PowerPoint PresentationChapter 2Data ModelsCategories of data modelsHistory of Data ModelsHistory of Data ModelsHierarchical ModelNetwork ModelSchemas versus InstancesDatabase Schema Vs. Database StateThree-Schema ArchitectureSlide 12Slide 13Data IndependenceSlide 15DBMS LanguagesSlide 17Slide 18DBMS InterfacesOther DBMS InterfacesDatabase System UtilitiesOther ToolsCentralized and Client-Server ArchitecturesBasic Client-Server ArchitecturesSpecialized Servers with Specialized functions:Clients:DBMS ServerTwo Tier Client-Server ArchitectureSlide 29Three Tier Client-Server ArchitectureClassification of DBMSsSlide 32Variations of Distributed Environments:Copyright © 2004 Pearson Education, Inc.Copyright © 2004 Pearson Education, Inc.Chapter 2Database System Concepts and ArchitectureSlide 2-3Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. Data ModelsData Model: A set of concepts to describe the structure of a database, and certain constraints that the database should obey.Data Model Operations: Operations for specifying database retrievals and updates by referring to the concepts of the data model. Operations on the data model may include basic operations and user-defined operations.Slide 2-4Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. Categories of data modelsConceptual (high-level, semantic) data models: Provide concepts that are close to the way many users perceive data. (Also called entity-based or object-based data models.)Physical (low-level, internal) data models: Provide concepts that describe details of how data is stored in the computer.Implementation (representational) data models: Provide concepts that fall between the above two, balancing user views with some computer storage details.Slide 2-5Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. History of Data Models Relational Model: proposed in 1970 by E.F. Codd (IBM), first commercial system in 1981-82. Now in several commercial products (DB2, ORACLE, SQL Server, SYBASE, INFORMIX). Network Model: the first one to be implemented by Honeywell in 1964-65 (IDS System). Adopted heavily due to the support by CODASYL (CODASYL - DBTG report of 1971). Later implemented in a large variety of systems - IDMS (Cullinet - now CA), DMS 1100 (Unisys), IMAGE (H.P.), VAX -DBMS (Digital Equipment Corp.).Hierarchical Data Model: implemented in a joint effort by IBM and North American Rockwell around 1965. Resulted in the IMS family of systems. The most popular model. Other system based on this model: System 2k (SAS inc.)Slide 2-6Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. History of Data ModelsObject-oriented Data Model(s): several models have been proposed for implementing in a database system. One set comprises models of persistent O-O Programming Languages such as C++ (e.g., in OBJECTSTORE or VERSANT), and Smalltalk (e.g., in GEMSTONE). Additionally, systems like O2, ORION (at MCC - then ITASCA), IRIS (at H.P.- used in Open OODB). Object-Relational Models: Most Recent Trend. Started with Informix Universal Server. Exemplified in the latest versions of Oracle-10i, DB2, and SQL Server etc. systems.Slide 2-7Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. Hierarchical Model•ADVANTAGES:•Hierarchical Model is simple to construct and operate on•Corresponds to a number of natural hierarchically organized domains - e.g., assemblies in manufacturing, personnel organization in companies •Language is simple; uses constructs like GET, GET UNIQUE, GET NEXT, GET NEXT WITHIN PARENT etc.•DISADVANTAGES:•Navigational and procedural nature of processing•Database is visualized as a linear arrangement of records•Little scope for "query optimization"Slide 2-8Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. Network Model•ADVANTAGES:•Network Model is able to model complex relationships and represents semantics of add/delete on the relationships.•Can handle most situations for modeling using record types and relationship types.•Language is navigational; uses constructs like FIND, FIND member, FIND owner, FIND NEXT within set, GET etc. Programmers can do optimal navigation through the database.•DISADVANTAGES:•Navigational and procedural nature of processing•Database contains a complex array of pointers that thread through a set of records. Little scope for automated "query optimization”Slide 2-9Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. Schemas versus Instances•Database Schema: The description of a database. Includes descriptions of the database structure and the constraints that should hold on the database.•Schema Diagram: A diagrammatic display of (some aspects of) a database schema.•Schema Construct: A component of the schema or an object within the schema, e.g., STUDENT, COURSE.•Database Instance: The actual data stored in a database at a particular moment in time. Also called database state (or occurrence).Slide 2-10Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. Database Schema Vs. Database State•Database State: Refers to the content of a database at a moment in time.•Initial Database State: Refers to the database when it is loaded•Valid State: A state that satisfies the structure and constraints of the database.•Distinction•The database schema changes very infrequently. The database state changes every time the database is updated. •Schema is also called intension, whereas state is called extension.Slide 2-11Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. Three-Schema Architecture•Proposed to support DBMS characteristics of:•Program-data independence.•Support of multiple views of the data.Slide 2-12Elmasri and Navathe, Fundamentals of Database Systems, Fourth EditionCopyright © 2004 Pearson Education, Inc. Three-Schema Architecture•Defines DBMS schemas at three levels:•Internal schema at the internal level to describe physical storage structures and access paths. Typically uses a physical data
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