Database Fundamentals Quiz

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Questions and Answers

What is the primary reason for requiring a database in web applications?

To ensure that all user sessions are simultaneously stored in memory

To handle large volumes of data and ensure data persistence (correct)

To simplify coding by merging front-end and back-end data

To enhance aesthetic design of web pages

Which of the following correctly describes ACID semantics in relational databases?

Accuracy, Consistency, Isolation, Durability

Association, Concurrency, Integrity, Development

Accessibility, Capacity, Integration, Documentation

Atomicity, Consistency, Isolation, Durability (correct)

What characteristic makes NoSQL databases suitable for handling evolving applications?

Limited concurrent request handling capabilities

Strict adherence to predefined data schemas

Good organization of data storage that adapts over time (correct)

Ability to store hierarchical data efficiently

What is a defining feature of relational databases?

They store data in tables and define relationships between them Signup and view all the answers

What is a primary advantage of using a database for application data storage?

It allows for reliable storage and retrieval even under failure conditions Signup and view all the answers

What is the primary purpose of a foreign key in database tables?

To link to records in other tables Signup and view all the answers

How does SQL improve the efficiency of data queries?

It automates the data retrieval process based on user specifications Signup and view all the answers

Which command correctly inserts a new record into the Users table?

INSERT INTO Users (first_name, last_name, location) VALUES ('Ian', 'Malcolm', 'Austin, TX'); Signup and view all the answers

What advantage does creating an index provide when fetching data?

It allows for quicker lookup of records based on specified columns Signup and view all the answers

What is a common characteristic of relational databases?

They use primary keys to uniquely identify records within a table Signup and view all the answers

What happens during Step 3 of the transaction from Account A to Account B if an error occurs?

Steps 1, 2, and 3 are rolled back. Signup and view all the answers

What type of data are NoSQL databases specifically designed to handle?

Unstructured or semi-structured data Signup and view all the answers

Which ACID property ensures that transactions are permanent after being committed?

Durability Signup and view all the answers

What is a consequence of violating the isolation property in a transaction?

Concurrent transactions can affect each other. Signup and view all the answers

Which of the following properties must a system choose between during a network partition according to the CAP theorem?

Consistency and availability Signup and view all the answers

What does the BASE principle stand for in NoSQL databases?

Basically Available, Soft state, Eventually consistent Signup and view all the answers

What would occur if the account balance before a transaction is below the required threshold according to the consistency property?

The transaction will roll back. Signup and view all the answers

What is a common drawback of NoSQL databases concerning data consistency?

Data may become inconsistent or out of sync. Signup and view all the answers

Which of the following statements best describes the CAP theorem?

It reflects the trade-offs between consistency, availability, and partition tolerance. Signup and view all the answers

In the provided bank account transaction scenario, which property is violated if T2 acts on an intermediate state of the account balance?

Isolation Signup and view all the answers

In which scenario would a NoSQL database be preferred over a traditional SQL database?

When dealing with real-time web applications. Signup and view all the answers

Which of the following best describes eventual consistency in NoSQL databases?

Data will eventually converge to a consistent state, but may be inconsistent for a time. Signup and view all the answers

What is a primary benefit of having ACID properties in database transactions?

It simplifies reasoning about actions of the system. Signup and view all the answers

Which of the following is NOT a characteristic of atomicity in transactions?

The transaction can be partially completed. Signup and view all the answers

Which characteristic is a key advantage of NoSQL databases?

They are more scalable and failure tolerant than traditional databases. Signup and view all the answers

Which type of database does NOT natively support table joins?

NoSQL databases Signup and view all the answers

What command is used to insert a single document into a MongoDB collection?

db.collectionName.insertOne() Signup and view all the answers

Which command retrieves all documents from a collection in MongoDB?

db.collectionName.find() Signup and view all the answers

How can you specify a condition to find documents with a field value greater than a certain number in MongoDB?

db.collectionName.find({ field: $gt: number }) Signup and view all the answers

What does MongoDB automatically assign to each document for unique identification?

_id value Signup and view all the answers

What method is used to remove documents from a collection based on a matching condition?

db.collectionName.remove() Signup and view all the answers

Which of the following statements accurately describes the requirement for Object IDs in MongoDB?

