dr. amr mahmoud tolba
TRANSCRIPT
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Copyright 2004 Pearson Education, Inc.
Instructor
Dr. Amr Mahmoud TolbaOffice No : 106 Floor 7Website: http://faculty.ksu.edu.sa/atolba
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Copyright 2004 Pearson Education, Inc.
Chapter 2
Database SystemConcepts andArchitecture
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Slide 2-3Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Data Models
Data Model : A set of concepts to describe thestructure of a database ( the data types, relationships and constraintsthe data types, relationships and constraintsthat should hold for the datathat should hold for the data ), and certain constraints that thedatabase should obey.Data Model Operations : Operations forspecifying database retrievals and updates byreferring to the concepts of the data model.Operations on the data model may include basicoperations and user-defined operations . (An example of An example of useruser --define operation isdefine operation is COMPUTECOMPUTE --GPAGPA which can be applied to thewhich can be applied to the StudentStudent objectobject )
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Slide 2-4Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Categories of Data Models
Conceptual (high-level , semantic ) data models:Provide concepts that are close to the way manyusers perceive data. (Also called entity-based orobject-based data models.)Physical (low-level , internal ) data models:Provide concepts that describe details of how datais stored in the computer.Implementation (representational ) data models:Provide concepts that fall between the above two,balancing user views with some computer storage
details.
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Slide 2-5Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Data Models
Physicalmodel
Logicalmodel
Conceptual
model
Hardware dependentSoftware dependent
Hardware independentSoftware dependent
Hardware independent
Software independent
(low-level , internal )data models
(Representational )data models
(high-level , semantic )
data models
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Slide 2-6Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Data ModelsObject-based conceptual model
Entity-Relationship
Object-Oriented Semantic Functional
- Binary
Record-based logical models
Relational model Network model Hierarchical model
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Slide 2-7Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Data Models
Staff_No LName Salary Brn_No Brn_No Street Tel_No
St1 Name1 7000 1St2 Name2 4000 1St3 Name3 6500 2St4 Name4 3000 3
1 Olayaa 46300002 Malaz 47800003 Rawda 2310000
St1 Name1 7000 Olayaa 4630000
St2 Name2 4000
St3 Name3 6500
St4 Name4 3000
Malaz 4780000
Rawda 2310000
RelationalModel
Network
Model
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Slide 2-8Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Data Models
St3 Name3 6500
HierarchicalModel
St1 Name1 7000 St2 Name2 4000
St4 Name4 3000
Olayaa 4630000Malaz 4780000 Rawda 2310000
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Slide 2-9Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Schemas versus Instances Database Schema : The description of a database.
Includes descriptions of the database structure andthe 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 . Alsocalled database state (or occurrence ).
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Slide 2-10Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Database Schema Vs.Database State Database State: Refers to the content of a databaseat 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 . Thedatabase state changes every time the database is updated.
Schema is also called intension , whereas state is called
extension .
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Slide 2-11Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Three-Schema Architecture
Proposed to support DBMS characteristicsof: Program-data independence . Support of multiple views of the data.
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Slide 2-12Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Three-Schema Architecture
Database
ExternalLevel
InternalLevel InternalDescription
ConceptualDescription
View 2 View nView 1
User 1 User 2 User n
Conceptual
Level
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Slide 2-13Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Three-Schema Architecture
Emp_No FName LName Dept_No Staff_No LName Salary
View 1 View 2
InternalLevel
ConceptualLevel
EMPLOYEEEmp_No CHAR(6)FName CHAR(15)LName CHAR(15)
Dept_No CHAR(3)Salary NUMBER(5)
PREFIX TYPE=BYTE(6),OFFSET=0
EMP# TYPE=BYTE(6),OFFSET=6, INDEX=EMPXLNM TYPE=BYTE(15),OFFSET=12FNM TYPE=BYTE(15),OFFSET=27DPT# TYPE=BYTE(4),OFFSET=42PAY TYPE=FULLWORD,OFFSET=46
ExternalLevel
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Slide 2-15Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Three-Schema Architecture
Mappings among schema levels are neededto transform requests and data. Programsrefer to an external schema, and are mappedby the DBMS to the internal schema forexecution.
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Slide 2-16Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Data Independence
Logical Data Independence : The capacityto change the conceptual schema withouthaving to change the external schemas andtheir application programs.
Physical Data Independence : The capacity
to change the internal schema withouthaving to change the conceptual schema.
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Slide 2-17Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Data Independence
When a schema at a lower level is changed,only the mappings between this schemaand higher-level schemas need to bechanged in a DBMS that fully supports dataindependence. The higher-level schemasthemselves are unchanged . Hence, theapplication programs need not be changedsince they refer to the external schemas.
