CSC 426 Chapter 02, Fall 2011

Chapter 2 Overview of Database Languages and Architectures  Data Models, Schemas, and Instances  The Database System Environment  Centralized and Client/Server Architectures for DBMSs  Classification of Database Management Systems Chapter 2 Outline  Basic client/server DBMS architecture ◦ Client module ◦ Server module Database System Concepts and Architecture  Data abstraction ◦ Suppression of details of data organization and storage ◦ Highlighting of the essential features for an improved understanding of data Data Models, Schemas, and Instances  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 Data Models, Schemas, and Instances (cont'd.)  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 Categories of Data Models (cont'd.)  Relational data model ◦ Used most frequently in traditional commercial DBMSs Categories of Data Models (cont'd.)  Database schema ◦ Description of a database  Schema diagram ◦ Displays selected aspects of schema  Database state or snapshot ◦ Data in database at a particular moment in time Schemas, Instances, and Database State 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 Schemas, Instances, and Database State (cont'd.)  Schema evolution ◦ Changes applied to schema as application requirements change Schemas, Instances, and Database State (cont'd.)  Loading ◦ Load existing data files  Backup ◦ Creates a backup copy of the database Database System Utilities  Database storage reorganization ◦ Reorganize a set of database files into different file organizations  Performance monitoring ◦ Monitors database usage and provides statistics to the DBA Database System Utilities (cont'd.)  Centralized DBMSs Architecture ◦ All DBMS functionality, application program execution, and user interface processing carried out on one machine Centralized and Client/Server Architectures for DBMSs  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 Basic Client/Server Architectures  Client machines ◦ Provide user with: • Appropriate interfaces to utilize these servers • Local processing power to run local applications 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 Basic Client/Server Architectures (cont'd.)  Server handles ◦ Query and transaction functionality related to SQL processing  Client handles ◦ User interface programs and application programs Two-Tier Client/Server Architectures for DBMSs  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 Two-Tier Client/Server Architectures (cont'd.)  Application server or Web server ◦ Adds intermediate layer between client and the database server ◦ Runs application programs and stores business rules  N-tier ◦ Divide the layers between the user and the stored data further into finer components Three-Tier and n-Tier Architectures for Web Applications  Data model • Relational • Object • Hierarchical and network (legacy) • Native XML DBMS  Number of users • Single-user • Multiuser Classification of Database Management Systems  Number of sites • Centralized • Distributed • Homogeneous • Heterogeneous  Cost • Open source • Different types of licensing Classification of Database Management Systems (cont'd.)  Concepts used in database systems  Main categories of data models  Interfaces provided by the DBMS  DBMS classification criteria: ◦ Data model, number of users, number of sties, access paths, cost Summary