Database Management System

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Database Management System

• Chapter 1 An Overview

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• Bit 0 or 1
• Byte 1 Byte consists of 8 Bits ( 1 Byte is
  one character)
• Ex. 01000001 represents a character
  A
• Word A word consists of several bytes.
• Field A field or an attribute is a boundary
  of data.
• Record A record consists of a group of field
  values that represent
• one person or one thing.
• File A file consists of several records
  that share the same
• structure.
• Data Base A Database consists of several
  related files.

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THE TRADITIONAL FILE ENVIRONMENT
A data file is a collection of logically related
records. In a file management environment,
each application has a specific data file related
to it, containing all the data records needed by
the application.
Registrars office
Class programs
Class file
Employee data
Student data

• Employee data contains information of the
  instructor
• who is an employee.
• Student data is repeated.

Course data
Registration data
Accounting dept.
Accounts file
Accounts programs
Employee data
Student data
Tuition data
Financial aid
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Problems with the File processing
Program Data Dependence
Program Data Dependence is the tight
relationship between data stored in various files
and the specific programming language used to
access or execute them. Every traditional
computer program has to describe the input file
format with which it works. Program Data
Dependence leads to the potential for Data
redundancy.
Data Redundancy is the presence of duplicate data
in multiple data files. Data redundancy occurs
when different divisions, functional areas, and
groups in an organization independently collect
the same piece of data and build separately their
own systems with different languages, platforms,
and data file format . Data Redundancy leads to
the potential for data inconsistency.
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Data Isolation File processing can leads to
difficulty in accessing data from different
applications. (Data can not be shared). With
applications uniquely designed and implemented,
data are scattered in various files, and files
may be in different formats.
Integrity problems The data values stored in
the database must satisfy certain types of
consistency constraints. Developers enforce these
constraints in the system by adding appropriate
code in the various application programs.
However, when new constraints are added, it is
difficult to change the programs to enforce them.
Security problems Enforcing security
constraints in the application is much more
difficult than that of in the database
environment. Not every user of the database
system should be able to access all the data.
Applications should not have to be developed with
regard to how the data are stored. That is, the
applications and data in computer systems should
be independent - a characteristic called
application/data independence.
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Databases The modern approach
Registrars office
Class programs
Academic info
Student data
Database management system
Course data
Accounting dept.
Accounts programs
Registration data
Employee data
Team data
Athletics dept.
Sports programs
Tuition data
Financial aid
A database, which is a logical group of related
files, can eliminate many of the problems
associated with a traditional file environment.
With the database approach, all the data
are typically contained in the same storage
location, rather than residing in many different
files across the organization. Unlike the
traditional approach, in which different programs
access the different data files, the database is
arranged so that one set of software programs
(DBMS) provides access to all the data.
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DBMS Database Management System

• DBMS consists of a collection of interrelated
  data and a set of programs
• to access those data. The primary goal of DBMS
  is to provide an
• environment that is both convenient and efficient
  to use in retrieving
• and storing database information. DBMS acts as
  the interface software
• between users and data stored in the database by
  hiding the detail of
• internal

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The enterprise system collects data from various
key business processes and stores the data in a
single comprehensive data repository where they
can be used by other parts of the business
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Locating Data in Databases
A centralized database has all the related files
in one physical location.
Central Location
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Locating Data in Databases
A distributed database has complete copies of a
database, or portions of a database, in more
than one location.
Location B
Location A
Central Location
Location C
Location D
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• There are two types of distributed databases
• replicated
• partitioned

