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DBMS Chapter 1
DBMS Chapter 1
28
Computer Networking
Post-Graduate
01/19/2015

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Cards

Term

 

 

 

Database

Definition

 

  • Collection of interrelated data
  • Represents a subset of the real world
  • Logically coherent with inherent meaning
  • Intended group of users and applictions
Term

 

 

 

DBMS (Database Management Systems)

Definition

 

 

  • Collection of general-purpose software that allows us to definecreate and manipulate a database.
Term

 

 

 

Database system

Definition

 

 

  • Combination between a database and a DBMS.
Term

 

 

 

File based approach

Definition
  • Only data is stored in a file
  • Structure is defined within the applications
  • Waste of storage due to redundancy
  • Data inconsistency (every changed entry in one file needs to be changed in the other files)
  • Strong data-application dependancy (change in definition = change in all applications)
  • Difficult to integrate various apps (high difficulty and cost)
  • Only one user/application per file
Term

 

 

 

Database-oriented approach

Definition
  • DBMS contains both data and description of database structure
  • The catalog stores all this metadata
  • Changes in the structure just require a catalaog change, program-data independence
  • Subsets of data can be defined
  • Multiple users can access the same data at the same time = concurrency control
Term

 

 

 

Elements of a DB system

Definition
 
  • Data model
  • Schemas and instances
  • Three-schema architecture
  • Catalog (data dictionary)
  • DBMS languages
Term

 

 

 

Data model

Definition

 

 

Collection of concepts that can be used to define the structure of the database

Term

 

 

 

Data models: conceptual

Definition

 

 

  • High-level concepts
  • Representation of part of reality
  • Close to how the user percieves the data
  • (E)ER, OOModels (UML)
Term

 

 

 

Data models: implementation

Definition
  • Concepts that may be understood by end users
  • Not too far removed from physical data organization
  • Some details of data storage are hidden (but can be implemented in a direct way)
  • Hierarchical model, network model, relational model, ODMG model
Term

 

 

 

Data models: physical

Definition
 
 
 
  • Low-level concepts that describe the data physical storage details
Term

 

 

 

Schemas, instances and database state

Definition

 

 

  • Database schema: description of a database, specified during design, not expected to change frequently (= inf. stored in catalog)
  • Database state: the data contained in the database at a particular moment (= current set of instances)
Term

 

 

 

Three-schema Architecture: External/user view

Definition

 

 

  • Each external schema describes the part of the database that a particular group is interested in and hides the rest of the DB
  • High-level data model or an implementation data model can be used
Term

 

 

 

Three-schema Architecture: Conceptual schema

Definition
  • Specifies objects, characteristics of objects, relationships between objects, integrity rules and object behaviour.
  • Hides physical storage details. Concentrates on describing entities, data types, relationships and constraints.
  • A high-level data model or an implementation data model can be used.
Term

 

 

 

 

Three-schema Architecture: Internal schema

Definition
 
 
 
  • Specifies how data is stored/organised physically
  • Acces paths, indexes, etc.
Term

 

 

 

Catalog: data dictionary

Definition

 

  • System database with metadata
  • Contains definition of:
      • Conceptual schema
      • External view/user views
      • Physical schema
Term

 

 

 

 

DBMS Languages: DDL

Definition
 
 
  • Data Definition Language
  • Used by the Database Administrator (DBA)
  • Defines conceptual, internal and physical schemas
Term

 

 

 

 

DBMS Languages: DML

Definition
 
  • Data Manipulation Language
  • Retrieve, insert, delete or modify data
  • Can be entered interactively (terminal) or embedded in a general-purpose programming language
Term

 

 

 

 

Advantages of DB design

Definition

 

  • Data and functional independence
  • Databese modeling
  • Managing data redundancy
  • Specifying integrity rules
  • Data security
  • Backup and recovery facilities
  • Performance utilities
Term

 

 

 

Data independence: physical

Definition

 

 

  • Changes to data storage specifications
      • No need to change applications
      • No need to change conceptual schema
  • DBMS provides interfaces between conceptual and physical data models
  • New acces paths, indices, different storage media
Term

 

 

 

 

Data independence: logical

Definition

 

  •  Changes in the conceptual schema
      • No need to change software applications
  • DBMS provides interfaces between conceptual schema and external views
  • Adding new objects, new characteristics of objects
Term

 

 

 

 

Functional independence

Definition
  • Function
        • Interface (signature): name of the function and its arguments
        • Implementation (method): specifies how the function should be executed
    • Implementation can change without impact on software applications
  • Information hiding
Term

 

 

 

 

Database modeling

Definition

 

  • Data model specifies objects, characteristics of objects, relationships between objects, integrity rules and functions.
  • Should provide formal and perfect mapping of the real world.
  • Hierarchical, CODASYL, (E)ER, relationa, OOModel...
Term

 

 

 

 

Managing data redundancy

Definition
  • Redundant data may be positive
      • Increase in performance
      •            Use of distributed environments

DBMS manages redundancy

  • Synchronization
  • Consistency

Comparison to file-based redundancy

  • Guarantees correctness
  • No user intervention required
  • More efficient
  • Errors unlikely
Term

 

 

 

 

Integrity rules

Definition
  • Determine correctness of data
      • Syntactical errors
      • Semantical errors
  • Integrity rules are stored
      • Embedded in applications (file based aproach to DBManagement)
      • Specified as part of conceptual schema and stored in catalog (database approach)
Term

 

 

 

 

Enforcement of Integrity Rules

Definition

 

  • By applications accessing the files
  • By the DBMS whenever it is updated

 

  • IR can be sensitive to simultaneous usage of data in a distributed environment
Term

 

 

 

 

Data security issues

Definition

 

  • User access can be restricted to diferent levels, reading and writing
  • Data access can be managed via accounts and passwords for users or groups
  • Each personal account has its own authorization rules, stored in the catalog
Term

 

 

 

 

Backup and recovery facilities

Definition
  • Loss of data
          • Hardware or network errors
          • Bugs in system software or applications
  • Backup facilities perform full or incremental backups
          • Restoring the system to a previous state
  • Recovery facilities allow to restore data after loss or damage
          • Recreate the state of the system prior to the failure
Term

 

 

 

 

Performance utilities

Definition
  • Part of the job of the DBA
  • Distributing data storage
  • Tuning indices to allow faster queries
  • Tuning queries to improve performance
  • Optimizing buffer management
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