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Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 1
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Chapter 2 Database System Concepts and Architecture
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 3 Outline  Data Models and Their Categories  History of Data Models  Schemas, Instances, and States  Three-Schema Architecture  Data Independence  DBMS Languages and Interfaces  Database System Utilities and Tools  Centralized and Client-Server Architectures  Classification of DBMSs
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 4 Data Models  Data Model:  A set of concepts to describe the structure of a database, the operations for manipulating these structures, and certain constraints that the database should obey.  Data Model Structure and Constraints:  Constructs are used to define the database structure  Constructs typically include elements (and their data types) as well as groups of elements (e.g. entity, record, table), and relationships among such groups  Constraints specify some restrictions on valid data; these constraints must be enforced at all times
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 5 Data Models (continued)  Data Model Operations:  These operations are used for specifying database retrievals and updates by referring to the constructs of the data model.  Operations on the data model may include basic model operations (e.g. generic insert, delete, update) and user-defined operations (e.g. compute_student_gpa, update_inventory)
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 6 Categories of Data Models  Conceptual (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. These are usually specified in an ad-hoc manner through DBMS design and administration manuals  Implementation (representational) data models:  Provide concepts that fall between the above two, used by many commercial DBMS implementations (e.g. relational data models used in many commercial systems).
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 7 Schemas versus Instances  Database Schema:  The description of a database.  Includes descriptions of the database structure, data types, and the constraints on the database.  Schema Diagram:  An illustrative display of (most aspects of) a database schema.  Schema Construct:  A component of the schema or an object within the schema, e.g., STUDENT, COURSE.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 8 Schemas versus Instances  Database State:  The actual data stored in a database at a particular moment in time. This includes the collection of all the data in the database.  Also called database instance (or occurrence or snapshot).  The term instance is also applied to individual database components, e.g. record instance, table instance, entity instance
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 9 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 state when it is initially loaded into the system.  Valid State:  A state that satisfies the structure and constraints of the database.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 10 Database Schema vs. Database State (continued)  Distinction  The database schema changes very infrequently.  The database state changes every time the database is updated.  Schema is also called intension.  State is also called extension.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 11 Example of a Database Schema
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 12 Example of a database state
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 13 Three-Schema Architecture  Proposed to support DBMS characteristics of:  Program-data independence.  Support of multiple views of the data.  Not explicitly used in commercial DBMS products, but has been useful in explaining database system organization
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 14 Three-Schema Architecture  Defines DBMS schemas at three levels:  Internal schema at the internal level to describe physical storage structures and access paths (e.g indexes).  Typically uses a physical data model.  Conceptual schema at the conceptual level to describe the structure and constraints for the whole database for a community of users.  Uses a conceptual or an implementation data model.  External schemas at the external level to describe the various user views.  Usually uses the same data model as the conceptual schema.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 15 The three-schema architecture
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 16 Three-Schema Architecture  Mappings among schema levels are needed to transform requests and data.  Programs refer to an external schema, and are mapped by the DBMS to the internal schema for execution.  Data extracted from the internal DBMS level is reformatted to match the user’s external view (e.g. formatting the results of an SQL query for display in a Web page)
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 17 Data Independence  Logical Data Independence:  The capacity to change the conceptual schema without having to change the external schemas and their associated application programs.  Physical Data Independence:  The capacity to change the internal schema without having to change the conceptual schema.  For example, the internal schema may be changed when certain file structures are reorganized or new indexes are created to improve database performance
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 18 Data Independence (continued)  When a schema at a lower level is changed, only the mappings between this schema and higher- level schemas need to be changed in a DBMS that fully supports data independence.  The higher-level schemas themselves are unchanged.  Hence, the application programs need not be changed since they refer to the external schemas.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 19 DBMS Languages  Data Definition Language (DDL)  Data Manipulation Language (DML)  High-Level or Non-procedural Languages: These include the relational language SQL  May be used in a standalone way or may be embedded in a programming language  Low Level or Procedural Languages:  These must be embedded in a programming language
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 20 DBMS Languages  Data Definition Language (DDL):  Used by the DBA and database designers to specify the conceptual schema of a database.  In many DBMSs, the DDL is also used to define internal and external schemas (views).  In some DBMSs, separate storage definition language (SDL) and view definition language (VDL) are used to define internal and external schemas.  SDL is typically realized via DBMS commands provided to the DBA and database designers
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 21 DBMS Languages  Data Manipulation Language (DML):  Used to specify database retrievals and updates  DML commands (data sublanguage) can be embedded in a general-purpose programming language (host language), such as COBOL, C, C+ +, or Java.  A library of functions can also be provided to access the DBMS from a programming language  Alternatively, stand-alone DML commands can be applied directly (called a query language).
