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Chapter 12. Distributed Database Management Systems Database Systems: Design, Implementation, and Management, Seventh Edition, Rob and Coronel. In this chapter, you will learn:. What a distributed database management system (DDBMS) is and what its components are

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chapter 12

Chapter 12

Distributed Database Management Systems

Database Systems: Design, Implementation, and Management, Seventh Edition, Rob and Coronel

in this chapter you will learn
In this chapter, you will learn:
  • What a distributed database management system (DDBMS) is and what its components are
  • How database implementation is affected by different levels of data and process distribution
  • How transactions are managed in a distributed database environment
  • How database design is affected by the distributed database environment

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

the evolution of distributed database management systems
The Evolution of Distributed Database Management Systems
  • Distributed database management system (DDBMS)
    • Governs storage and processing of logically related data over interconnected computer systems in which both data and processing functions are distributed among several sites

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

the evolution of distributed database management systems continued
The Evolution of Distributed Database Management Systems (continued)
  • Centralized database required that corporate data be stored in a single central site
  • Dynamic business environment and centralized database’s shortcomings spawned a demand for applications based on data access from different sources at multiple locations

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

the evolution of distributed database management systems continued1
The Evolution of Distributed Database Management Systems (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms advantages and disadvantages
DDBMS Advantages and Disadvantages
  • Advantages include:
    • Data are located near “greatest demand” site
    • Faster data access
    • Faster data processing
    • Growth facilitation
    • Improved communications

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms advantages and disadvantages continued
DDBMS Advantages and Disadvantages (continued)
  • Advantages include (continued):
    • Reduced operating costs
    • User-friendly interface
    • Less danger of a single-point failure
    • Processor independence

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms advantages and disadvantages continued1
DDBMS Advantages and Disadvantages (continued)
  • Disadvantages include:
    • Complexity of management and control
    • Security
    • Lack of standards
    • Increased storage requirements
    • Increased training cost

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms advantages and disadvantages continued2
DDBMS Advantages and Disadvantages (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms advantages and disadvantages continued3
DDBMS Advantages and Disadvantages (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms advantages and disadvantages continued4
DDBMS Advantages and Disadvantages (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

characteristics of distributed management systems
Characteristics of Distributed Management Systems
  • Application interface
  • Validation
  • Transformation
  • Query optimization
  • Mapping
  • I/O interface

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

characteristics of distributed management systems continued
Characteristics of Distributed Management Systems (continued)
  • Formatting
  • Security
  • Backup and recovery
  • DB administration
  • Concurrency control
  • Transaction management

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

characteristics of distributed management systems continued1
Characteristics of Distributed Management Systems (continued)
  • Must perform all the functions of centralized DBMS
  • Must handle all necessary functions imposed by distribution of data and processing
    • Must perform these additional functions transparently to the end user

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

characteristics of distributed management systems continued2
Characteristics of Distributed Management Systems (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms components
DDBMS Components
  • Must include (at least) the following components:
    • Computer workstations
    • Network hardware and software
    • Communications media
    • Transaction processor (application processor, transaction manager)
      • Software component found in each computer that requests data

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms components continued
DDBMS Components (continued)
  • Must include (at least) the following components (continued):
    • Data processor or data manager
      • Software component residing on each computer that stores and retrieves data located at the site
      • May be a centralized DBMS

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

ddbms components continued1
DDBMS Components (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

levels of data and process distribution
Levels of Data and Process Distribution

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

single site processing single site data spsd
Single-Site Processing, Single-Site Data (SPSD)
  • All processing is done on single CPU or host computer (mainframe, midrange, or PC)
  • All data are stored on host computer’s local disk
  • Processing cannot be done on end user’s side of system

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

single site processing single site data spsd continued
Single-Site Processing, Single-Site Data (SPSD) (continued)
  • Typical of most mainframe and midrange computer DBMSs
  • DBMS is located on host computer, which is accessed by dumb terminals connected to it
  • Also typical of first generation of single-user microcomputer databases

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

single site processing single site data spsd continued1
Single-Site Processing, Single-Site Data (SPSD) (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

multiple site processing single site data mpsd
Multiple-Site Processing, Single-Site Data (MPSD)
  • Multiple processes run on different computers sharing single data repository
  • MPSD scenario requires network file server running conventional applications that are accessed through LAN
  • Many multiuser accounting applications, running under personal computer network, fit such a description

