Meta data :- Metadata is data about the data or documentation about the information which is required by the users. In data warehousing, metadata is one of the essential aspects.

Metadata includes the following:

• The location and descriptions of warehouse systems and components.

• Names, definitions, structures, and content of data-warehouse and end-users views.

• Identification of authoritative data sources.

• Integration and transformation rules used to populate data.

• Integration and transformation rules used to deliver information to end-user analytical tools.

Uses of Metadata :-

• Metadata acts as a directory.

• This directory helps the decision support system to locate the contents of the data warehouse.

• Metadata helps in decision support system for mapping of data when data is transformed from operational environment to data warehouse environment.

• Metadata helps in summarization between current detailed data and highly summarized data.

• Metadata also helps in summarization between lightly detailed data and highly summarized data.

• Metadata is used for query tools.

• Metadata is used in extraction and cleansing tools.

• Metadata is used in reporting tools.

• Metadata is used in transformation tools.

• Metadata plays an important role in loading functions.

Types of Metadata : - Metadata can be broadly categorized into three categories −

1. Business Metadata − It has the data ownership information, business definition, and changing policies.

2. Technical Metadata − It includes database system names, table and column names and sizes, data types and allowed values. Technical metadata also includes structural information such as primary and foreign key attributes and indices.

3. Operational Metadata − It includes currency of data and data lineage. Currency of data means whether the data is active, archived, or purged. Lineage of data means the history of data migrated and transformation applied on it.

Several examples of metadata are :-

• A library catalog may be considered metadata. The directory metadata consists of several predefined components representing specific attributes of a resource, and each item can have one or more values. These components could be the name of the author, the name of the document, the publisher's name, the publication date, and the methods to which it belongs.

• The table of content and the index in a book may be treated metadata for the book.

• Suppose we say that a data item about a person is 80. This must be defined by noting that it is the person's weight and the unit is kilograms. Therefore, (weight, kilograms) is the metadata about the data is 80.

• Another examples of metadata are data about the tables and figures in a report like this book. A table (which is a record) has a name (e.g., table titles), and there are column names of the tables that may be treated metadata. The figures also have titles or names.