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 22 Types of DML  High Level or Non-procedural Language:  For example, the SQL relational language  Are “set”-oriented and specify what data to retrieve rather than how to retrieve it.  Also called declarative languages.  Low Level or Procedural Language:  Retrieve data one record-at-a-time;  Constructs such as looping are needed to retrieve multiple records, along with positioning pointers.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 23 DBMS Interfaces  Stand-alone query language interfaces  Example: Entering SQL queries at the DBMS interactive SQL interface (e.g. SQL*Plus in ORACLE)  Programmer interfaces for embedding DML in programming languages  User-friendly interfaces  Menu-based, forms-based, graphics-based, etc.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 24 DBMS Programming Language Interfaces  Programmer interfaces for embedding DML in a programming languages:  Embedded Approach: e.g embedded SQL (for C, C++, etc.), SQLJ (for Java)  Procedure Call Approach: e.g. JDBC for Java, ODBC for other programming languages  Database Programming Language Approach: e.g. ORACLE has PL/SQL, a programming language based on SQL; language incorporates SQL and its data types as integral components
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 25 User-Friendly DBMS Interfaces  Menu-based, popular for browsing on the web  Forms-based, designed for naïve users  Graphics-based  (Point and Click, Drag and Drop, etc.)  Natural language: requests in written English  Combinations of the above:  For example, both menus and forms used extensively in Web database interfaces
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 26 Other DBMS Interfaces  Speech as Input and Output  Web Browser as an interface  Parametric interfaces, e.g., bank tellers using function keys.  Interfaces for the DBA:  Creating user accounts, granting authorizations  Setting system parameters  Changing schemas or access paths
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 27 Database System Utilities  To perform certain functions such as:  Loading data stored in files into a database. Includes data conversion tools.  Backing up the database periodically on tape.  Reorganizing database file structures.  Report generation utilities.  Performance monitoring utilities.  Other functions, such as sorting, user monitoring, data compression, etc.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 28 Other Tools  Data dictionary / repository:  Used to store schema descriptions and other information such as design decisions, application program descriptions, user information, usage standards, etc.  Active data dictionary is accessed by DBMS software and users/DBA.  Passive data dictionary is accessed by users/DBA only.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 29 Other Tools  Application Development Environments and CASE (computer-aided software engineering) tools:  Examples:  PowerBuilder (Sybase)  JBuilder (Borland)  JDeveloper 10G (Oracle)
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 30 Typical DBMS Component Modules
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 31 Centralized and Client-Server DBMS Architectures  Centralized DBMS:  Combines everything into single system including- DBMS software, hardware, application programs, and user interface processing software.  User can still connect through a remote terminal – however, all processing is done at centralized site.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 32 A Physical Centralized Architecture
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 33 Basic 2-tier Client-Server Architectures  Specialized Servers with Specialized functions  Print server  File server  DBMS server  Web server  Email server  Clients can access the specialized servers as needed
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 34 Logical two-tier client server architecture
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 35 Clients  Provide appropriate interfaces through a client software module to access and utilize the various server resources.  Clients may be diskless machines or PCs or Workstations with disks with only the client software installed.  Connected to the servers via some form of a network.  (LAN: local area network, wireless network, etc.)
