Chapter 2 Concepts and Architecture CS 6360 Database Systems Chris Irwin Davis Ph D Email cid021000 utdallas edu Phone 972 883 3574 O ce ECSS 4 705 Chapter 2 Outline 2 1 Data Models Schemas and Instances 2 2 Three Schema Architecture and Data Independence 2 3 Database Languages and Interfaces 2 4 The Database System Environment 2 5 Centralized and Client Server Architectures for DBMSs 2 6 Classification of Database Management Systems 2 2 1 Data Models Schemas and Instances Concepts and Architecture Basic client server DBMS architecture Client module Server module 4 Data Models and Schemas Data abstraction Suppression of details of data organization and storage Highlighting of the essential features for an improved understanding of data 5 Data Models and Schemas 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 Dynamic aspect or behavior of a database application Allows the database designer to specify a set of valid operations allowed on database objects 6 Categories of Data Models Implementation 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 Hides many details of data storage on disk but can be implemented on a computer system directly 7 Categories of Data Models Conceptual Types 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 8 Categories of Data Models Conceptual Features 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 9 Categories of Data Models Physical 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 10 Schemas Instances and Database State In any data model it is important to distinguish between the description of the database and the database itself 11 Schemas Instances and Database State Database schema Description of a database Schema diagram Displays selected aspects of schema Schema construct Each object in the schema e g STUDENT or COURSE Database state or snapshot Data in database at a particular moment in time 12 Schemas Instances and Database State 13 Schemas Instances and Database State Table Name Relation Name 14 Schemas Instances and Database State Column name Field name 15 Schemas Instances and Database State Define a new database Populated or loaded with the initial data Valid state Specify database schema to the DBMS Initial state Satisfies the structure and constraints specified in the schema Schema evolution Changes applied to schema as application requirements change 16 2 2 Three Schema Architecture and Data Independence 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 18 Three Schema Architecture and Data Independence 19 Three Schema Architecture and Data Independence 20 Three Schema Architecture and Data Independence 21 Three Schema Architecture and Data Independence 22 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 For example changing to a different DBMS or disk drive without having to change the schema 23 2 3 Database Languages and Interfaces 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 25 DBMS Languages cont d High level or nonprocedural Declarative DML Can be used on its own to specify complex database operations concisely Set at a time or set oriented Low level or procedural DML Must be embedded in a general purpose programming language Record at a time 26 DBMS Interfaces Menu based interfaces for Web clients or browsing Forms based interfaces Graphical user interfaces Like SSMS Natural language interfaces Speech input and output Interfaces for parametric users Interfaces for the DBA 27 2 4 The Database System Environment Database System Utilities Loading Load existing data files Backup Creates a backup copy of the database Database storage reorganization Reorganize a set of database files into different file organizations Performance monitoring Monitors database usage and provides statistics to the DBA 29 The Database System Environment DBMS component modules Buffer management Stored data manager DDL compiler Interactive query interface Query compiler Query optimizer Pre compiler 30 The Database System Environment DBMS component modules Runtime database processor System catalog Concurrency control system Backup and recovery system Backup it s not whether you re paranoid it s whether you re paranoid enough 31 32 2 5 Centralized and Client Server Architectures for DBMSs 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 This was the mainframe model with dumb terminals It is still widely used 34 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 35 Basic Client Server Architectures Client machines Provide user with Appropriate interfaces to utilize these servers Local processing power to run local applications Server System containing both hardware and software Provides services to the client machines Such as file access
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