Database Environment - PowerPoint PPT Presentation

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Database Environment

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Transparencies for Chapter 2 of textbook Database Systems: A Practical Approach to Design, Implementation and Management – PowerPoint PPT presentation

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Title: Database Environment


1
Chapter 17
  • Database Environment

1
2
Chapter 17 - Objectives
  • The purpose and origin of the three-level
    database architecture.
  • The contents of the external, conceptual and
    internal levels.
  • The purpose of the external/conceptual and the
    conceptual/internal mappings.

2
3
Chapter 17 - Objectives
  • The meaning of logical and physical data
    independence.
  • The distinction between a Data Definition
    Language (DDL) and a Data Manipulation Language
    (DML).
  • A classification of data models.

3
4
Chapter 17 - Objectives
  • The purpose and importance of conceptual
    modeling.
  • The typical functions and services a DBMS should
    provide.
  • The components of a DBMS.

4
5
Chapter 17 - Objectives
  • The meaning of the clientserver architecture and
    the advantages of this type of architecture for a
    DBMS.
  • The function and importance of the system catalog.

5
6
Objectives of Three-Level Architecture
  • All users should be able to access same data.
  • A user's view is immune to changes made in other
    views.
  • Users should not need to know physical database
    storage details.

6
7
Objectives of Three-Level Architecture
  • DBA should be able to change database storage
    structures without affecting the users' views.
  • Internal structure of database should be
    unaffected by changes to physical aspects of
    storage.
  • DBA should be able to change conceptual structure
    of database without affecting all users.

7
8
ANSI-SPARC Three-level Architecture
8
9
ANSI-SPARC Three-level Architecture
  • External Level
  • Users' view of the database. Describes that part
    of database that is relevant to a particular
    user.
  • Conceptual Level
  • Community view of the database. Describes what
    data is stored in database and relationships
    among the data.

9
10
ANSI-SPARC Three-level Architecture
  • Internal Level
  • Physical representation of the database on the
    computer. Describes how the data is stored in
    the database.

10
11
An example of the three levels
  •  
  • External level
  • 01 employee,
  • 02 employee_city pic
    x(20),
  • 02 employee_state
    pic x(2).

  • conceptual level
  • employee
  • employee_city
    varchar(20)
  • employee_state
    char(2)
  • Internal Level
  • employee
  • employee_city varchar(20) NULl
  • employee_state
    char(2) NOT NULL

12
Differences between Three Levels of ANSI-SPARC
Architecture
11
13
Data Independence
  • Logical Data Independence
  • Refers to immunity of external schemas to changes
    in conceptual schema.
  • Conceptual schema changes e.g. addition/removal
    of entities.
  • Should not require changes to external schema or
    rewrites of application programs.

12
14
Data Independence
  • Physical Data Independence
  • Refers to immunity of conceptual schema to
    changes in the internal schema.
  • Internal schema changes e.g. using different file
    organizations, storage structures/devices.
  • Should not require change to conceptual or
    external schemas.

13
15
Data Independence and the ANSI-SPARC Three-level
Architecture
14
16
Data Model
  • Collection of concepts for describing data,
    relationships between data and constraints on the
    data in an organization.
  • Data Model comprises
  • A structural part (a set of rules according to
  • Which databases can be constructed)
  • A manipulative part (defining the types of
    operations that are allowed on the data)
  • Possibly a set of integrity rules

18
17
Data Model
  • Purpose
  • To represent the data in an understandable way.
  • Categories of data models include
  • Conceptual
  • Logical (Functional)
  • Physical

19
18
Conceptual modeling
  • The process of developing a conceptual data model
    that is
  • a complete and accurate representation of an
    organization's data requirements.
  • independent of implementation details.

22
19
Functions of a DBMS
  • Data Storage, Retrieval and Update.
  • Must furnish users with the ability to store,
    retrieve, and update data in the database.
  • A User-Accessible Catalog.
  • Must furnish a catalog in which descriptions of
    data items are stored and which is accessible to
    users.

23
20
Functions of a DBMS
  • Transaction Support
  • Must furnish a mechanism to ensure that either
    all the updates corresponding to a given
    transaction are made or that none of them are
    made.
  • Concurrency Control Services
  • Must furnish a mechanism to ensure that database
    is updated correctly when multiple users are
    updating the database concurrently.

24
21
Functions of a DBMS
  • Recovery Services
  • Must furnish a mechanism for recovering the
    database in the event that the database is
    damaged in any way.
  • Authorization Services
  • Must furnish a mechanism to ensure that only
    authorized users can access the database.

25
22
Functions of a DBMS
  • Support for Data Communication
  • Must be capable of integrating with communication
    software.
  • Integrity Services
  • Must furnish a means to ensure that both the data
    in the database and changes to the data follow
    certain rules.

26
23
Functions of a DBMS
  • Services to Promote Data Independence
  • Must include facilities to support the
    independence of programs from the actual
    structure of the database.
  • Utility Services
  • Should provide a set of utility services.

27
24
Components of a DBMS
28
25
Components of a DBMS
  • Query processor
  • Database manager (DM)
  • File manager
  • DML preprocessor
  • DDL compiler
  • Catalog manager

29
26
Components of Database Manager (DM)
30
27
Components of Database Manager (DM)
  • Authorization control
  • Command processor
  • Integrity checker
  • Query optimizer
  • Transaction manager
  • Scheduler
  • Recovery manager
  • Buffer manager

31
28
Multi-user DBMS Architectures
  • Teleprocessing
  • File-server
  • Client-server

32
29
Teleprocessing
  • Traditional architecture.
  • Single mainframe with a number of terminals
    attached.
  • Trend is now towards downsizing.

33
30
Teleprocessing Topology
34
31
File-server
  • File-server is connected to several workstations
    across a network.
  • Database resides on file-server.
  • DBMS and applications run on each workstation.

35
32
File-server
  • Disadvantages include
  • Significant network traffic.
  • Copy of DBMS on each workstation.
  • Concurrency, recovery and integrity control more
    complex.

36
33
File-server Architecture
37
34
Client-server
  • Server holds the database and the DBMS.
  • Client manages the user interface and runs
    applications.

38
35
Client-server
  • Advantages include
  • Wider access to existing databases.
  • Increased performance.
  • Possible reduction in hardware costs.
  • Reduction in communication costs.
  • Increased consistency.

39
36
Client-server Architecture
40
37
System Catalog
  • A repository of information (metadata) describing
    the data in the database.
  • Typically stores
  • Names of authorized users.
  • Names of data items in the database.
  • Constraints on each data item.
  • Data items accessible by a user and the type of
    access.

43
38
System Catalog
  • It is used by modules such as
  • Authorization Control.
  • Integrity Checker.

44
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