What is a Data Dictionary?

A Data Dictionary is a Record or a set of documents that includes a Database's Metadata. The statistics dictionary contains records approximately different items in the database, which includes inFormation ownership, information Relationships to other items, and different statistics.

The statistics dictionary is a important factor of any Relational Database. It gives extra statistics about Relationships between extraordinary database Tables, enables to arRange records in a neat and without difficulty searchable manner, and forestalls Data Redundancy troubles.

Ironically, due to its importance, it\'s miles invisible to most database users. Typically, best database directors engage with the facts dictionary.

A data dictionary is likewise referred to as a MetaData Repository.

What Does Data Dictionary Mean?

A Data Dictionary carries facts about Attributes or Fields of a positive Data Set. In a relational database, the metadata inside the statistics dictionary includes the subsequent:

• Names of all tables within the database and their proprietors.

• Names of all Indexes and the columns to which the tables in those indexes relate.

• Constraints described on tables, along with Primary Keys, overseas-key relationships to other tables, and now Not-Null Constraints.

• Additional physical statistics approximately the tables such as their Storage area, storage technique, and so on.

For example, a Business bank's database containing facts approximately customers may have attributes for Client name, beginning date, road address, monetary financial savings, account and credit score card Variety, loans, and many others.

Each Characteristic occupies a row in a Spreadsheet, even as various columns provide extra factors that describe that characteristic (whether it’s non-obligatory or required for a report, the sort of information, its area, and so on.).

A statistics dictionary might appear like the only underneath:

For most relational database management structures (RDBMS), the database management Device Software desires the facts dictionary to get admission to the statistics inside a database. For example, the Oracle DB software has to examine and write to an Oracle DB. However, it may most effective do that thru the statistics dictionary created for that specific database.

For example, following the above bank's database Instance, the administrator wants to determine which table holds statistics approximately loans. Making an educated guess that the table maximum probable has the word \"LOAN\" in it, he would difficulty the following Query on the statistics dictionary (the primary query is for an Oracle DB, whilst the second is for an SQL Server DB):

• SELECT * FROM DBA_TABLES WHERE TABLE_NAME LIKE '%LOAN%'

• SELECT * FROM SYSObjectS WHERE TYPE='U' AND NAME LIKE '%LOAN%'

A records dictionary can be both active or passive. It may additionally take place that the structure of the database needs to be cHanged, including to add new attributes or to take away some Obsolete ones. If the ones adjustments are up to date mechanically inside the records dictionary through the database control dictionary, then the statistics dictionary is an energetic one.

Conversely, if the database supervisor maintains the statistics dictionary as a separate Entity that has to be UPDATEd manually, it\'s miles referred to as a passive facts dictionary. Other than requiring extra paintings to be synced, passive information dictionaries are vulnerable to mistakes whilst statistics in the database and dictionary do not fit anymore.