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2： metadata, schema, and catalog

Metadata, Schema, and Catalog are very common names in database, so what are the meaning of them?


1: Metadata

In short, metadata is the data about other data.

Metadata is defined as the data providing information about one or more aspects of the data; it is used to summarize basic information about data which can make tracking and working with specific data easier.


2: Schema

Schemas are analogous to directories at the operating system level, except that schemas cannot be nested.

There are several reasons why one might want to use schemas:

  • To allow many users to use one database without interfering with each other.
  • To organize database objects into logical groups to make them more manageable.
  • Third-party applications can be put into separate schemas so they do not collide with the names of other objects.


3: Catalog

The system catalogs are the place where a relational database management system stores schema metadata, such as information about tables and columns, and internal bookkeeping information.


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