DISTRIBUTED DBMS Database:- Logical interrelated collection of shared data, along with description of data, physically distributed over a computer network. DBMS:- The software system that permits the management of the distributed database and makes the distribution transparent to users
CONCEPTSTWO types of Applications• Local application : Application that do not requireddata from other sites.• Global application : Application that required datafrom other sites.
CONCEPTSCharacteristics DDBMS• A collection of logically related shared data.• Data is split into a number of fragments.• Fragments are replicated.•Fragments/ replicas are allocated to sites.
CONCEPTSCharacteristics Of DDBMS• Sites are linked by a communication network.• Data at each site is in the control of a DBMS.•DBMS at each site can handle local applications• Each DBMS participates in at least one globalapplication
ConceptsProperties of DDBMS• Distributed Data Independence : Users shouldnot have to know where data is located (extendsPhysical and Logical Data Independenceprinciples).•Distributed Transaction Atomicity : Users shouldbe able to write Xacts accessing multiple sites justlike local Xacts.
DISTRIBUTED PROCESSINGT T T T T T COM 1 COM 2 Communication Network DB T T T COM 3
ADVANTAGES•Reflects organizational structure•Improved shareability and local autonomy•Improved availability•Improved reliability•Improved performance•Economics•Modular growth
DISADVANTAGES•Complexity•Cost•Security•Integrity control more difficult•Lack of standards•Lack of experience•Database design more complex
Reference Architecture for DDBMS Due to diversity, no accepted architecture equivalent to ANSI/SPARC 3-level architecture. A reference architecture consists of: ◦ Set of global external schemas. ◦ Global conceptual schema (GCS). ◦ Fragmentation schema and allocation schema. ◦ Set of schemas for each local DBMS conforming to 3-level ANSI/SPARC . Some levels may be missing, depending on levels of transparency supported. Can be homogeneous or heterogeneous
TYPE OF DDBMS• Homogeneous DDBMS• All sites use same DBMS product.• Heterogeneous DDBMS• All sites use different DBMS product.
COMPONENET ARCHITECTUREFOR DDBMS• Local DBMS• Data Communication Component• Global System Catalog• Distributed DBMS component
DISTRIBUTED DATABASE DESIGNAND TECHNIQUE• Fragmentation: that are used to break up the database into logical units,called fragments.• Replication: which permits certain data to be stored in more than one site.• Allocation: process of allocating fragments or replicas of fragments for storage at the various site.
TYPES OF FRAGMENTATION• Horizontal fragment of a relation is a subset of the tuples in that relation.• Vertical fragment of a relation keeps only certain attributes of a relation.• Mixed – both horizontal and vertical.• Derived – natural join first to get additionalinformation required then fragment.• Must be able to reconstruct original table.• Can query and update through fragment.
FRAGMENTATION• Strategize to achieve: • Locality of Reference • Improved Reliability and Availability • Improved Performance • Balanced Storage Capacities and Costs • Minimal Communication Costs.• Quantitative and quantitative information• Correctness of Fragmentation • Completeness • Reconstruction • Disjointness.
REPLICATION• Storing data at multiple sites• Example – Internet grocer with multiple warehouses.• CUSTOMER (Cust#, Addr, Location) • Customer info at central location • Location is warehouse that makes deliveries• Where do we store tables?• Fragment?• Replicate?
TRANSPERENCIES IN DDBMS• Transparencies hide implementation details from the user• Example in Centralized databases : Data independence• Main types of transparencies in• DDBMS:Distributed Transparency• Transaction Transparency
DISTRIBUTED TRANSPARENCYAllows the user to see the database as asingle, logical entity.If this transparency is exhibited then theuser does not need to know that1. The data are partitioned.2. Data can be replicated at several sites.3. Data location.
FRAGMENTATIONTRANSPERANCYIf it is provided then the user does not needto know the data is fragmented.Example:SELECT fName, lNameFROM StaffWHERE position = ‘ Manager ’
TRANSACTION TRANSPARENCY• It maintains distributed database’s integrity and consistency.
PARALLEL DBMSA DBMS running across multiple processorsand disks that has been designed to executeoperations in parallel, whenever possible, inorder to improve performance.
Date’s 12 Rules for a DDBMSFundamental PrincipleTo the user, a distributed system should look exactly like a non distributed system.1. Local Autonomy2. No Reliance on a Central Site3. Continuous Operation4. Location Independence5. Fragmentation Independence6. Replication Independence
Date’s 12 Rules for a DDBMS7. Distributed Query Processing8. Distributed Transaction Processing9. Hardware Independence10. Operating System Independence11. Network Independence12. Database Independence Last four rules are ideals.