DBMS QUESTIONS

1. Define query language?

A query is a statement requesting the retrieval of information. The portion of

DML that involves information retrieval is called a query language.

2. Write short notes on Schema diagram.

A database schema along with primary key and foreign key dependencies can be

depicted pictorially by schema diagram. Each relation appears as a box with

attributes listed inside it and the relation name above it.

3. What is foreign key?

A relation schema r1 derived from an ER schema may include among its

attributes the primary key of another relation schema r2.this attribute is called a foreign

key from r1 referencing r2.

4. What is a SELECT operation?

The select operation selects tuples that satisfy a given predicate. We use the

lowercase letter s to denote selection.

5. Give the levels of data abstraction?

a) Physical level

b) logical level

c) view level

6. Define instance and schema?

Instance: Collection of data stored in the data base at a particular moment is

called an Instance of the database.

Schema: The overall design of the data base is called the data base schema.

7. Define the terms 1) physical schema 2) logical schema.

Physical schema: The physical schema describes the database design at the

physical level, which is the lowest level of abstraction describing how the data are

actually stored.

Logical schema: The logical schema describes the database design at the logical

level, which describes what data are stored in the database and what relationship exists

among the data.

8. What is conceptual schema?

The schemas at the view level are called subschemas that describe different views

of the database.

9. Define data model?

A data model is a collection of conceptual tools for describing data, data

relationships, data semantics and consistency constraints.

10. What is storage manager?

A storage manager is a program module that provides the interface between the

low level data stored in a database and the application programs and queries submitted to

the system.

11. What are the components of storage manager?

The storage manager components include

a) Authorization and integrity manager

b) Transaction manager

c) File manager

d) Buffer manager

12. What is the purpose of storage manager?

The storage manager is responsible for the following

a) Interaction with he file manager

b) Translation of DML commands in to low level file system commands

c) Storing, retrieving and updating data in the database

13. List the data structures implemented by the storage manager.

The storage manager implements the following data structure

a) Data files

b) Data dictionary

c) indices

14. What is a data dictionary?

A data dictionary is a data structure which stores meta data about the structure of

the database ie. the schema of the database.

15. What is an entity relationship model?

The entity relationship model is a collection of basic objects called entities and

relationship among those objects. An entity is a thing or object in the real world that is

distinguishable from other objects.

16. What are attributes? Give examples.

An entity is represented by a set of attributes. Attributes are descriptive properties

possessed by each member of an entity set.

Example: possible attributes of customer entity are customer name, customer id,

customer street, customer city.

17. What is relationship? Give examples

A relationship is an association among several entities.

Example: A depositor relationship associates a customer with each account that

he/she has.

18. Define the terms

i) Entity set

ii) Relationship set

Entity set: The set of all entities of the same type is termed as an entity set.

Relationship set: The set of all relationships of the same type is termed as a

relationship set.

19. Define single valued and multivalued attributes.

Single valued attributes: attributes with a single value for a particular entity are

called single valued attributes.

Multivalued attributes: Attributes with a set of value for a particular entity are

called multivalued attributes.

20. What are stored and derived attributes?

Stored attributes: The attributes stored in a data base are called stored attributes.

Derived attributes: The attributes that are derived from the stored attributes are

called derived attributes.

21. What are composite attributes?

Composite attributes can be divided in to sub parts.

22. Define null values.

In some cases a particular entity may not have an applicable value for an attribute

or if we do not know the value of an attribute for a particular entity. In these cases null

value is used.

23. Define the terms

i) Entity type

ii) Entity set

Entity type: An entity type defines a collection of entities that have the same

attributes. 

Entity set: The set of all entities of the same type is termed as an entity set.

24. What is meant by the degree of relationship set?

The degree of relationship type is the number of participating entity types.

25. Define the terms

i) Key attribute

ii) Value set

Key attribute: An entity type usually has an attribute whose values are distinct

from each individual entity in the collection. Such an attribute is called a key attribute.

Value set: Each simple attribute of an entity type is associated with a value set

that specifies the set of values that may be assigned to that attribute for each individual

entity.

26. Define weak and strong entity sets?

Weak entity set: entity set that do not have key attribute of their own are called

weak entity sets.

Strong entity set: Entity set that has a primary key is termed a strong entity set.

27. What does the cardinality ratio specify?

Mapping cardinalities or cardinality ratios express the number of entities to which

another entity can be associated. Mapping cardinalities must be one of the

following:

• One to one

• One to many

• Many to one

• Many to many

28. Explain the two types of participation constraint.

• Total: The participation of an entity set E in a relationship set R is said to

be total if every entity in E participates in at least one relationship in R.

• Partial: if only some entities in E participate in relationships in R, the

participation of entity set E in relationship R is said to be partial.

29. Define the terms

i) DDL

ii) DML

DDL: Data base schema is specified by a set of definitions expressed by a special

language called a data definition language.

DML: A data manipulation language is a language that enables users to access or

manipulate data as organized by the appropriate data model.

30. Write short notes on relational model

The relational model uses a collection of tables to represent both data and the

relationships among those data. The relational model is an example of a record

based model.

31. Define tuple and attribute

• Attributes: column headers

• Tuple: Row

32. Define the term relation.

Relation is a subset of a Cartesian product of list domains.

33. Define tuple variable

Tuple variable is a variable whose domain is the set of all tuples.

34. Define the term Domain.

For each attribute there is a set of permitted values called the domain of that

attribute.

35. What is a candidate key?

Minimal super keys are called candidate keys.

36. What is a primary key?

Primary key is chosen by the database designer as the principal means of

identifying an entity in the entity set.

37. What is a super key?

A super key is a set of one or more attributes that collectively allows us to

identify uniquely an entity in the entity set.

38. Define- relational algebra.

The relational algebra is a procedural query language. It consists of a set of

operations that take one or two relation as input and produce a new relation as

output.