Data dictionary

Data dictionary is used in database management system

1. WHAT IS A DATA DICTIONARY?WHAT IS A DATA DICTIONARY?
A DATA DICTIONARY IS AN INTEGRAL A DATA DICTIONARY IS AN INTEGRAL
PART OF DATABASE.PART OF DATABASE.
IT HOLDS INFORMATION ABOUT THE IT HOLDS INFORMATION ABOUT THE
DATABASE AND THE DATA THAT IT DATABASE AND THE DATA THAT IT
STORES, i.e. the META-DATA.STORES, i.e. the META-DATA.

2. IntroductIon :IntroductIon :
The data dictionary (or data repository) or The data dictionary (or data repository) or
system catalog is an important part of the system catalog is an important part of the
DBMS. It contains data about data (or DBMS. It contains data about data (or
metadata). It means that it contains the metadata). It means that it contains the
actual database descriptions used by the actual database descriptions used by the
DBMS. In most DBMSs, the data DBMS. In most DBMSs, the data
dictionary is active and integrated. It dictionary is active and integrated. It
means that the DBMS checks the data means that the DBMS checks the data
dictionary every time the database is dictionary every time the database is
accessed.accessed.

3. SOME TYPICAL COMPONENTS SOME TYPICAL COMPONENTS
OF DATA DICTIONARY ENTRY OF DATA DICTIONARY ENTRY
ARE:ARE:

4. ALL WELL DESIGNED DATABASE WILL ALL WELL DESIGNED DATABASE WILL
SURELY INCLUDE A DATA SURELY INCLUDE A DATA
DICTIONARY.DICTIONARY.
IT PROVIDES DATABASE IT PROVIDES DATABASE
ADMINISTRATORS AND OTHER ADMINISTRATORS AND OTHER
USERS, EASY ACCESS TO TYPE OF USERS, EASY ACCESS TO TYPE OF
DATA THAT THEY SHOULD EXPECT TO DATA THAT THEY SHOULD EXPECT TO
SEE IN EVERY TABLE, ROW AND SEE IN EVERY TABLE, ROW AND
COLUMN OF DATABASE, WITHOUT COLUMN OF DATABASE, WITHOUT
ACTUALLY ACCESSING THE ACTUALLY ACCESSING THE
DATABASEDATABASE

5. NECESSITY OF A DATA NECESSITY OF A DATA
DICTIONARY.DICTIONARY.
SINCE DATABASE IS MEANT TO BE SINCE DATABASE IS MEANT TO BE
BUILT AND USED BY MULTIPLE BUILT AND USED BY MULTIPLE
USERS, MAKING SURE THAT USERS, MAKING SURE THAT
EVERYONE IS AWARE OF WHAT EVERYONE IS AWARE OF WHAT
TYPES OF DATA EACH FIELD WILL TYPES OF DATA EACH FIELD WILL
ACCEPT BECOMES A CHALLENGE.ACCEPT BECOMES A CHALLENGE.
SO A DATA DICTIONARY IS EFFECTIVE SO A DATA DICTIONARY IS EFFECTIVE
ADD ON TO ENSURE DATA ADD ON TO ENSURE DATA
CONSISTENCY.CONSISTENCY.

6. A dAtA dIctIonAry Is :A dAtA dIctIonAry Is :
A tool for recording and processing A tool for recording and processing
information (metadata)about the data that an information (metadata)about the data that an
organisation uses.organisation uses.
 A central catalogue for metadata.A central catalogue for metadata.
 Can be integrated within the DBMS or be Can be integrated within the DBMS or be
separate.separate.
 May be referenced during system design, May be referenced during system design,
programming, and by actively-executing programming, and by actively-executing
programs.programs.