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

multiple site processing single site data mpsd continued
Multiple-Site Processing, Single-Site Data (MPSD) (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

multiple site processing multiple site data mpmd
Multiple-Site Processing, Multiple-Site Data (MPMD)
  • Fully distributed database management system with support for multiple data processors and transaction processors at multiple sites
  • Classified as either homogeneous or heterogeneous
  • Homogeneous DDBMSs
    • Integrate only one type of centralized DBMS over a network

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

multiple site processing multiple site data mpmd continued
Multiple-Site Processing, Multiple-Site Data (MPMD) (continued)
  • Heterogeneous DDBMSs
    • Integrate different types of centralized DBMSs over a network
  • Fully heterogeneous DDBMS
    • Support different DBMSs that may even support different data models (relational, hierarchical, or network) running under different computer systems, such as mainframes and microcomputers

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

multiple site processing multiple site data mpmd continued1
Multiple-Site Processing, Multiple-Site Data (MPMD) (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed database transparency features
Distributed Database Transparency Features
  • Allow end user to feel like database’s only user
  • Features include:
    • Distribution transparency
    • Transaction transparency
    • Failure transparency
    • Performance transparency
    • Heterogeneity transparency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distribution transparency
Distribution Transparency
  • Allows management of physically dispersed database as though it were a centralized database
  • Following three levels of distribution transparency are recognized:
    • Fragmentation transparency
    • Location transparency
    • Local mapping transparency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distribution transparency continued
Distribution Transparency (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distribution transparency continued1
Distribution Transparency (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

transaction transparency
Transaction Transparency
  • Ensures database transactions will maintain distributed database’s integrity and consistency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed requests and distributed transactions
Distributed Requests and Distributed Transactions
  • Distributed transaction
    • Can update or request data from several different remote sites on network
  • Remote request
    • Lets single SQL statement access data to be processed by single remote database processor
  • Remote transaction
    • Accesses data at single remote site

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed requests and distributed transactions continued
Distributed Requests and Distributed Transactions (continued)
  • Distributed transaction
    • Allows transaction to reference several different (local or remote) DP sites
  • Distributed request
    • Lets single SQL statement reference data located at several different local or remote DP sites

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed requests and distributed transactions continued1
Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed requests and distributed transactions continued2
Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed requests and distributed transactions continued3
Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed requests and distributed transactions continued4
Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed requests and distributed transactions continued5
Distributed Requests and Distributed Transactions (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed concurrency control
Distributed Concurrency Control
  • Multisite, multiple-process operations are much more likely to create data inconsistencies and deadlocked transactions than are single-site systems

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed concurrency control continued
Distributed Concurrency Control (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

two phase commit protocol
Two-Phase Commit Protocol
  • Distributed databases make it possible for transaction to access data at several sites
  • Final COMMIT must not be issued until all sites have committed their parts of transaction
  • Two-phase commit protocol requires each individual DP’s transaction log entry be written before database fragment is actually updated

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

performance transparency and query optimization
Performance Transparency and Query Optimization
  • Objective of query optimization routine is to minimize total cost associated with execution of request
  • Costs associated with request are function of:
    • Access time (I/O) cost
    • Communication cost
    • CPU time cost
  • Must provide distribution transparency as well as replica transparency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

performance transparency and query optimization continued
Performance Transparency and Query Optimization (continued)
  • Replica transparency
    • DDBMS’s ability to hide existence of multiple copies of data from user
  • Query optimization techniques include:
    • Manual or automatic
    • Static or dynamic
    • Statistically based or rule-based algorithms

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

distributed database design
Distributed Database Design
  • Data fragmentation
    • How to partition database into fragments
  • Data replication
    • Which fragments to replicate
  • Data allocation
    • Where to locate those fragments and replicas

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation
Data Fragmentation
  • Breaks single object into two or more segments or fragments
  • Each fragment can be stored at any site over computer network
  • Information about data fragmentation is stored in distributed data catalog (DDC), from which it is accessed by TP to process user requests

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation continued
Data Fragmentation (continued)
  • Strategies
    • Horizontal fragmentation
      • Division of a relation into subsets (fragments) of tuples (rows)
    • Vertical fragmentation
      • Division of a relation into attribute (column) subsets
    • Mixed fragmentation
      • Combination of horizontal and vertical strategies

