Database system concepts and architecture

Database system concepts and architecture

• 1.
  DATABASE SYSTEM CONCEPTSAND ARCHITECTURE Chapter 2
• 2.
  Contents Data Models, Schemas,and Instances Categories of Data Models Schemas, Instances, and Database State Three Schema Architecture and Data Independence Database languages DBMS Interfaces The Database System Environment
• 3.
  Data Model, Schemasand Instances The data model is a collection of concepts that can be used to describe the structure of a database, provides necessary means to achieve this abstraction. By structure of a database we mean data types, relationships, and constraints that hold a database.
• 4.
  Categories of DataModel  High-level or conceptual data model  Provide concepts that are close to the way many users perceive data.  Low level or physical data model  Provides concepts that describe the details of how data is stored in the computer  Representational or implementational data model  Provide concepts that may be understood by user , but that are not too far removed from the way data is organized within the computer.
• 5.
  Schemas,Instances and databaseState  It is important to distinguish between the description of the database and the database itself.  The description of a database is called the database schema which is specified during database design and is not expected to change frequently  The actual data in a database may change quite frequently and is called a database state or snapshot.
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  3Schema Architecture
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  3 Schema Architecture Internal Level has internal schema, which describes the physical storage structure of the database.  Conceptual Level has conceptual schema, and hides the physical storage structures and concentrates on describing entities, data types, relationships , user operations and constraints.  External or View Level describes a part of the database that is particular to a group of users interest in it and hides the rest of the database from that user group.
• 8.
  Data Independence Logical DataIndependence Capacity to change the conceptual schema without changing the application programs or external schema. Physical data independence Capacity to change the internal schema without changing the conceptual schema
• 9.
  DBMS Languages  DDL Used by DBA and Database designers to define both conceptual and internal schemas.  Storage Definition Language (sdl): used to define the internal schema  View Definition Language(VDL): used to specify the user views and their mapping to the conceptual schema.  DML( data manipulation language): for retrieval , insertion,deletion and modification of the data.
• 10.
  Interfaces Menu based Interfaces Forms-basedInterfaces Graphical User Interfaces Natural Language Interfaces Interfaces for Parametric Users Interfaces for DBA
• 11.
  The Database SystemEnvironment
• 12.
  Classification of Database ManagementSystem Several criteria are normally used to classify DBMS’s Data Model Number of Users Number of Sites Cost