7. MetA dAtA:MetA dAtA:
Metadata (meta content) is defined as data Metadata (meta content) is defined as data
providing information about one or more providing information about one or more
aspects of the data, such as:aspects of the data, such as:
Means of creation of the dataMeans of creation of the data
Purpose of the dataPurpose of the data
Time and date of creationTime and date of creation
Creator or author of dataCreator or author of data
Placement on a computer network where the Placement on a computer network where the
data was createddata was created
Standards usedStandards used
The basic informationThe basic information

8. FORMAT FOR DATA FORMAT FOR DATA
DICTIONARYDICTIONARY
THERE EXISTS NO STANDARD THERE EXISTS NO STANDARD
FORMAT FOR CREATING A DATA FORMAT FOR CREATING A DATA
DICTIONARY.DICTIONARY.
META-DATA DIFFERS FROM TABLE TO META-DATA DIFFERS FROM TABLE TO
TABLE.TABLE.
THE ONLY PREREQUISITE FOR A THE ONLY PREREQUISITE FOR A
DATA DICTIONARY IS THAT IT SHOULD DATA DICTIONARY IS THAT IT SHOULD
BE EASILY SEARCHABLE.BE EASILY SEARCHABLE.

9. STORAGESTORAGE
ONLY APPLICABLE RULE FOR ONLY APPLICABLE RULE FOR
STORAGE IS THAT IT SHOULD BE AT STORAGE IS THAT IT SHOULD BE AT
CONVENIENT LOCATION THAT IS CONVENIENT LOCATION THAT IS
EASILY ACCESSIBLE TO ALL USERS EASILY ACCESSIBLE TO ALL USERS
OF DATABASE.OF DATABASE.
TYPES OF FILES USED TO STORE TYPES OF FILES USED TO STORE
DATA IN DATA DICTIONARY RANGE DATA IN DATA DICTIONARY RANGE
FROM TEXT FILES, XML FILES, FROM TEXT FILES, XML FILES,
SPREADSHEETS, AN ADDITIONAL SPREADSHEETS, AN ADDITIONAL
TABLE IN DATA BASE ITSELF ETC.TABLE IN DATA BASE ITSELF ETC.

10. structure of A dd:structure of A dd:
DD can be DD can be integratedintegrated with the DBMS or with the DBMS or
stand-alonestand-alone
Relational systems all have some form of Relational systems all have some form of
integrated DD (e.g., Oracle)integrated DD (e.g., Oracle)
Integrated DD is usually active, meaning it Integrated DD is usually active, meaning it
is automatically updated to reflect changes is automatically updated to reflect changes
in the databasein the database
A stand-alone DD is not directly linked to A stand-alone DD is not directly linked to
the database and must be updated the database and must be updated
manuallymanually

11. ADVANTAGES OF DATA ADVANTAGES OF DATA
DICTIONARYDICTIONARY
IT EXUDES CLARITY ON THE REST OF IT EXUDES CLARITY ON THE REST OF
THE DATABASE DOCUMENTATION.THE DATABASE DOCUMENTATION.
WHEN A NEW USER IS INTRODUCED WHEN A NEW USER IS INTRODUCED
TO THE SYSTEM, IDENTIFYING TABLE TO THE SYSTEM, IDENTIFYING TABLE
STRUCTURE AND TYPES BECOMES STRUCTURE AND TYPES BECOMES
SIMPLE.SIMPLE.

12. dIsAdvAntAges:dIsAdvAntAges:
A DDS is a useful management tool, but at a price.A DDS is a useful management tool, but at a price.
 The DDS ’project’ may itself take two or three years.The DDS ’project’ may itself take two or three years.
 It needs careful planning, defining the exact It needs careful planning, defining the exact
requirementsrequirements
designing its contents, testing, implementation anddesigning its contents, testing, implementation and
evaluation.evaluation.
 The cost of a DDS includes not only the initial price of itsThe cost of a DDS includes not only the initial price of its
installation and any hardware requirements, but also the installation and any hardware requirements, but also the
costcost
of collecting the information entering it into the DDS, of collecting the information entering it into the DDS,
keepingkeeping
it up-to-date and enforcing standards.it up-to-date and enforcing standards.
 The use of a DDS requires management commitment, The use of a DDS requires management commitment,
whichwhich
is not easy to achieve, particularly where the benefits areis not easy to achieve, particularly where the benefits are
intangible and long term.intangible and long term.