Here are the top 50 commonly asked questions in DBMS interviews. Whether you’re just starting your preparation or need a quick refresher, these questions and answers will help you tackle your interview with confidence.
Basic DBMS Interview Questions with Answers
1. What is database management system?
Database management system (DBMS) is a general – purpose software program responsible for storage, retrieval, definition, and organization of data in a database. This software allows building, defining, working, and sharing databases for multiple application programs.
2. What is the purpose of database management system?
The main purpose of database management system is large storage of data, simplified access, and modification. It should be able to eliminate data redundancy and irregularity, and make sure that only authorized users are allowed access.
3. What is an instance in DBMS?
Instance can be defined as a glimpse or snapshot of the data in a database at any given instant of time. The way the database is viewed at the current instant may vary from how it was viewed few minutes ago as there may be modifications made on it. Instance allows us to see those modifications.
4. Why is a storage manager needed in DBMS?
Database is used to store large amount of data for processing. Hence, a large storage space is needed, and a storage manager is responsible for storing, retrieving, updating, and managing the data in this large storage space. It acts as an interface between the data stored and application programs requiring access to it.
5. What is the role of query processor in DBMS?
The data stored in database is used by various application programs. A query processer is necessary to facilitate the faster processing of the user’s queries which will simplify the process of access to data in the database.
6. What is index in DBMS?
Indices are used to provide faster access to the data in the database. It provides quick data accesses by reducing the number of disk accesses required for every query that is processed.
7. What is an entity in DBMS?
Entity is an object or a thing from the real world which is distinct from other objects. An entity has a set of properties which describe its individuality. An employee in an organization is an entity.
8. What is an attribute domain in DBMS?
Attribute domain is defined as the pre – defined value or scope of an attribute in relation. An attribute may have constraint that it cannot contain NULL values, or it should contain unique values. These unique and not NULL constraints are the attribute domain of that particular attribute.
9. What is an entity set in DBMS?
Entity set is a collection of entities of a similar entity type i.e., possess similar attributes or characteristics. All the faculties working in an educational institution may be defined under a single entity set.
10. What is an attribute in DBMS?
Attribute is defined as the properties which distinguish one entity set from another. They are the descriptive characteristics of each member in an entity set. The attributes of the ‘instructor’ entity set may be instructor’s ID, name, department name, salary, age and so on.
11. What is a relationship in DBMS?
Relationship is used to represent the connection or association between different entities. An instructor may be related to a student as a mentor. Relationships are represented using diamond symbol in the E – R diagram.
12. Why is relational model the most popular data model in DBMS?
Relational model allows storage of data in tables called relations. Storage of data in relations allow easier modification, maintenance, and management. Any modification can be done by changing the values in the table and relationships can be easily interpreted using tables. This also enables easy implementation of SQL queries.
13. What is the meaning of value of an attribute in DBMS?
Entities are described by a set of attributes and each entity has a value for each of its attributes which may or may not be unique. An instructor has an attribute ID whose value is 10000.
14. What are the two entries in the table maintained for indexing in DBMS?
Faster access using indexing is achieved with a help of a table containing two columns. The first column of the table holds the primary key or the candidate key of the respective table whereas as the second columns contains a set of pointers to indicate the locations where the specific key values are stored in the disk block.
15. What is the meaning of degree of a relationship set in DBMS?
Degree of a relationship set is the number of entity sets associating or participating in the relationship set. If the relationship set associates two entity sets, it is termed as a binary relationship.
16. What is an intangible entity in DBMS?
Intangible entity is referred to a real – world object which exists only logically and there is no physical existence or trace of it. Bank account is an example of an intangible entity as it only has a logical existence in the real world.
17. What is a weak entity set?
Usually, each entity set has a unique attribute or set of attributes forming a primary key. A weak entity set is an entity set incapable of forming a primary key because of insufficient attributes to create a primary key.
18. What is a strong entity set?
A strong entity set is an entity set which has the sufficient attribute or set of attributes to form a primary key which uniquely recognizes each record in a relation.
19. What are the properties of a primary key in DBMS?
A primary key is responsible for unique identification of records in a table. Hence, each record must only contain a unique value for the attribute or attributes acting as primary key. Further, it cannot contain NULL values as well.
20. What is an identifying relationship in DBMS?
A weak entity set is meant to be meaningful only when it is associated with a strong entity set called identifying or owner entity set. The relationship connecting the weak entity set with its owner entity set is called an identifying relationship.
Intermediate DBMS Interview Questions with Answers
21. What is data?
Data can be defined as facts which are unsystematic, raw, and disorganized but have implicit meaning. Data must be processed to derive the significant information which is being conveyed. Examples of data are age, name, address and so on.
22. What is information?
Information is organized data which has been processed in a meaningful manner. Processed, structured and expressive data is more useful to perform the required tasks.
