Databases(Mid term) Flashcards
What is a schema in Databases
It is a blueprint that defines the structure of the database.
How the table, fields/columns, Relationships, constraints.
What is a database
A Database is a structural organization of information and data.
It has five aspects to it Data storing, retrieving, managing, security, sharing.
What are two aspects of databases.
Data storing, retrieving, managing, security, sharing.
What are the downsides to traditional file storing systems.
1 | Data redundancy
2 | Data access
3 | Data Management
Name the three levels of Databases abstraction.
Physical- Describes how it data is stored
Logical- Explains the relationships between data.
View- Hides certain information from being displayed.
What are the types of Data?
Categories:
a) Attribute Data: Characterizes or describes features.
Example: Eye color, type of car.
b) ‘Open’ Data: Free-form text or responses that don’t fit into predefined categories.
Example: Open-ended survey responses.
c) Ordinal Data: Data with a meaningful order but no fixed intervals between values.
Example: Customer satisfaction ratings (e.g., satisfied, neutral, dissatisfied).
d) Nominal Data: Data without an inherent order or ranking
Example: Types of fruits, categories of books.
What is structured data? Give two example.
Highly organized and easily searchable data is called structured data.
2) Stored in databases (e.g., SQL databases).
3) Examples- Spreadsheets. SQL databases.
Q8] What is the role of a database administrator? List any two responsibilities.
Ans) 1) The role of the data administrator is to coordinate all the activities of the database
system
2) The database administrator has a good understanding of the enterprise’s information
resources and needs.
3) Database administrator’s duties include:
a) Schema definition
b) Storage structure and access method definition
Q9] What is a transaction in a database system?
Ans) 1) A transaction is a collection of operations that performs a single logical function in a
database application
2) Transaction-management component ensures that the database remains in a consistent
state despite system failures (e.g., power failures and operating system crashes) and
transaction failures.
3) Concurrency-control manager controls the interaction among the concurrent
transactions, to ensure the consistency of the database.
Q10] What is unstructured data? Give two examples.
Ans) 1) Data that is not organized in a pre-defined manner is called unstructured data.
2) Includes text, images, videos, and social media posts.
3) Examples- Emails and Social media content.
Q11] What are the advantages of using structured data?
Ans) 1) Ease of Analysis: Simple to manipulate, aggregate, and analyze.
2) Supports complex queries and reporting.
3) Data Integrity: Enforces data integrity through constraints and relationships.
Example: Foreign key constraints to maintain referential integrity.
4) Scalability: Efficient storage and retrieval for large datasets.
Example: Indexing for faster search and retrieval.
Q12] Define an ER (Entity-Relationship) diagram. What is its primary use?
Ans) 1) Definition: An ER diagram visually represents entities, their attributes, and
relationships in a system.
2) Primary Use: It is used to model and design database structures.
4) Clarification: Helps clarify data requirements and interactions among stakeholders.
5) Guidance: Serves as a blueprint for database implementation.
Q13] What is relational algebra? Name any two operations in relational algebra with
examples.
Ans) 1) Relational algebra is a procedural query language used in relational databases to
manipulate and retrieve data.
2) It uses a set of operations to perform queries on relations(tables).
.3) Two Operations in Relational Algebra:
a) Selection( ): Retrieve rows that satisfy a given condition
Eg.: ( )(salary>5000). Retrieves all employees with a salary greater than 5000.
b) Projection( ):retrieve specific columns from a relation.
Eg: ( )(name,age). Retrieves only the name and the age column from the employee
table.
Q14] What is the difference between nominal and ordinal data?
Ans) 1) Ordinal Data: Data with a meaningful order but no fixed intervals between values.
Example: Customer satisfaction ratings (e.g., satisfied, neutral, dissatisfied).
2) Nominal Data: Data without an inherent order or ranking
Example: Types of fruits, categories of books.
What are different types of attributes in ER diagrams give example of each.
Ans) 1) Classes of Attributes
a) Single-valued attribute: A single-valued attribute can have only a single value.
Examples: A person can have only one social security number.
b) Multi-valued attributes: Multivalued attributes can have many values.
Examples: A person may have several college degrees.
Multivalued attributes are shown by a double line connecting to the entity.
c) Simple Attribute: A simple attribute cannot be subdivided.
Examples: Age, Sex, and Marital status
d) Composite attribute: A composite attribute can be further subdivided to
yield additional attributes.
Examples: ADDRESS, Street, City, State, Zip
PHONE NUMBER, Area code, Exchange number
e) Derived Attribute: A derived attribute is not physically stored within the database;
instead, it is derived by using an algorithm.
Example: AGE can be derived from the data of birth and
the current date.
Q17] Discuss the different types of relationships in ER diagrams.
Ans) In ER diagrams, relationships describe how entities are associated with one another.
Here are the main types of relationships:
1. One-to-One (1:1):
* Description: Each entity in the relationship corresponds to exactly one entity in the other
set.
* Example: Each person has one unique passport, and each passport is assigned to one
person.
2. One-to-Many (1:N):
* Description: One entity in the relationship can be associated with multiple entities in the
other set, but those entities can only relate back to one.
* Example: A teacher can teach multiple courses, but each course is taught by only one
teacher.
3. Many-to-One (N:1):
* Description: Multiple entities in one set can be associated with a single entity in another
set.
* Example: Many students can enrol in one course, but each course has many students
Q23] Explain the concept of levels of abstraction in a DBMS with examples
Ans) 1. Physical Level
* Definition: Details how data is physically stored.
* Example: Data stored in binary files or B-trees on a hard disk.
2. Logical Level
* Definition: Defines what data is stored and relationships among data.
* Example: Schema for a library system:
o Entities: Books (BookID, Title, AuthorID), Authors (AuthorID, Name)
o Relationship: An author can write multiple books.
3. View Level
* Definition: User-specific view of data, hiding complexities.
* Example:
o Student View: Displays enrolled courses and grades.
o Admin View: Allows adding courses and updating records.
