Data, Information and Databases

Concept

Three words are used loosely in conversation and precisely in this subject.

A database is an organised collection of related data, stored so it can be retrieved, updated and shared by many users and many programs at once.

The word related is doing real work. A folder holding a photograph, a song and a tax form is a collection of files, not a database. A collection of students, the courses they take and the marks they earn is a database, because the pieces refer to one another.

The four properties every database has

1. It represents some part of the real world. That part is called the mini world or the universe of discourse. When the real world changes, the database must change with it.
2. It is a logically coherent collection. Random data thrown together is not a database.
3. It is designed and populated for a purpose. There is an intended group of users and an intended set of questions it must answer.
4. It is self describing. A database stores not only the data but also a description of its own structure. That description is the metadata, and it is what separates a database from a plain file.

Why the self describing property matters

A PLAIN FILE                      A DATABASE
------------                      ----------
students.txt                      table: students
  87,Meera,2026-03-14               id      INT      not null, key
  91,Ravi,2026-03-14                name    VARCHAR(50)
                                    test_on DATE

The meaning of each column lives     The meaning is stored WITH the data,
only inside the program that         in the catalog, so any program or
reads the file. Change the file      user can discover the structure
and every program breaks.            without reading anyone code.

This is why a database can be shared. Because the structure is stored centrally, a new application can be written against the same data without asking the original programmer what column three meant.

Important terminology

Example

A small college database, shown as its structure rather than its contents. This same example is reused throughout the path, so it is worth reading carefully.

-- Illustration only. This path teaches DBMS concepts;
-- SQL is used here purely to make the structure concrete.

students   ( roll_no, name, dob, dept_code )
courses    ( course_code, title, credits, dept_code )
enrolments ( roll_no, course_code, semester, marks )
departments( dept_code, dept_name, head )

The four tables are related: an enrolment refers to a student and to a course, and both students and courses belong to a department. Remove those references and you no longer have a database, only four lists.

Data versus a database versus a DBMS

Common mistakes

• Calling any file a database. A spreadsheet holds data, but it has no catalog, no controlled sharing and no concurrency control.
• Confusing the database with the DBMS. MySQL is a DBMS. The college records held inside it are the database. Interviewers ask this deliberately.
• Treating data and information as the same word. Data becomes information only when a context makes it answer something.
• Forgetting the self describing property. It is the property most often missed in exams and the one that explains most of the advantages later.

Exam and interview questions

1. Define data, information and knowledge with one example each.
2. List the four properties of a database and explain the self describing property in your own words.
3. What is the difference between a database and a DBMS?
4. Why is a collection of unrelated files not a database?
5. What is a data dictionary and what does it contain?

Practice

1. Write down five data items from your college identity card. Turn each into a sentence of information.
2. Name the mini world of a railway reservation database and list four entities it must store.
3. Explain, in three sentences, what would break if a database stopped storing its own metadata.

Conclusion

Data is raw, information is data in context, and a database is a purposeful, related, self describing collection managed for many users at once. Every advantage discussed in the rest of this phase grows out of those four properties.