CHAPTER -13
(DATA DICTIONARY)
DATA DICTIONARY :- A data dictionary contains meta data. Data about the database, It contains information such as what is in the database, who is allowed to access it, where is the database physically stored etc. It play an important role in building a database.
Table 1. This is a normal data stored flowchart.
Client -id | Client -Name | Password | Contact No | Email |
1. | Shailesh | 010101010 | 777-888-999 | |
2. | Sudhir | 101010101 | 111-222-333 | |
3. | Gulab | 123456789 | 444-555-666 | |
4. | Abhishek | 789456123 | 777-888-999 |
Table 2. Example of Data Dictionary.
Filed Name | Data Type | Filed Length | Constrains | Description |
Client id | Number | 10 | Primary key | Client id auto generated |
Client Name | varchar | 20 | Not null | Name of client |
Password | varchar | 30 | Not null | Login Password |
Contact no | number | 10 | Not null | Contact of client |
Email | varchar | 40 | Not null | Client email |
The data dictionary in general contains information about the following:-
1. Name of cull table in the database
2. Name of each field in the table of the database
3. Constraints define on table
4. Physical information about tables like their storage location, storage method show on figure /Table 2
5. The user of the database normally don’t interest with the data dictionary, It is only handed only by the database administrator
6. A data dictionary is also called a meta data reposting
Types of Data Dictionary :- There are two types
Active and Passive
Active :- It may happen that the structure of the database has to be changed like that adding new attributes or removing older ones, if those changes are update automatically in the Data Dictionary by the DBMS, then the data dictionary is an active one. It is also known as integrated data dictionary.
Passive :- When the DMBS maintains the data dictionary separately and it has to be uploaded manually then the data dictionary is an passive one. It is also known non- integrated data dictionary. In this case there is a choose of mismatch with the database objects and the data dictionary.
Advantage of Data Dictionary :-
It gives the well Structured and clear information about the database, one can analyse the requirements any redundancy like duplicated columns, tables, row etc.
It is very helpful for the administrator or any new PBA to understand the database since it has all the information about the database PBA can easily able to track any choose in the database. Since database is a very huge, and will have lots of table, views constraints, index etc. It is valuable references in any organization because it provides documents.
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