A data dictionary in DBMS (Database Management System) is a collection of names, definitions, and attributes about data elements that are being used or captured in a database, information system, or part of a research project. It contains metadata, which is data about the database, such as what is in the database, who is allowed to access it, where is the database physically stored, etc.. The data dictionary provides information about the relationships between multiple tables in a database, helps to organize data, and prevents data redundancy. It describes the meanings and purposes of data elements within the context of a project, and provides guidance on interpretation, accepted meanings, and representation. The metadata included in a data dictionary can assist in defining the scope and characteristics of data elements, as well as the rules for their usage and application. The data dictionary also provides structured analysis and design tools by enforcing the use of data standards. Data standards are the set of rules that govern the way data is collected, recorded, and represented. Using a data dictionary helps to define naming conventions that are used in a model. The different types of data dictionary are Active Data Dictionary and Stand Alone Data Dictionary.