A replicated database has complete copies of the
entire database in many locations, primarily to
alleviate the single-point-of-failure problems of
a centralized database as well as to increase
user access responsiveness.
A partitioned database is subdivided, so that
each location has a portion of the entire
database (usually the portion that meets users
local needs). This type of database provides the
response speed of localized files without the
need to replicate all changes in multiple
locations.
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Databases The modern approach
Registrars office
Class programs
Academic info
Student data
Database management system
Course data
Accounting dept.
Accounts programs
Registration data
Employee data
Team data
Athletics dept.
Sports programs
Tuition data
Financial aid
A database, which is a logical group of related
files, can eliminate many of the problems
associated with a traditional file environment.
With the database approach, all the data
are typically contained in the same storage
location, rather than residing in many different
files across the organization. Unlike the
traditional approach, in which different programs
access the different data files, the database is
arranged so that one set of software programs
(DBMS) provides access to all the data.
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Abstract View of Data
DBMS provides the ability for many
different users to share data and process
resources. How can a single, unified database
meet the differing requirements of so many
users? That is, the system hides certain details
of how the data are stored and maintained.
A DBMS minimizes these problems by providing
3 views of the database data (Since many
database-systems users are not computer trained,
developers hide the complexity from users through
several levels of abstraction A physical
view The lowest level of abstraction describes
how the data are actually stored. It deals with
the actual, physical arrangement and location of
data in the direct access storage devices
(DASDs). A logical view The next
higher level of abstraction describes what data
are stored in the database, and what
relationships exist among those data. The
logical describes the entire database in terms of
a small number of relatively simple
structures.(Users may not want to know all the
technical details of physical storage.
An external view The higher level of
abstraction describes only part of the entire
database. Many users of the database do not need
all this information instead, they need to
access only a part of the database.
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Data Abstraction
External View 1
External View 2
External View 3
Conceptual (Logical) Level
Physical Level
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Logical User Views Data elements and
relationships needed for Billing, Load Research,
or Maintenance processing
Billing Application
Load Research Application
Maintenance Application
Maintenance Data Model
Billing Research Data Model
Data elements and relationships (the schema)
needed for the support of all information
services.
Information Services Data Model
Database Management System
Software Interface The DBMS provides access to
the information services databases
Service Databases
Physical Data Views Organization and location of
data on the storage media.
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One strength of a DBMS is that while
there is only one physical view of the data,
there can be an endless number of different
external views - one specifically tailored to
each individual user, if necessary.
Data Model Data Model defines how data are
conceptually structured. A collection of
conceptual tools for describing data, data
relationships, data semantics, and consistency
constraints. Examples of data model
hierarchical, network, relational,
object-oriented, entity-relation model,
object-relational, hypermedia, and
multidimensional models.
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Instance ??? Schema

• Instance ???????????? ??????????????????????????
  ???????????????????????? ??????? Instance
  ???????????????????????????????????????????????
  Programming Language ??????????????????????
  ????????????? ??????????????????????????????
  Insert, Delete ???? Update ????????????????
• Schema ???????? (?????????) ????????????????????
  ????????????? ??????????????? ????????????????????
  ?????????????????? ???????????????????????????????
  ????????? ??????????????????????????? (fields)
  ????????

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Instance and Schema

• Instance of Database The collection of
  information stored in the database at a
  particular moment. Instance of Database change
  over time as information is inserted and deleted.
• The concept of instances can be understood by
  analogy to a program written in a programming
  language. Each variable has a particular value at
  any given instant of time.
• Schema The overall design of the database which
  must be specified as following
• What files are included in a database?
• What fields are included in each file?
• How those files are related?
• A database schema corresponds to the variable
  declarations in a program.

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Database Language
A database system provides a Data Definition
Language (DDL) to specify the database schema and
a Data Manipulation Language (DML) to express
database queries and updates.
Data Definition Language (DDL) A database
schema can be specified by a set of definitions
expressed by a special language called a
Data-Definition Language. DDL defines what types
of information are in the database and how they
will be structured. The DDL defines each data
element as it appears in the database before that
data element is translated into the forms
required by the applications.
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Database Languages
Examples of Data Definition Language (DDL)
CREATE TABLE CREATE VIEW CREATE
INDEX ALTER TABLE DROP VIEW DROP
INDEX DROP TABLE CREATE TABLE S ( S
Char(5) Not Null, Sname Char(20) Not
Null, Status SmallInt Not Null, City
Char(15) Not Null, PRIMARY KEY (S) )
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After DDL statement has been interpreted, DBMS
generates a special set of tables called the data
dictionary or data directory. A data dictionary
contains metadata that is, data about data. The
schema of a table is an example of metadata. A
database system consults the data dictionary
before reading or modifying actual data.
????????????????????????????????? DDL (DDL
Interpreter) ?????????????????????????????????????
????????????????? ??????????????? (Data
Dictionary) ??????????????????????????
???????????????????????????????????????? ?
??????????????????????????? ???? ??????????????
DBMS ?????????????????????????????????????????
The data values stored in the database must
satisfy certain consistency constraints. The
database systems check these constraints every
time the database is updated.
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Data Manipulation Language (DML)
??????????????????????????? ??????????????? -
???????????????? (RetrieveData) -
?????????????????? (Insert Records) -
??????????????? (Delete Records) -
????????????????????????????? (Update
Fields) ????????????????????????????????
???????????????????????? DBMS ????????????????????
??????????????? (DML is a language that
enables users to access or manipulate data as
ornagized by the appropriate data model.)
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Database Access from Application Programs

• Application Program are written in a Host
  Language. To access the database, DML statements
  need to be executed from the hose language by
• Providing an application program interface (API)
  that can be
• used to send DML and DDL statements to the
  database, and
• retrieve the result. Ex. ODBC, JDBC.
• Extending the host language syntax to embed DML
  calls within
• Host Language program.. However, DML syntax is
  different
• from syntax of Host Language, Query Processor
  of DBMS
• consists of