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Slide 2-18Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Data Independence
InternalSchema
ConceptualSchema
ExternalSchema ExternalSchemaExternalSchema
External/ConceptualMapping
Conceptual/InternalMapping
Logical data Independence
Physical data Independence
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Slide 2-19Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
DBMS Languages
Data Definition Language (DDL ): Used by theDBA and database designers to specify theconceptual schema of a database. In many
DBMSs, the DDL is also used to define internaland external schemas (views). In some DBMSs,separate Storage Definition Language (SDL ) andView Definition Language (VDL ) are used todefine internal and external schemas.
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Slide 2-20Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
DBMS Languages
Data Manipulation Language (DML ):Used to specify database retrievals andupdates.
DML commands ( data sublanguage ) can beembedded in a general-purpose programminglanguage ( host language ), such as COBOL, Cor an Assembly Language.
Alternatively, stand-alone DML commands canbe applied directly ( query language ).
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Slide 2-21Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
DBMS Languages
High Level or Non-proceduralLanguages: e.g., SQL, are set-oriented andspecify what data to retrieve than how toretrieve. Also called declarative languages.
Low Level or Procedural Languages:
record-at-a-time; they specify how toretrieve data and include constructs such aslooping.
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Slide 2-22Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
DBMS Interfaces Stand-alone query language interfaces. Programmer interfaces for embedding DML in
programming languages: Pre-compiler Approach
Procedure (Subroutine) Call Approach User-friendly interfaces:
Menu-based, popular for browsing on the web
Forms-based, designed for nave users Graphics-based (Point and Click, Drag and Drop etc.) Natural language: requests in written English Combinations of the above
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Slide 2-23Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
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 accounts, granting authorizations
Setting system parameters Changing schemas or access path
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Slide 2-25Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Other Tools
Data dictionary / repository : Used to store schema descriptions and other information suchas design decisions, application program descriptions, userinformation, usage standards, etc.
Active data dictionary is accessed by DBMS software andusers/DBA.
Passive data dictionary is accessed by users/DBA only.
Application Development Environments and CASE(computer-aided software engineering) tools:
Examples Power builder (Sybase), Builder (Borland)
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Slide 2-26Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Centralized and Client-ServerArchitectures
Centralized DBMS: combines everythinginto single system including- DBMSsoftware, hardware, application programs
and user interface processing software.
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Slide 2-27Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Basic Client-ServerArchitectures
Specialized Servers with Specializedfunctions Clients DBMS Server
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Slide 2-28Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Specialized Servers withSpecialized functions:
File Servers Printer Servers Web Servers E-mail Servers
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Slide 2-29Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Clients:
Provide appropriate interfaces and a client-versionof the system to access and utilize the serverresources.
Clients maybe diskless machines or PCs orWorkstations with disks with only the clientsoftware installed.
Connected to the servers via some form of anetwork.
(LAN: local area network, wireless network,etc.)
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Slide 2-30Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
DBMS Server
Provides database query and transactionservices to the clients Sometimes called query and transaction
servers
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Slide 2-31Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Two Tier Client-ServerArchitecture
User Interface Programs and ApplicationPrograms run on the client side Interface called ODBC (Open Database
Connectivity see Ch 9 ) provides anApplication program interface (API) allowclient side programs to call the DBMS.Most DBMS vendors provide ODBCdrivers.
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Slide 2-32Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Two Tier Client-ServerArchitecture
A client program may connect to several DBMSs. Other variations of clients are possible: e.g., in
some DBMSs, more functionality is transferred to
clients including data dictionary functions,optimization and recovery across multiple servers,etc. In such situations the server may be called the
Data Server .
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Slide 2-33Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Three Tier Client-ServerArchitecture
Common forWeb applications
Intermediate Layer called Application Server orWeb Server: stores the web connectivity software and the rules and
business logic (constraints) part of the application used toaccess the right amount of data from the database server
acts like a conduit for sending partially processed databetween the database server and the client.
Additional Features- Security: encrypt the data at the server before transmission decrypt data at the client
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Slide 2-34Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
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 micro-
computers) vs. multi-user (most DBMSs).
Centralized (uses a single computer with onedatabase) vs. distributed (uses multiplecomputers, multiple databases)
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Slide 2-35Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Classification of DBMSs
Distributed Database Systems (DDS) havenow 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 serverssupporting a set of clients.
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Slide 2-36Elmasri and Navathe, Fundamentals of Database Systems, Fourth Edition
Copyright 2004 Pearson Education, Inc.
Variations of DistributedEnvironments:
Homogeneous DDBMS Heterogeneous DDBMS Federated or Multidatabase Systems