23. What is a database?
Database is a systematic collection of related data with intrinsic meaning. Databases allow electronic storage of information which makes updation, manipulation, deletion, and insertion of data much easier.
24. What is the meaning of the term “defining a database”?
Defining a database refers to mentioning the data types, design for structuring the data and constraints to be put on the data stored in the database.
25. What is the meaning of the term “constructing a database”?
Constructing a database refers to storage of data in the respective physical storage medium that is controlled by the database management system.
26. What is the meaning of the term “manipulating a database”?
Manipulating a database refers to modification of stored data i.e., updating, deleting or inserting data, retrieval of specific data and querying to generate reports on the data in the database.
27. What is database schema?
Database schema is the overall logical design of how data will be stored in the database. It describes the entities used to represent the data and depicts the relationship among these entities by means schema diagrams.
28. What is data independence?
Data independence is the capacity to reflect changes in the database design or schema at one particular level of a database system without needing any changes in the schema at the other levels of design.
29. What is data abstraction?
Data abstraction is defined as the portrayal of only the essential features while suppressing the unwanted details with respect to data organization and storage. The users don’t need information of how data is actually stored or how the operations are performed on data, hence DBMS provides only the conceptual illustration of the database.
30. What is physical database schema?
Physical database schema pertains to the actual storage of data in the physical storage medium. It depicts database design at the physical level where the data is kept in secondary storage in the form of files, indices and so on.
31. What is logical database schema?
Logical database schema relates to design of database at the logical level. It defines the representation of data in tables and views and specifies the integrity constraints applied on the data.
32. What is sub – schema?
Sub – schema is referred to the different schemas of the database at the view level of the database design. It depicts the different views of the data stored in the database.
33. What is a table in a database?
Table is a structure used to represent the data in a database as a combination of rows and columns containing some values. Table is also referred to as a relation and it is the most important component of the database.
34. What is a record in a database?
Record also referred to as a row or tuple is a collection of related data with each row having a similar structure. A record contains unique values for different fields of a single entity.
35. What is a field in a database?
Field also referred to a column or attribute is used to identify the different classes of data in a database. Each field holds data of a particular type like text, numbers, alphanumeric and so on.
36. What are data files?
Data files are used to store the entire database itself. It acts as a repository which stores all the data relating to the objects represented in the schema of a database.
37. What is data dictionary?
Data dictionary is used to store the metadata which contains the description of the structure of the database. It contains the names of the relations and their schemas, details of data stored, the security and integrity constraints applied, how and where the data is stored in physical medium, and who has access to the which data.
38. What is DDL?
Data Definition Language (DDL) is mainly used for defining the database, designing the schema of the database and to create and alter the structure of the objects in the database before the actual storage of data.
39. What is DML?
Data Manipulation Language (DML) is mainly used for manipulating or working on the data stored in the database according to the user’s queries. The user can insert, delete, and update specific data using DML.
40. What is a data model?
Data model is a structure used to define how data will be stored, accessed, manipulated, and shared in a database management system. It specifies a set of operations to store, retrieve, update, and delete data and also depicts the relationship between the different objects in the database.
41. What is object – oriented data model?
Object – oriented data model uses a structure called as object to represent both data and the relationships among them. The objects are connected or related to each other by means of links.
42. What is object relational data model?
Object – relational data model combines the features of object – oriented data model as well as relational model. It incorporates both objects and tabular structure for data storage.
43. What is the difference between total and partial participation between entity sets?
Total participation indicates that all the entity sets associated with a relationship are involved in the relationship while partial participation indicates that not all the connected entity sets are participating in the relationship.
44. What is Enhanced E – R Model?
Enhanced E – R model also called as Extended E – R model, is an extension of the existing E – R model which supports more complex databases. In addition to supporting the functionalities of simple E – R model, it has provisions to support sub – classes, super – classes, specialization, generalization, aggregation, and inheritance.
45. What is overlapping specialization?
Overlapping specialization is a type of specialization in which an entity from the super class may belong to more than one sub – classes i.e., it is said to belong to multiple specialized entity sets.
46. What is disjoint specialization?
Disjoint specialization is a type of specialization in which an entity from the super class may belong to at most one sub – class i.e., it is said to have only one specialization.
47. What is generalization?
Generalization is the process of defining a generalized entity by combining multiple lower – level entity types based on one or more common distinguishing features. It employs a bottom – up approach.
48. What is aggregation?
Aggregation is the process by which relationships can be regarded as higher – level entities. It allows the relation between two or more entities to be treated as a single entity.
49. What is a relational database?
Relational database refers to the storage of data in the form of relations with unique names. The data in the database is organized in the form of tables with rows and columns which hold information about the real – world objects to be depicted in the database.
50. What is attribute inheritance?
Attribute inheritance is the application of distinctive attributes of higher – level entities to the lower – level entities i.e., properties of higher – level entities are inherited by the lower – level entities. For example a student and an instructor both inherit attributes of the entity ‘Person’.
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