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation continued1
Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation continued2
Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation continued3
Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation continued4
Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation continued5
Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation continued6
Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data fragmentation continued7
Data Fragmentation (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data replication
Data Replication
  • Storage of data copies at multiple sites served by computer network
  • Fragment copies can be stored at several sites to serve specific information requirements
    • Can enhance data availability and response time
    • Can help to reduce communication and total query costs

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data replication continued
Data Replication (continued)

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data replication continued1
Data Replication (continued)
  • Replication scenarios
    • Fully replicated database
      • Stores multiple copies of each database fragment at multiple sites
      • Can be impractical due to amount of overhead
    • Partially replicated database
      • Stores multiple copies of some database fragments at multiple sites
      • Most DDBMSs are able to handle the partially replicated database well

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data replication continued2
Data Replication (continued)
  • Replication scenarios (continued)
    • Unreplicated database
      • Stores each database fragment at single site
      • No duplicate database fragments

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data allocation
Data Allocation
  • Deciding where to locate data
  • Allocation strategies
    • Centralized data allocation
      • Entire database is stored at one site
    • Partitioned data allocation
      • Database is divided into several disjointed parts (fragments) and stored at several sites

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

data allocation continued
Data Allocation (continued)
  • Allocation strategies (continued)
    • Replicated data allocation
      • Copies of one or more database fragments are stored at several sites
  • Data distribution over computer network is achieved through data partition, data replication, or combination of both

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

client server vs ddbms
Client/Server vs. DDBMS
  • Way in which computers interact to form system
  • Features user of resources, or client, and provider of resources, or server
  • Can be used to implement a DBMS in which client is the TP and server is the DP

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

client server vs ddbms continued
Client/Server vs. DDBMS (continued)
  • Client/server advantages
    • Less expensive than alternate minicomputer or mainframe solutions
    • Allow end user to use microcomputer’s GUI, thereby improving functionality and simplicity
    • More people in job market have PC skills than mainframe skills
    • PC is well established in workplace

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

client server vs ddbms continued1
Client/Server vs. DDBMS (continued)
  • Client/server advantages (continued)
    • Numerous data analysis and query tools exist to facilitate interaction with DBMSs available in PC market
    • Considerable cost advantage to offloading applications development from mainframe to powerful PCs

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

client server vs ddbms continued2
Client/Server vs. DDBMS (continued)
  • Client/server disadvantages
    • Creates more complex environment
      • Different platforms (LANs, operating systems, and so on) are often difficult to manage
    • An increase in number of users and processing sites often paves the way for security problems

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

client server vs ddbms continued3
Client/Server vs. DDBMS (continued)
  • Client/server disadvantages (continued)
    • Possible to spread data access to much wider circle of users
      • Increases demand for people with broad knowledge of computers and software
      • Increases burden of training and cost of maintaining the environment

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

c j date s twelve commandments for distributed databases
C. J. Date’s Twelve Commandments for Distributed Databases
  • Local site independence
  • Central site independence
  • Failure independence
  • Location transparency
  • Fragmentation transparency
  • Replication transparency

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

c j date s twelve commandments for distributed databases continued
C. J. Date’s Twelve Commandments for Distributed Databases (continued)
  • Distributed query processing
  • Distributed transaction processing
  • Hardware independence
  • Operating system independence
  • Network independence
  • Database independence

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

summary
Summary
  • Distributed database stores logically related data in two or more physically independent sites connected via computer network
  • Distributed processing is division of logical database processing among two or more network nodes
  • Distributed databases require distributed processing
  • Main components of DDBMS are transaction processor and data processor

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

summary continued
Summary (continued)
  • Current database systems can be classified by extent to which they support processing and data distribution
  • Homogeneous distributed database system integrates only one particular type of DBMS over computer network
  • Heterogeneous distributed database system integrates several different types of DBMSs over computer network

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

summary continued1
Summary (continued)
  • DDBMS characteristics are best described as set of transparencies
  • Transaction is formed by one or more database requests
  • Distributed concurrency control is required in network of distributed databases
  • Distributed DBMS evaluates every data request to find optimum access path in distributed database

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

summary continued2
Summary (continued)
  • The design of distributed database must consider fragmentation and replication of data
  • Database can be replicated over several different sites on computer network
  • Client/server architecture refers to way in which two computers interact over computer network to form a system

Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

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