DBMS • Component Databases are individual databases that take part in a Federated Database System. • Component databases can continue to execute local tasks while participating in a federation. Heterogeneous Distributed Database - Philip K. Nukpe


  6. Typical Heterogeneous databases include: • World Wide Web • Multimedia • Preservation of the database’s autonomy is paramount. • Data access facilities in Heterogeneous Database Systems can range from: • browsing across component databases • querying a centralised data warehouse • querying multiple databases. • A heterogeneous database system can be provided with a multidatabase query language. Heterogeneous Distributed Database - Philip K. Nukpe

  7. This allows queries to be expressed with direct reference to elements(data) of the component database. • Multidatabase has been classified according to the following criteria: 1. Distribution: Data can be placed in many distributed databases. Databases can be found in the same or different computer systems. 2. Heterogeneity: This is found in the differences in technology i.e., software, hardware, and operating system. Heterogeneous Distributed Database - Philip K. Nukpe

  8. The two types of heterogeneity are those that are due to: - differences in various DBMSs - differences in data semantics 3. Autonomy: A component database can have the following autonomies: • Design Autonomy (Choice of data presentation and attributes) • Communication Autonomy (ability to decide on its own when to communicate with other components of the federated database system.) • Execution Autonomy:( ability to execute some of its operations locally without influence by external operations that are executed in other component databases or in the federation database system) Heterogeneous Distributed Database - Philip K. Nukpe

  9. Component database in a federation although autonomous, allow partial and controlled sharing of their data. • A federated database can be classified into two classes depending on who manages the federation and how the component database are co ordinating: • LOOSELY COUPLED FEDERATED DATABSE SYSTEM • User required to take responsibility of producing and managing the federation. • No control from the federation database or mangers. • Also called InteroperableDatabaseSystem Heterogeneous Distributed Database - Philip K. Nukpe

  10. TIGHTLY COUPLED FEDERATED DATABASE • Federate system and managers produce and manage the federation • Responsible for controlling the component databases. • PROBLEMS IN INTEGRATING HETEROGENEOUS DATABASES • Semantic Heterogeneity (Different Database designers represent the same object in different ways.) e.g. Synonyms - same entity different names Homonyms - different entities same names Heterogeneous Distributed Database - Philip K. Nukpe

  11. Description Heterogeneity(Different characteristics are used to describe the same object) • Model Heterogeneity(use of different models to represent the same data e.g. SSADM, E-R Diagram, Use Cases) REQUIREMENT FOR FDDMS • Provision of a homogeneous interface (federated schema) to overcome heterogeneity) • Autonomy of local databases(CDBS) to be maintained. • Federated schema to maintain definition of external schema. • The support of mechanism to guarantee consistency. Heterogeneous Distributed Database - Philip K. Nukpe

  12. Characteristics of FDB Environment • Due to decentralisation of corporate data, heterogeneous software, hardware are required hence FDBS is the natural choice for such systems. • Fragmentation Transparency • Location Transparency • Local Transparency (Diagram ) Heterogeneous Distributed Database - Philip K. Nukpe

  13. External Schema External Schema External Schema Federated Schema FederatedSchema Export Schema Export Schema Export Schema Component Schema Component Schema Local Schema Local Schema LDBC LDBC Heterogeneous Distributed Database - Philip K. Nukpe

  14. Federated Multidatabase Architecture • Local Schema • Conceptual Schema of a component Database • Component Schema • Translation of local Schema into data model • Export Schema • Subset of component Schema • Include access control Heterogeneous Distributed Database - Philip K. Nukpe

  15. Federated Schema • integrates export Schema & Include information on data distribution • support distribution feature of FDBS • External Schema • Define user/application interface Heterogeneous Distributed Database - Philip K. Nukpe

  16. Common (Canonical)Data Model (CDM) • mapping of a component data model database to the data model of all participating systems in a Multidatabase systems. • Transaction Management • Serialisability • Tickets Heterogeneous Distributed Database - Philip K. Nukpe

  17. Tickets operations • Only global transactions must take ticket values • Local transaction don’t take ticket values • Two Approaches to using Tickets • Optimistic Ticket Method (OTM) • Conservative (pessimistic) Ticket Method (CTM) Heterogeneous Distributed Database - Philip K. Nukpe