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 36 DBMS Server  Provides database query and transaction services to the clients  Relational DBMS servers are often called SQL servers, query servers, or transaction servers  Applications running on clients utilize an Application Program Interface (API) to access server databases via standard interface such as:  ODBC: Open Database Connectivity standard  JDBC: for Java programming access  Client and server must install appropriate client module and server module software for ODBC or JDBC  See Chapter 9
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 37 Two Tier Client-Server Architecture  A client program may connect to several DBMSs, sometimes called the data sources.  In general, data sources can be files or other non-DBMS software that manages data.  Other variations of clients are possible: e.g., in some object DBMSs, more functionality is transferred to clients including data dictionary functions, optimization and recovery across multiple servers, etc.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 38 Three Tier Client-Server Architecture  Common for Web applications  Intermediate Layer called Application Server or Web Server:  Stores the web connectivity software and the business logic part of the application used to access the corresponding data from the database server  Acts like a conduit for sending partially processed data between the database server and the client.  Three-tier Architecture Can Enhance Security:  Database server only accessible via middle tier  Clients cannot directly access database server
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 39 Three-tier client-server architecture
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 40 Classification of DBMSs  Based on the data model used  Traditional: Relational, Network, Hierarchical.  Emerging: Object-oriented, Object-relational.  Other classifications  Single-user (typically used with personal computers) vs. multi-user (most DBMSs).  Centralized (uses a single computer with one database) vs. distributed (uses multiple computers, multiple databases)
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 41 Variations of Distributed DBMSs (DDBMSs)  Homogeneous DDBMS  Heterogeneous DDBMS  Federated or Multidatabase Systems  Distributed Database Systems have now come to be known as client-server based database systems because:  They do not support a totally distributed environment, but rather a set of database servers supporting a set of clients.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 42 Cost considerations for DBMSs  Cost Range: from free open-source systems to configurations costing millions of dollars  Examples of free relational DBMSs: MySQL, PostgreSQL, others  Commercial DBMS offer additional specialized modules, e.g. time-series module, spatial data module, document module, XML module  These offer additional specialized functionality when purchased separately  Sometimes called cartridges (e.g., in Oracle) or blades  Different licensing options: site license, maximum number of concurrent users (seat license), single user, etc.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 43 History of Data Models  Network Model  Hierarchical Model  Relational Model  Object-oriented Data Models  Object-Relational Models
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 44 History of Data Models  Network Model:  The first network DBMS was implemented by Honeywell in 1964-65 (IDS System).  Adopted heavily due to the support by CODASYL (Conference on Data Systems Languages) (CODASYL - DBTG report of 1971).  Later implemented in a large variety of systems - IDMS (Cullinet - now Computer Associates), DMS 1100 (Unisys), IMAGE (H.P. (Hewlett-Packard)), VAX -DBMS (Digital Equipment Corp., next COMPAQ, now H.P.).
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 45 Example of Network Model Schema
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 46 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.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 47 Network Model  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”
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 48 History of Data Models  Hierarchical Data Model:  Initially implemented in a joint effort by IBM and North American Rockwell around 1965. Resulted in the IMS family of systems.  IBM’s IMS product had (and still has) a very large customer base worldwide  Hierarchical model was formalized based on the IMS system  Other systems based on this model: System 2k (SAS inc.)
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 49 Hierarchical Model  Advantages:  Simple to construct and operate  Corresponds to a number of natural hierarchically organized domains, e.g., organization (“org”) chart  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"
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 50 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 (e.g. DB2, ORACLE, MS SQL Server, SYBASE, INFORMIX).  Several free open source implementations, e.g. MySQL, PostgreSQL  Currently most dominant for developing database applications.  SQL relational standards: SQL-89 (SQL1), SQL-92 (SQL2), SQL-99, SQL3, …  Chapters 5 through 11 describe this model in detail
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 51 History of Data Models  Object-oriented Data Models:  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 Database Standard: ODMG-93, ODMG-version 2.0, ODMG-version 3.0.  Chapters 20 and 21 describe this model.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 52 History of Data Models  Object-Relational Models:  Most Recent Trend. Started with Informix Universal Server.  Relational systems incorporate concepts from object databases leading to object-relational.  Exemplified in the latest versions of Oracle-10i, DB2, and SQL Server and other DBMSs.  Standards included in SQL-99 and expected to be enhanced in future SQL standards.  Chapter 22 describes this model.
Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe Slide 2- 53 Summary  Data Models and Their Categories  History of Data Models  Schemas, Instances, and States  Three-Schema Architecture  Data Independence  DBMS Languages and Interfaces  Database System Utilities and Tools  Centralized and Client-Server Architectures  Classification of DBMSs

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ch02-Database System Concepts and Architecture.ppt

  • 1.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 1
  • 2.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Chapter 2 Database System Concepts and Architecture
  • 3.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 3 Outline  Data Models and Their Categories  History of Data Models  Schemas, Instances, and States  Three-Schema Architecture  Data Independence  DBMS Languages and Interfaces  Database System Utilities and Tools  Centralized and Client-Server Architectures  Classification of DBMSs
  • 4.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 4 Data Models  Data Model:  A set of concepts to describe the structure of a database, the operations for manipulating these structures, and certain constraints that the database should obey.  Data Model Structure and Constraints:  Constructs are used to define the database structure  Constructs typically include elements (and their data types) as well as groups of elements (e.g. entity, record, table), and relationships among such groups  Constraints specify some restrictions on valid data; these constraints must be enforced at all times
  • 5.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 5 Data Models (continued)  Data Model Operations:  These operations are used for specifying database retrievals and updates by referring to the constructs of the data model.  Operations on the data model may include basic model operations (e.g. generic insert, delete, update) and user-defined operations (e.g. compute_student_gpa, update_inventory)
  • 6.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 6 Categories of Data Models  Conceptual (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. These are usually specified in an ad-hoc manner through DBMS design and administration manuals  Implementation (representational) data models:  Provide concepts that fall between the above two, used by many commercial DBMS implementations (e.g. relational data models used in many commercial systems).
  • 7.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 7 Schemas versus Instances  Database Schema:  The description of a database.  Includes descriptions of the database structure, data types, and the constraints on the database.  Schema Diagram:  An illustrative display of (most aspects of) a database schema.  Schema Construct:  A component of the schema or an object within the schema, e.g., STUDENT, COURSE.
  • 8.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 8 Schemas versus Instances  Database State:  The actual data stored in a database at a particular moment in time. This includes the collection of all the data in the database.  Also called database instance (or occurrence or snapshot).  The term instance is also applied to individual database components, e.g. record instance, table instance, entity instance
  • 9.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 9 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 state when it is initially loaded into the system.  Valid State:  A state that satisfies the structure and constraints of the database.
  • 10.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 10 Database Schema vs. Database State (continued)  Distinction  The database schema changes very infrequently.  The database state changes every time the database is updated.  Schema is also called intension.  State is also called extension.
  • 11.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 11 Example of a Database Schema
  • 12.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 12 Example of a database state
  • 13.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 13 Three-Schema Architecture  Proposed to support DBMS characteristics of:  Program-data independence.  Support of multiple views of the data.  Not explicitly used in commercial DBMS products, but has been useful in explaining database system organization
  • 14.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 14 Three-Schema Architecture  Defines DBMS schemas at three levels:  Internal schema at the internal level to describe physical storage structures and access paths (e.g indexes).  Typically uses a physical data model.  Conceptual schema at the conceptual level to describe the structure and constraints for the whole database for a community of users.  Uses a conceptual or an implementation data model.  External schemas at the external level to describe the various user views.  Usually uses the same data model as the conceptual schema.
  • 15.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 15 The three-schema architecture
  • 16.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 16 Three-Schema Architecture  Mappings among schema levels are needed to transform requests and data.  Programs refer to an external schema, and are mapped by the DBMS to the internal schema for execution.  Data extracted from the internal DBMS level is reformatted to match the user’s external view (e.g. formatting the results of an SQL query for display in a Web page)
  • 17.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 17 Data Independence  Logical Data Independence:  The capacity to change the conceptual schema without having to change the external schemas and their associated application programs.  Physical Data Independence:  The capacity to change the internal schema without having to change the conceptual schema.  For example, the internal schema may be changed when certain file structures are reorganized or new indexes are created to improve database performance
  • 18.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 18 Data Independence (continued)  When a schema at a lower level is changed, only the mappings between this schema and higher- level schemas need to be changed in a DBMS that fully supports data independence.  The higher-level schemas themselves are unchanged.  Hence, the application programs need not be changed since they refer to the external schemas.
  • 19.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 19 DBMS Languages  Data Definition Language (DDL)  Data Manipulation Language (DML)  High-Level or Non-procedural Languages: These include the relational language SQL  May be used in a standalone way or may be embedded in a programming language  Low Level or Procedural Languages:  These must be embedded in a programming language
  • 20.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 20 DBMS Languages  Data Definition Language (DDL):  Used by the DBA and database designers to specify the conceptual schema of a database.  In many DBMSs, the DDL is also used to define internal and external schemas (views).  In some DBMSs, separate storage definition language (SDL) and view definition language (VDL) are used to define internal and external schemas.  SDL is typically realized via DBMS commands provided to the DBA and database designers
  • 21.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 21 DBMS Languages  Data Manipulation Language (DML):  Used to specify database retrievals and updates  DML commands (data sublanguage) can be embedded in a general-purpose programming language (host language), such as COBOL, C, C+ +, or Java.  A library of functions can also be provided to access the DBMS from a programming language  Alternatively, stand-alone DML commands can be applied directly (called a query language).
