Introduction to Data Dictionaries
The Data Dictionary is like any other subject dictionary which keeps a record of the objects in the database. These objects are also known as “Metadata” in software technology terms. These objects primarily are records related to data ownership, the relationship of data with other objects, and other data structure of the objects. Now just imagine a database without information of the database itself, once made can lead you to lose the data indefinitely as we have no information about the database stored anywhere and ironically this makes an inevitable part of a database.
What are Data Dictionaries?
Now let us formally look into what it is and let us have a formal definition of the same so that it can well communicate within the group. In the IBM Dictionary of computing, this is defined as “a repository which is centralized and contains information of the data in the database such that the meaning, relationship, source of data, where it will be used and the format is clearly mentioned or specified”. This term is changed interchangeably with many other definitions and the best definition can be any one of these below of the definition in the IBM dictionary.
- A document that describes the database or its collection.
- A part of DBMS which is required for determining the structure.
- A middleware that helps in extending the inbuilt data dictionary of DBMS.
It has the following information about the database, and they are:
Database table names and their schemas: As the name suggests the name of the table which stores the data and the schema which it follows is stored here. The schema for example might be the date of birth of an employee in an employee database should have date type format. The owners of the database and their security constraints are stored in the dictionary. The place of storage of the table, the physical information of the tables, and the aliases of the data item is stored in the dictionary. Primary key attributes, information about the foreign key, etc. which constitutes the table constraints. Constraints like the range of values are also stored in the data dictionary, for example, date of birth can’t be greater than today’s date. Finally, the views of the database which are visible are also stored here.
Types of Data Dictionary
Now let us talk about different types of it :
1. Active Data dictionary
A huge responsibility of the database management system is to make sure that the change in the structure of the database should immediately be reflected in the data dictionary. It follow this immediate update methodology is known as an active data dictionary as they are self-updating.
2. Passive data dictionary
These types of dictionaries are not that useful or easy to handle like an active data dictionary. Every time a database is modified, one has to manually update the data dictionary to match the database. This dictionary is maintained separately from the database. Now you must be wondering that if the database is not automatically updated, what’s the use then? Well the answer is that along with the disadvantage of automatic update there are a lot of advantages like passive data can be used for storing the metadata as a central repository as they are not tied to a database, unlike active data dictionary. Hence, can be used for multiple databases that are virtually the same simultaneously. Also, we can have additional metadata which is lacking an inactive data dictionary. Lastly, the job is easy when you get a friendly UI with search capability in a passive data dictionary.
There are some operators who are used in it and let us look at them so that, this topic is even more realistic to the working world!
- a = x + y: This means that x, y data elements are included in “a”.
- a = [x/y]: This means that either element of x or y are included in “a”.
- a = x: This means that optimal elements of x are included in “a”.
- a = b[x]: This means that b or more occurrences of elements of x are included in “a”.
- a = [x]b: This is just the opposite of the earlier, i.e. b or fewer occurrences of elements of x are included in “a”.
- a = b[x]c: This is a combination of the earlier two, i.e. b or more occurrences, and c or fewer occurrences of elements of x are included in “a”.
Uses of Data Dictionaries
Now, let us look at the uses of it in the real-world and some advantages it brings along in the next few sections.
This comes in handy on various instances and they are:
Users can create an ordered listing of all data items and help to create quick reports on the data hence making the data management easy. It helps DDL in searching for an object when a DDL is fired on database objects. It helps only authorized users to see and view the table, hence acts as a security wall. It is used for creating software design and test cases.
Advantages of Data Dictionaries
Now we can easily mediate through the advantages data dictionaries brings along, so in this section let us look at them in pointers so that this may serve a reference in adjudging when you look forward to using data dictionary:
1. The attributes of the columns are provided here as an organized and comprehensive list. This will go a long way in understanding the data for a database administrator when he takes it over from another person.
2. The built of the data dictionary is such that the provision of easy searching is available.
3. Multiple programs can utilize a data dictionary for providing reporting and documentation purposes.
4. It helps in maintaining data is such a way that we don’t encounter redundant data.
5. It makes sure that the structure of the data required is simplified in the process.
6. The storage of metadata helps in maintaining high data integrity over databases.
7. It comes in handy when a design process in software starts and evaluates the test cases written for testing.
8. The relation information across different tables are captured as a part of the process of creation of data dictionaries.
In this article, we have learned how data dictionary is an inevitable part of DBMS and what fundamentals revolve around data dictionary. It is only the data dictionary one can refer to or consult to understand where a data item would fit in the structure of DBMS. data item gets its real-world meaning.
This is a guide to Data Dictionaries. Here we discuss an introduction to Data Dictionaries, what it is, different types, uses, and respective advantages. You can also go through our other related articles to learn more –