What is a Data Dictionary?

Question. What is a Data Dictionary?
Answer : Data Dictionary provides a metadata about the data explaining the meaning of each and every field, data types of the field, sample values etc. Understanding the business context of fields in the data helps one to use appropriate features in the model. Data Dictionaries play an important role in understanding the data before we dive deep into it. In order to get started with Modelling, it is very important to understand the data.


Q. डेटा डिक्शनरी क्या है?

Answer – डेटा डिक्शनरी प्रत्येक फ़ील्ड के अर्थ, फ़ील्ड के डेटा प्रकार, नमूना मान आदि की व्याख्या करने वाले डेटा के बारे में एक मेटाडेटा प्रदान करता है। डेटा में फ़ील्ड के व्यावसायिक संदर्भ को समझने से मॉडल में उपयुक्त सुविधाओं का उपयोग करने में मदद मिलती है। इससे पहले कि हम इसमें गहराई से उतरें, डेटा डिक्शनरी डेटा को समझने में महत्वपूर्ण भूमिका निभाते हैं। मॉडलिंग के साथ शुरुआत करने के लिए, डेटा को समझना बहुत जरूरी है।


1. Define the term “Data Dictionary”. What is the need for a Data Dictionary?

Answer: A data dictionary is a collection of descriptions of the data objects or items in a data model for the benefit of programmers and others who need to refer to them. Often a data dictionary is a centralized metadata repository.

A first step in analyzing a system of interactive objects is to identify each one and its relationship to other objects. This process is called data modeling and results in a picture of object relationships. After each data object or item is given a descriptive name, its relationship is described, or it becomes part of some structure that implicitly describes relationship. The type of data, such as text or image or binary value, is described, possible predefined default values are listed and a brief textual description is provided. This data collection can be organized for reference into a book called a data dictionary.

When developing programs that use the data model, a data dictionary can be consulted to understand where a data item fits in the structure, what values it may contain and what the data item means in real-world terms. For example, a bank or group of banks could model the data objects involved in consumer banking. They could then provide a data dictionary for a bank’s programmers. The data dictionary would describe each of the data items in its data model for consumer banking, such as “Account holder” and “Available credit.”

Types of data dictionaries

There are two types of data dictionaries. Active and passive data dictionaries differ in level of automatic synchronization.

Active data dictionaries. These are data dictionaries created within the databases they describe automatically reflect any updates or changes in their host databases. This avoids any discrepancies between the data dictionaries and their database structures.

Passive data dictionaries. These are data dictionaries created as new databases — separate from the databases they describe — for the purpose of storing data dictionary information. Passive data dictionaries require an additional step to stay in sync with the databases they describe and must be handled with care to ensure there are no discrepancies.

The need of data dictionary has mainly divided into 3 parts:-

  • Oracle accesses the data dictionary to find information about users, schema objects, and storage structures.
  • Oracle modifies the data dictionary every time that a data definition language (DDL) statement is issued.
  • Any Oracle user can use the data dictionary as a read-only reference for information about the database.

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