A data dictionary is a “virtual database” containing metadata (data about data). Data dictionary holds information about the database and the data that it stores.
4. What is a data dictionary?
◇It is an integral part of a database.
◇It holds information about the
database and the data that it stores.
◇A data dictionary is a “virtual
database” containing metadata
(data about data).
5. META DATA
Metadata is defined as data providing
information about one or more aspects of the
data, such as:
◇Time and date of creation.
◇Authorization of the data.
◇Attribute size.
◇Purpose of the data.
6. “
It is where the systems analyst goes to
define or look up information about
entities, attributes and relationships on
the ERD (Entity Relationship Design).
7.
8. Data Dictionary provides information
about database
◇ Table
◇ Indexes
◇ Columns
◇ Constrains
◇ Relationship to other variables
◇ Precision of data
◇ Variable format
◇ Packages
◇ Data type
◇ And more
9. BIG Importance
◇ Avoid duplication.
◇ Make maintenance
straightforward.
◇ To locate the error in the
system.
◇ And more.
10. Why Data Dictionary?
Authorization
Report
Easy
Searchable
Catalogue
Record what data belongs to
whom.
Provides quick report on the data and
hence making the data management easy.
Easy to search data in huge database.
A central catalogue for metadata.
DBA can easily able to track any chaos
in the database.
11. Relational
systems all have
some form of
integrated data
dictionary (e.g.
Oracle)
Structure of Data
Dictionary
It can be
integrated with
the DBMS or
stand-alone.
It automatically
reflect the
changes in the
database.
12. Disadvantages of
Data Dictionary?
Creating a new data
dictionary is a very big
task. It will take years to
create one.
The cost of data
dictionary will be bit
high as it includes its
initial build and
hardware charges as
well as cost of
maintenance.
It needs careful
planning, defining the
exact requirements
designing its contents,
testing,
implementation and
evaluation.
Requires management
commitment, which
is not easy to achieve,
particularly where the
benefits are
intangible and long term.
13. Viewing Information in the
Data Dictionary
◇ Although you are not allowed to modify the dictionary
yourself, you can DESCRIBE and SELECT from Dictionary
tables.
◇ For example, to see information about all the tables that you
have privileges to use:
◇ The output from this shows that many columns of data are
held about each table. You decide you only want to see the
name and owner, so you enter:
DESCRIBE ALL_TABLES
SELECT table_name, owner FROM ALL_TABLES;
14. Conclusions
The ideal data dictionary is automated,
interactive, online and evolutionary.
The data dictionary should be tied into a
number of systems programs so that
when an item is updated or deleted from
the data dictionary, it is automatically
updated or deleted from the data base.
The data dictionary may also be used to
create screens, reports and forms.