  • 22.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 22 Types of DML  High Level or Non-procedural Language:  For example, the SQL relational language  Are “set”-oriented and specify what data to retrieve rather than how to retrieve it.  Also called declarative languages.  Low Level or Procedural Language:  Retrieve data one record-at-a-time;  Constructs such as looping are needed to retrieve multiple records, along with positioning pointers.
  • 23.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 23 DBMS Interfaces  Stand-alone query language interfaces  Example: Entering SQL queries at the DBMS interactive SQL interface (e.g. SQL*Plus in ORACLE)  Programmer interfaces for embedding DML in programming languages  User-friendly interfaces  Menu-based, forms-based, graphics-based, etc.
  • 24.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 24 DBMS Programming Language Interfaces  Programmer interfaces for embedding DML in a programming languages:  Embedded Approach: e.g embedded SQL (for C, C++, etc.), SQLJ (for Java)  Procedure Call Approach: e.g. JDBC for Java, ODBC for other programming languages  Database Programming Language Approach: e.g. ORACLE has PL/SQL, a programming language based on SQL; language incorporates SQL and its data types as integral components
  • 25.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 25 User-Friendly DBMS Interfaces  Menu-based, popular for browsing on the web  Forms-based, designed for naïve users  Graphics-based  (Point and Click, Drag and Drop, etc.)  Natural language: requests in written English  Combinations of the above:  For example, both menus and forms used extensively in Web database interfaces
  • 26.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 26 Other DBMS Interfaces  Speech as Input and Output  Web Browser as an interface  Parametric interfaces, e.g., bank tellers using function keys.  Interfaces for the DBA:  Creating user accounts, granting authorizations  Setting system parameters  Changing schemas or access paths
  • 27.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 27 Database System Utilities  To perform certain functions such as:  Loading data stored in files into a database. Includes data conversion tools.  Backing up the database periodically on tape.  Reorganizing database file structures.  Report generation utilities.  Performance monitoring utilities.  Other functions, such as sorting, user monitoring, data compression, etc.
  • 28.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 28 Other Tools  Data dictionary / repository:  Used to store schema descriptions and other information such as design decisions, application program descriptions, user information, usage standards, etc.  Active data dictionary is accessed by DBMS software and users/DBA.  Passive data dictionary is accessed by users/DBA only.
  • 29.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 29 Other Tools  Application Development Environments and CASE (computer-aided software engineering) tools:  Examples:  PowerBuilder (Sybase)  JBuilder (Borland)  JDeveloper 10G (Oracle)
  • 30.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 30 Typical DBMS Component Modules
  • 31.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 31 Centralized and Client-Server DBMS Architectures  Centralized DBMS:  Combines everything into single system including- DBMS software, hardware, application programs, and user interface processing software.  User can still connect through a remote terminal – however, all processing is done at centralized site.
  • 32.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 32 A Physical Centralized Architecture
  • 33.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 33 Basic 2-tier Client-Server Architectures  Specialized Servers with Specialized functions  Print server  File server  DBMS server  Web server  Email server  Clients can access the specialized servers as needed
  • 34.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 34 Logical two-tier client server architecture
  • 35.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 35 Clients  Provide appropriate interfaces through a client software module to access and utilize the various server resources.  Clients may be diskless machines or PCs or Workstations with disks with only the client software installed.  Connected to the servers via some form of a network.  (LAN: local area network, wireless network, etc.)
  • 36.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 36 DBMS Server  Provides database query and transaction services to the clients  Relational DBMS servers are often called SQL servers, query servers, or transaction servers  Applications running on clients utilize an Application Program Interface (API) to access server databases via standard interface such as:  ODBC: Open Database Connectivity standard  JDBC: for Java programming access  Client and server must install appropriate client module and server module software for ODBC or JDBC  See Chapter 9
  • 37.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 37 Two Tier Client-Server Architecture  A client program may connect to several DBMSs, sometimes called the data sources.  In general, data sources can be files or other non-DBMS software that manages data.  Other variations of clients are possible: e.g., in some object DBMSs, more functionality is transferred to clients including data dictionary functions, optimization and recovery across multiple servers, etc.
