databaseim isu1 fundamentals of database systems chapter 2 database system concepts and architecture
TRANSCRIPT
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IM ISU 1Database
Fundamentals of Database Systems
Chapter 2
Database System Concepts andArchitecture
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IM ISU 2Database
Data Models Definition
A set of concepts to describe the structure of a database, and certain constraints that the database should obey
Most data models also include a set of basic operations for specifying retrievals and updates on the database
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IM ISU 3Database
Data Models (cont.)
Categories of data models Conceptual (high-level, semantic) data
models» Provide concepts that are close to the way many
users perceive data» e.g., Entity-relationship model, object data model
Physical (low-level, internal) data models» Provide concepts that describe details of how
data is stored in the computer
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IM ISU 4Database
Data Models (cont.)
Implementation (record-oriented) data models » Provide concepts that fall between the above two,
balancing user views with some computer storage details
» e.g., relational model, hierarchical model, network model
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IM ISU 5Database
Data Models (cont.)
History of data models Relational Model
» Proposed in 1970 by E.F. Codd (IBM) » First commercial system in 1981-82 » e.g., ORACLE, SYBASE, SQL Server
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IM ISU 6Database
Data Models (cont.)
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IM ISU 7Database
Data Models (cont.)
Network Model » The first one to be implemented by Honeywell in
1964-65 (IDS System) » Adopted heavily due to the support by CODASY
L (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)
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IM ISU 8Database
Data Models (cont.)
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IM ISU 9Database
Data Models (cont.)
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
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IM ISU 10Database
Data Models (cont.)
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IM ISU 11Database
Data Models (cont.)
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
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IM ISU 12Database
Data Models (cont.)
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
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IM ISU 13Database
Schemas vs Instances
Database Schema The description of a database Includes descriptions of the database
structure and the constraints that should hold on the database
Can be displayed as a diagram (called schema diagram)
Database schema changes very infrequently
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IM ISU 14Database
Schemas vs Instances (cont.) Example schema diagram
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IM ISU 15Database
Schemas vs Instances (cont.)
Database Instance The actual data stored in a database at a
particular moment in time Also called database state (or occurrence) The database state changes every time the
database is updated» e.g., insert or delete a record
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IM ISU 16Database
Schemas vs Instances (cont.)
Example database state
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IM ISU 17Database
Schema Architecture
Three-Schema Architecture Internal schema
» Describe data storage structures and access paths at the internal level
» Typically uses a physical data model
Conceptual schema » Describe the structure and constraints for the
database at the conceptual level» Uses a conceptual or an implementation data
model
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IM ISU 18Database
Schema Architecture (cont.)
External schemas » Describe the various user views at the external
level to » Usually uses the same data model as the
conceptual level
Purposes » Support program-data independence» Support of multiple views of the data
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IM ISU 19Database
DBMS Architecture (cont.)
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IM ISU 20Database
Data Independence
Logical Data Independence The capacity to change the conceptual
schema without having to change the external schemas and their application programs
Only view definition and the mapping need be change
e.g., Changing the Grade_Report
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IM ISU 21Database
DBMS Architecture (cont.)
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IM ISU 22Database
Data Independence (cont.)
Physical Data Independence The capacity to change the internal schema
without having to change the conceptual schema
e.g., providing an access path by Semester and Year
should not change query “list all sections offered in fall 1998”
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IM ISU 23Database
DBMS Languages
Data Definition Language (DDL) Used by the DBA and database designers to s
pecify the conceptual schema In many DBMSs, DDL is also used to define
conceptual and external schemas (views) In some DBMSs,
» Internal: storage definition language (SDL)» External: view definition language (VDL)
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IM ISU 24Database
DBMS Languages (cont.)
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IM ISU 25Database
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, such as COBOL, PL/1, C/C++
Alternatively, stand-alone DML commands can be applied directly (query language)
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IM ISU 26Database
DBMS Languages (cont.)
Example in SQLSELECT BDATE, ADDRESS
FROM EMPLOYEE
WHERE FNAME='John' AND MINIT='B' AND LNAME='Smith'
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IM ISU 27Database
DBMS Languages (cont.)
Example of embedded SQLEXEC SQL
declare c cursor for select customer-name, customer-cityfrom depositor, customer, accountwhere depositor.customer-name = customer.customer-name and depositor account-number = account.account-number
and account.balance > :amountEND-EXEC
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IM ISU 28Database
Database System Environment
DBMS component modules Database system utilities Tools
CASE tools, data dictionary
Application environment e.g., PowerBuilder
Communication facilities
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IM ISU 29Database
DBMS Component Modules
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IM ISU 30Database
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
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IM ISU 31Database
DBMS Architectures (cont.)
A physical centralized architecture
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IM ISU 32Database
DBMS Architectures (cont.)
Basic 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
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IM ISU 33Database
DBMS Architectures (cont.)
Logical client-server architecture
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IM ISU 34Database
DBMS Architectures (cont.)
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
» in some object DBMSs, more functionality is transferred to clients including data dictionary functions, optimization and recovery across multiple servers, etc.
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IM ISU 35Database
DBMS Architectures (cont.) 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 data from 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
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IM ISU 36Database
DBMS Architectures (cont.)
Logical three tier client-server architecture
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IM ISU 37Database
Classification of DBMSs
Based on the data model used Traditional: Relational, Network, Hierarchica
l Emerging: Object-oriented, Object-relational
Based on the number of users Single-user (typically used with micro- comp
uters) multi-user (most DBMSs)
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IM ISU 38Database
Classification of DBMSs (cont.)
Based on the number of sites Centralized (uses a single computer with one
database) Distributed (uses multiple computers,
multiple databases)» Homogeneous» Heterogeneous (Federated DBMS)