DDL Interpreter DML Compiler Query Evaluation
Engine
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DDL Interpreter ??? (interpret)
???????????????????????? DDL ?????????????????????
?????? data dictionary DML Compiler ???
(translate) ???????????? DML ?????????????????????
???????? (structure query language) ??????
low-level instructions ??? Query Evaluation
Engine ??????????????? (?????? query 1 ??????
???????????????????????? 1 query evaluation plans
????????????????????????? ??????? ??????????????
DML compiler ??????????? query optimization
?????????? query evaluation plans
???????????????????????? (The DML compler also
performs query optimization that is, it picks
the lowest cost evaluation plan from among the
alternatives.) Query Evaluation Engine ?????
DML Compiler ????? Object Code ??????? Low-level
Instructions ?????????? ???????????????? Query
Evaluation Engine ??????????????????
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Data Consumers
Visual Basic Application
Visual C Application
Other Applications
ASP page
ADO Connection
Service Components
DML Compiler DDL Interpreter Query Evaluation
Engine
Cursor Engine
Query Processor
Data Providers
Simple Data Provider
ODBC Provider
Mainframe Data
Non Relation Data
ODBC
Database Server
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How Database Represent Information

• A database management system (DBMS) is a
  combination of software
• and data
• The physical database
• a collection of files that contain the data
  content.

• The schema
• a specification of the information content of
  the physical database

• The database engine
• software that supports access to and
  modification of the contents of the database

• The data definition and manipulation language
• programming languages that support
  schema definition and database access.

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Overall System Structure

• Query processor components
• DML compiler
• DDL interpreter
• Query evaluation engine

• Storage manager components provides the
  interface between the low level data stored
• in the database and the application programs and
  queries submitted to the system
• Authorization and integrity manager tests
  for the satisfaction of integrity constraints
• and checks the authority of users to access
  data.
• Transaction manager ensures that the
  database remains in a consistent state
• despite system failures and that concurrent
  transaction executions proceed without
• conflicting.
• File manager manages the allocation of
  space on disk storage and the data
• structures used to represent information stored
  on disk.
• Buffer manager responsible for fetching
  data from disk storage into main memory.

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• Data files store the database itself.
• Data dictionary stores metadata about the
  structure of the database.
• The data dictionary is used heavily.
  Therefore, great emphasis
• should be placed on developing a good design
  and efficient
• implementation of the dictionary.
• Indices provide fast access to data items that
  hold particular values.

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Sophisticated users
Application programmers
Database administrator
Naïve users
users
use
use
write
use
Application interfaces
Application programs
Query tools
Administration tools
Compiler and linker
DML compiler
DDL interpreter
query procesor
Application programs object code
DML compiler and organizer
Query evalution engine
Authorization and integrity manager
Storage manager
Transaction manager
Buffer manager
File manager
Disk storage
Data dictionary
Indices
Data files
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Database Processing Advantages

• Data redundancy (Repetition of data) can be
  reduced.
• Data inconsistency can be avoided.
• Data can be shared.
• Standard of data can be controlled.
• Concurrent-access to database can be provided.
• Data Integrity and data security can be
  maintained.

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Business Functions
Marketing and Sales
Human Resources
Accounting
Finance
Manufacturing
Vendors Vendors Vendors
Customer Customer Customer
Business processes
Business processes
Business processes
Business processes
Business processes
Organizational Boundaries
Organizational Boundaries
Human Resources Systems
Marketing and Sales Systems
Manufacturing Systems
Accounting Systems
Finance Systems
Information Systems
Traditional view of systems. In most
organizations, separate systems built over a long
period of time support discrete business
processes and discrete business functions. The
organizations system rarely included vendors
and customers.
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How to integrate functions and business processes
1. Implement a separate middleware bridge to
each of these specialized systems to link
them all together
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How to integrate functions and business processes
1. Implement a separate middleware bridge to
each of these specialized systems to link
them all together
2. Implement or buy entirely new enterprise
applications that can coordinate
activities, decision, and knowledge across many
different functions, levels, and business
units in a firm.

• Enterprise systems
• Supply chain management systems SCM)
• Customer relationship management systems (CRM)

Each of these enterprise applications integrates
a related set of functions and business process
to enhance the performance of the organization as
a whole.
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Enterprise systems also known as enterprise
resource planning (ERP)
The enterprise systems, designed to support
organization- wide, coordinates and integrates
a related set of major internal functions and
business processes to enhance the performance of
the organization as a whole. They solve the
problem of organizational inefficiencies created
by isolated islands of information, business
processes, and technology.
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Manufacturing
Accounting
Business process Business process Business
process Enterprise-wide business Process
Organizational Boundaries
Customers
Vendors
Organizational Boundaries
Marketing and Sales
Human Resources
Finance
Enterprise systems. Enterprise systems can
integrate the key business processes of an entire
firm into a single software system that allows
information to flow seamlessly throughout the
organization. These systems focus primarily on
internal processes but may include transactions
with customers and vendors.