  • 38.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 38 Three Tier Client-Server Architecture  Common for Web applications  Intermediate Layer called Application Server or Web Server:  Stores the web connectivity software and the business logic part of the application used to access the corresponding data from the database server  Acts like a conduit for sending partially processed data between the database server and the client.  Three-tier Architecture Can Enhance Security:  Database server only accessible via middle tier  Clients cannot directly access database server
  • 39.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 39 Three-tier client-server architecture
  • 40.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 40 Classification of DBMSs  Based on the data model used  Traditional: Relational, Network, Hierarchical.  Emerging: Object-oriented, Object-relational.  Other classifications  Single-user (typically used with personal computers) vs. multi-user (most DBMSs).  Centralized (uses a single computer with one database) vs. distributed (uses multiple computers, multiple databases)
  • 41.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 41 Variations of Distributed DBMSs (DDBMSs)  Homogeneous DDBMS  Heterogeneous DDBMS  Federated or Multidatabase Systems  Distributed Database Systems have now come to be known as client-server based database systems because:  They do not support a totally distributed environment, but rather a set of database servers supporting a set of clients.
  • 42.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 42 Cost considerations for DBMSs  Cost Range: from free open-source systems to configurations costing millions of dollars  Examples of free relational DBMSs: MySQL, PostgreSQL, others  Commercial DBMS offer additional specialized modules, e.g. time-series module, spatial data module, document module, XML module  These offer additional specialized functionality when purchased separately  Sometimes called cartridges (e.g., in Oracle) or blades  Different licensing options: site license, maximum number of concurrent users (seat license), single user, etc.
  • 43.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 43 History of Data Models  Network Model  Hierarchical Model  Relational Model  Object-oriented Data Models  Object-Relational Models
  • 44.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 44 History of Data Models  Network Model:  The first network DBMS was implemented by Honeywell in 1964-65 (IDS System).  Adopted heavily due to the support by CODASYL (Conference on Data Systems Languages) (CODASYL - DBTG report of 1971).  Later implemented in a large variety of systems - IDMS (Cullinet - now Computer Associates), DMS 1100 (Unisys), IMAGE (H.P. (Hewlett-Packard)), VAX -DBMS (Digital Equipment Corp., next COMPAQ, now H.P.).
  • 45.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 45 Example of Network Model Schema
  • 46.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 46 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.
  • 47.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 47 Network Model  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”
  • 48.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 48 History of Data Models  Hierarchical Data Model:  Initially implemented in a joint effort by IBM and North American Rockwell around 1965. Resulted in the IMS family of systems.  IBM’s IMS product had (and still has) a very large customer base worldwide  Hierarchical model was formalized based on the IMS system  Other systems based on this model: System 2k (SAS inc.)
  • 49.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 49 Hierarchical Model  Advantages:  Simple to construct and operate  Corresponds to a number of natural hierarchically organized domains, e.g., organization (“org”) chart  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"
  • 50.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 50 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 (e.g. DB2, ORACLE, MS SQL Server, SYBASE, INFORMIX).  Several free open source implementations, e.g. MySQL, PostgreSQL  Currently most dominant for developing database applications.  SQL relational standards: SQL-89 (SQL1), SQL-92 (SQL2), SQL-99, SQL3, …  Chapters 5 through 11 describe this model in detail
  • 51.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 51 History of Data Models  Object-oriented Data Models:  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 Database Standard: ODMG-93, ODMG-version 2.0, ODMG-version 3.0.  Chapters 20 and 21 describe this model.
  • 52.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 52 History of Data Models  Object-Relational Models:  Most Recent Trend. Started with Informix Universal Server.  Relational systems incorporate concepts from object databases leading to object-relational.  Exemplified in the latest versions of Oracle-10i, DB2, and SQL Server and other DBMSs.  Standards included in SQL-99 and expected to be enhanced in future SQL standards.  Chapter 22 describes this model.
  • 53.
    Copyright © 2007Ramez Elmasri and Shamkant B. Navathe Slide 2- 53 Summary  Data Models and Their Categories  History of Data Models  Schemas, Instances, and States  Three-Schema Architecture  Data Independence  DBMS Languages and Interfaces  Database System Utilities and Tools  Centralized and Client-Server Architectures  Classification of DBMSs