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 Data Models and Schemas Data model One fundamental characteristic of the database approach is that it provides some level of data abstraction Collection of concepts that describe the structure of a database 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 4 2 1 1 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 Hides many details of data storage on disk but can be implemented on a computer system directly 5 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 Semantic data model Semantic Web 6 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 7 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 8 Schemas Instances and Database State In any data model it is important to distinguish between the description of the database and the database itself 9 Schemas Instances and Database State Database schema Description of a database Schema diagram Displays selected aspects of schema Schema construct Each object instance in the schema e g STUDENT or COURSE Database state or snapshot Data in database at a particular moment in time 10 Schemas Instances and Database State 11 Schemas Instances and Database State Table Name Relation Name 12 Schemas Instances and Database State Column name Field name 13 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 14 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 16 Three Schema Architecture and Data Independence 17 Three Schema Architecture and Data Independence 18 Three Schema Architecture and Data Independence 19 Three Schema Architecture and Data Independence 20 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 21 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 23 DBMS User Interfaces UIs 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 24 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 26 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 27 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 printing archiving or database access 28 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 29 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 Java Database Connectivity JDBC Allows Java client programs to access one or more DBMSs through a standard interface 30 Three Tier and n Tier Architectures for Web Applications 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 31 Service Oriented Architecture Many different components of a system are services These may reside in the same machine or different machines Database service various business process services calendar service etc 32 Three Tier Architecture 33 2 6 Classification of Database Management
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