Chapter 2 Database System Concepts and Architecture Copyright 2011 Pearson Education Inc Publishing as Pearson Addison Wesley Data Models Schemas and Instances Data abstraction Suppression of details of data organization and storage Highlighting of the essential features for an improved understanding of data Copyright 2011 Ramez Elmasri and Shamkant Navathe Data Models Schemas and Instances cont d Data model Collection of concepts that describe the structure of a database Provides means to achieve data abstraction Basic operations Specify retrievals and updates on the database Copyright 2011 Ramez Elmasri and Shamkant Navathe Categories of Data Models High level or conceptual data models Close to the way many users perceive data Low level or physical data models Describe the details of how data is stored on computer storage media Representational data models Easily understood by end users Also similar to how data organized in computer storage Copyright 2011 Ramez Elmasri and Shamkant Navathe Conceptual Data Models Entity Represents a real world object or concept Attribute Represents some property of interest Further describes an entity Relationship among two or more entities Represents an association among the entities Entity Relationship model is a popular high level conceptual data model Copyright 2011 Ramez Elmasri and Shamkant Navathe Representational Data Models Relational data model Used most frequently in traditional commercial DBMSs Object data model New family of higher level implementation data models Closer to conceptual data models Copyright 2011 Ramez Elmasri and Shamkant Navathe Physical Data Models Physical data models Describe how data is stored as files in the computer Access path Structure that makes the search for particular database records efficient Index Example of an access path Allows direct access to data using an index term or a keyword Copyright 2011 Ramez Elmasri and Shamkant Navathe Schemas Instances and Database State Database schema Description of a database Schema diagram A displayed schema Schema construct Each object in the schema Database state or snapshot Data in database at a particular moment in time Copyright 2011 Ramez Elmasri and Shamkant Navathe Schemas Instances and Database State cont d Copyright 2011 Ramez Elmasri and Shamkant Navathe Schemas Instances and Database State cont d Define a new database Specify database schema to the DBMS Initial state Populated or loaded with the initial data Valid state Satisfies the structure and constraints specified in the schema Copyright 2011 Ramez Elmasri and Shamkant Navathe Schemas Instances and Database State cont d Schema evolution Changes applied to schema as application requirements change Copyright 2011 Ramez Elmasri and Shamkant Navathe Three Schema Architecture and Data Independence Internal level Describes physical storage structure of the database Conceptual level Describes structure of the whole database for a community of users External or view level Describes part of the database that a particular user group is interested in Copyright 2011 Ramez Elmasri and Shamkant Navathe Three Schema Architecture and Data Independence cont d Copyright 2011 Ramez Elmasri and Shamkant Navathe Data Independence Capacity to change the schema at one level of a database system Without having to change the schema at the next higher level Types Logical Physical Copyright 2011 Ramez Elmasri and Shamkant Navathe DBMS Languages Data definition language DDL Defines both schemas Storage definition language SDL Specifies the internal schema View definition language VDL Specifies user views mappings to conceptual schema Data manipulation language DML Allows retrieval insertion deletion modification Copyright 2011 Ramez Elmasri and Shamkant Navathe DBMS Interfaces Menu based interfaces for Web clients or browsing Forms based interfaces Natural language interfaces Speech input and output Interfaces for parametric users Interfaces for the DBA Copyright 2011 Ramez Elmasri and Shamkant Navathe The Database System Environment DBMS component modules Buffer management Stored data manager DDL compiler Interactive query interface Query compiler Query optimizer Precompiler Copyright 2011 Ramez Elmasri and Shamkant Navathe The Database System Environment cont d DBMS component modules Runtime database processor System catalog Concurrency control system Backup and recovery system Copyright 2011 Ramez Elmasri and Shamkant Navathe Copyright 2011 Ramez Elmasri and Shamkant Navathe Centralized and Client Server Architectures for DBMSs Centralized DBMSs Architecture All DBMS functionality application program execution and user interface processing carried out on one machine Copyright 2011 Ramez Elmasri and Shamkant Navathe Copyright 2011 Ramez Elmasri and Shamkant Navathe Basic Client Server Architectures Servers with specific functionalities File server Maintains the files of the client machines Printer server Connected to various printers all print requests by the clients are forwarded to this machine Web servers or e mail servers Copyright 2011 Ramez Elmasri and Shamkant Navathe Basic Client Server Architectures cont d Client machines Provide user with Appropriate interfaces to utilize these servers Local processing power to run local applications Copyright 2011 Ramez Elmasri and Shamkant Navathe Copyright 2011 Ramez Elmasri and Shamkant Navathe Basic Client Server Architectures cont d Client User machine that provides user interface capabilities and local processing Server System containing both hardware and software Provides services to the client machines Such as file access printing archiving or database access Copyright 2011 Ramez Elmasri and Shamkant Navathe Two Tier Client Server Architectures for DBMSs Server handles Query and transaction functionality related to SQL processing Client handles User interface programs and application programs Copyright 2011 Ramez Elmasri and Shamkant Navathe Two Tier Client Server Architectures cont d Open Database Connectivity ODBC Provides application programming interface API Allows client side programs to call the DBMS Both client and server machines must have the necessary software installed JDBC Allows Java client programs to access one or more DBMSs through a standard interface Copyright 2011 Ramez Elmasri and Shamkant Navathe Three Tier and n Tier Architectures for Web Applications Application server or Web server Adds intermediate layer between client and the database server
View Full Document
Unlocking...