Data Dictionary

Hello!I am Vishal Anand

Data DictionaryLet’s start with the first set of slides

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).

META DATAMetadata 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.

“It is where the systems analyst goes to define or look up information about entities, attributes and relationships on the ERD (Entity Relationship Design).

Data Dictionary provides information about database◇ Table◇ Indexes◇ Columns◇ Constrains◇ Relationship to other variables◇ Precision of data◇ Variable format◇ Packages◇ Data type◇ And more

BIG Importance◇ Avoid duplication.◇ Make maintenance

straightforward.◇ To locate the error in the

system.◇ And more.

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.

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.

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, whichis not easy to achieve, particularly where the benefits areintangible and long term.

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;

ConclusionsThe 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.

Thanks!Any questions?