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cse3330-spring12-Ch2 (2).ppt
1.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 2 Database System Concepts and Architecture
2.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 2 Outline • Data Models and Their Categories • Schemas, Instances, and States • Three-Schema Architecture and Data Independence • DBMS Languages and Interfaces • Database System Architectures • Classification of DBMSs • History of Data Models
3.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Data Models • Data Model: – A set of concepts to describe the structure of a database, the operations for manipulating the data, and the constraints that the data should follow. • Data Model Structure and Constraints: – Data Model constructs define the database structure – Data model constructs often include: data elements and their data types (often called attributes); grouping of related elements into entities (also called objects or records or tuples); and relationships among entities – Constraints specify restrictions on the stored data; the data that satisfies the constraints is called valid data
4.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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)
5.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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).
6.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Database Schema versus Database State • Database Schema: – The description of a database. – Includes descriptions of the database structure, relationships, data types, and constraints • Schema Diagram: – An illustrative 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, Name
7.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Database Schema vs. Database State (cont.) • 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 a database instance (or occurrence or snapshot). • NOTE: The term instance is also used to refer to individual database components, e.g. a record instance, table instance, or entity instance
8.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Database Schema vs. Database State • Database State: – Refers to the content of a database at a particular 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.
9.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Database Schema vs. Database State (cont.) • 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.
10.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Example of a Database Schema
11.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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
12.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Three-Schema Architecture (cont.) • 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 an implementation (or a conceptual) data model. – External schemas at the external level to describe the various user views. • Usually uses the same data model as the conceptual schema.
13.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley The three-schema architecture (cont.) transcript tables
14.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Three-Schema Architecture (cont.) • Mappings among schema levels are needed to transform requests and data. – Users and 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 as a Web page)
15.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Data Independence • Logical Data Independence: – The capacity to change the conceptual schema without having to change the external schemas and their associated application programs. – re-organize tables • 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
16.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Data Independence (cont.) • 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.
17.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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). – Theoretically, separate storage definition language (SDL) and view definition language (VDL) can used to define internal and external schemas. In practice: • SDL is typically realized via DBMS commands provided to the DBA and database designers • VDL is typically part of the same language as DDL
18.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley DBMS Languages (cont.) • 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 (see Chapter 13) • 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).
19.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley DBMS Languages (cont.) • Types of DML: – High-Level Declarative (Set-oriented, Non- procedural) Languages, such as the relational language SQL • Specify “what” data to retrieve rather then “how” to retrieve it • May be used in a standalone way or may be embedded in a programming language – Low Level or Procedural (Record-at-a-time) Languages: • Must be embedded in a programming language • Need programming language constructs such as looping
20.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley DBMS Interfaces • Stand-alone query language interfaces – Example: Typing SQL queries directly through the DBMS interactive SQL interface (e.g. SQL*Plus in ORACLE) • Programmer interfaces for embedding DML in programming languages • User-friendly interfaces (often Web-based) – Menu-based, forms-based, graphics-based, etc.
21.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley DBMS Programming Language Interfaces • Programmer interfaces for embedding DML in a programming language (see Chapter 13): – 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
22.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley User-Friendly and Web-based 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
23.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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 storage structures/access paths (physical database)
24.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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.
25.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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.
26.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Other Tools (cont.) • Application Development Environments and CASE (computer-aided software engineering) tools often have a database design component • Examples: – PowerBuilder (Sybase) – JBuilder (Borland) – JDeveloper 10G (Oracle)
27.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Typical DBMS Component Modules naive user
28.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley DBMS Architectures • Centralized DBMS Architecture: – Combines everything into single computer 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 (computer).
29.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley A Physical Centralized Architecture
30.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley DBMS Architectures (cont.) • Basic 2-tier Client-Server Architecture: Specialized Server nodes with Specialized functions – Print server – File server – DBMS server – Web server – Email server • Client nodes can access the specialized servers as needed
31.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Logical two-tier client server architecture
32.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Client nodes • Provide appropriate interfaces through a client software module to access and utilize the various server resources. • Clients may be PCs or Workstations (or even diskless machines) with the client software installed. • Connected to the servers via a network. – LAN: local area network – wireless network – etc.
33.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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 13
34.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Two Tier Client-Server DBMS Architecture • A program running at a client may connect to several DBMSs (also called data sources). • In general, data sources can be files or other non- DBMS software that manages data. • Client focuses on user interface interactions and only accesses database when needed. • In some cases (e.g. some object DBMSs), more functionality is transferred to clients (e.g. data dictionary functions, optimization and recovery across multiple servers, etc.)
35.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Three Tier Client-Server DBMS Architecture • Common for Web applications • Third intermediate layer (middle tier) called Application Server or Web Server: – Stores the web connectivity software and the business logic part of the application – Accesses and updates data on 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
36.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Three-tier client-server architecture
37.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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, see Chapter 25)
38.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley 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 DBMSs 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.
39.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley History of Data Models • Network Model • Hierarchical Model • Relational Model • Object-oriented Data Models • Object-Relational Models
40.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley History of Data Models (cont.) • Network Model: – The first network DBMS was implemented by Honeywell in 1964-65 (IDS System). – Adopted heavily due to the standard 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.).
41.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Example of Network Model Schema
42.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Network Model • Advantages: – Can model complex relationships among records 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.
43.
Copyright © 2011
Pearson Education, Inc. Publishing as Pearson Addison-Wesley Network Model • Disadvantages: – Navigational and procedural nature of processing requires programming access – Intermixes storage structures with conceptual modeling relationships – Database contains a complex array of pointers that thread through a set of records. • Little scope for automated “query optimization”
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Pearson Education, Inc. Publishing as Pearson Addison-Wesley History of Data Models (cont.) • 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 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.)
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Pearson Education, Inc. Publishing as Pearson Addison-Wesley Hierarchical Model • Advantages: – Can implement certain tasks very efficiently – Easy to store hierarchically organized data, e.g., organization (“org”) charts • Disadvantages: – Navigational and procedural nature of processing – Difficult to store databases where multiple relationships exist among the data records – Little scope for “query optimization” by system (programmer must optimize the programs) – Language is procedural: Uses constructs like GET, GET UNIQUE, GET NEXT, GET NEXT WITHIN PARENT, etc.
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Pearson Education, Inc. Publishing as Pearson Addison-Wesley History of Data Models (cont.) • Relational Model: – Proposed in 1970 by E.F. Codd (IBM), first commercial systems in early 1980s. – Now in many 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, SQL-2008 – Chapters 3 through 6 describe this model in detail
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Pearson Education, Inc. Publishing as Pearson Addison-Wesley History of Data Models (cont.) • Object-oriented Data Models: – Allow databases to be used seamlessly with object-oriented programming languages. – Can store persistent objects created in O-O Programming Languages such as C++ (e.g., in OBJECTSTORE or VERSANT), and Smalltalk (e.g., in GEMSTONE). – Other experimental systems include 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. – Chapter 11 describes this model.
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Pearson Education, Inc. Publishing as Pearson Addison-Wesley History of Data Models (cont.) • Object-Relational Models: – Relational systems incorporated concepts from object databases leading to object-relational. – Exemplified in the latest versions of Oracle-10i, DB2, and SQL Server and other DBMSs. – Standards started in SQL-99 and enhanced in SQL-2008. – Chapter 11 also describes this model.
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Pearson Education, Inc. Publishing as Pearson Addison-Wesley Summary • Data Models and Their Categories • Schemas, Instances, and States • Three-Schema Architecture • Data Independence • DBMS Languages and Interfaces • Centralized and Client-Server Architectures • Classification of DBMSs • History of Data Models
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