原文：What's the Difference Between Metadata and Data Dictionary? (reference.com)
Metadata is also known as the System Catalog. It describes how, when and by whom certain data was collected as well as the format and context of the data. A data dictionary is a centralized collection of data information.
Metadata is used by developers to create programs, procedures, controls and queries to manipulate and manage the data in a database. It is connected with the database management system software and is accessed by the software’s data definition language and data manipulation language compilers. There are two types of metadata: structural metadata, which conveys how the data is set up and stored, and descriptive metadata, which describes the data itself.
A data dictionary is a structure that stores metadata. It is used to control database operations, integrity and accuracy. It also holds the number of files available in a database, the number of records of every file and information about the fields.
There are two types of data dictionaries: passive data dictionaries and active data dictionaries. A passive or non-integrated data dictionary is utilized by users, administrators and designers but not by the database management system software. An active or integrated data dictionary is managed automatically by the database management system software.