Object IDs must be unique across documents. Signup and view all the answers

What command would you use to update specific fields of documents matching certain criteria in a MongoDB collection?

db.collectionName.update() Signup and view all the answers

For which of the following operations would you use the find() method with a JSON object as an argument?

To retrieve documents satisfying certain field conditions. Signup and view all the answers

What is a primary limitation of using joins in MongoDB?

Joins are not natively supported. Signup and view all the answers

Which condition determines whether the grades of a restaurant will be printed in the provided MongoDB query?

The restaurant must have more than one grade. Signup and view all the answers

What JavaScript method is used to iterate through each document in a collection in MongoDB?

forEach() Signup and view all the answers

In the example join operation, what is the expected outcome if a restaurant does not have a corresponding user document?

Nothing will be printed for that restaurant. Signup and view all the answers

Which field is used to find the corresponding student details in the provided solution to the class activity?

studentNo Signup and view all the answers

What will be printed if no match is found for a student's number in the MongoDB shell activity?

No match found for <student number> Signup and view all the answers

What is required before performing a join operation in MongoDB according to the provided content?

JavaScript code must be written. Signup and view all the answers

In the example, what structure does the user document utilize to identify users who reviewed restaurants?

The restaurant name. Signup and view all the answers

Study Notes

Web Databases (SQL and NoSQL)

Web databases are used to store and retrieve data for web applications.
SQL databases organize data in tables with rows and columns.
NoSQL databases offer flexible schemas and scalability.

Web Application Architecture

Web browsers (e.g., Chrome, Firefox, Safari) interact with web servers (e.g., Apache, Node) for data retrieval.
The storage system contains the database (e.g., MySQL, MongoDB) where data is stored.
Data transfers between components occur via the HTTP protocol over a Local Area Network (LAN) and the internet.

Why/When Do We Need a Database?

Data volume: Handling large amounts of data that cannot be stored in memory.
Data persistence: Ensuring data is accessible even during user logouts, power outages, or network issues.
Accurate data manipulation: Data manipulation like bank transactions requires precise, controlled manipulation.

Web App Storage Properties

Always available: Ensuring data access even with concurrent requests.
Scalable: Handling concurrent requests from various geographic locations.
Reliable/fault-tolerant: Data integrity even if parts of the system fail.
Well-organized to easily extract and organize application data.
Easily adapted to evolution of the application.
Easy to understand and maintain.

Relational Databases (SQL-based)

Data is stored in tables; Relations are used to link data between tables.
Tables improve data organization, easily representing relationships.
Queries easily process data from multiple tables.

Relational Database System (Details)

Tables are comprised of rows/tuples/records, which consist of columns/attributes/fields of a fixed type.
Data within a table is organized into predefined fixed categories that are stored in columns.
Columns have typed entries for specific categories of information (number, dates etc).
Data rows are identified using a unique key (primary key).

Database Schema

Schema defines the structure of the database.
Database structure consists of table names, table columns, and constraints.
Table columns are defined with specific types.

Example of a Table

Data is displayed in rows and columns and identified using a unique primary key.
The table structure has columns for identifying information along with typed data entries. (name, date, number, etc.)

SQL Example Commands

CREATE TABLE statement defines a table structure.
INSERT INTO statement adds a record/row.
DELETE FROM statement removes a record.
UPDATE statement modifies a record.
SELECT statements retrieve data.

Keys and Indexes

Primary keys uniquely identify each row in a table.
Secondary keys (indexes) are additional keys to speed up data retrieval.
Indexes can be used to more quickly identify specific rows of data by using a lookup function.

Table Joins

Joins combine information from multiple tables into one single table.
Tables can combine into a more convenient single view of the data in a database.

The Problem with Joins

Joins retrieve related documents/rows from multiple tables, which creates performance issues.
Joins are expensive in terms of calculation because of the many steps involved in finding the related rows.

SQL Databases have ACID Semantics

Atomicity: All operations succeed or fail entirely.
Consistency: Data validation rules are maintained.
Isolation: Concurrency control to prevent interference between transactions.
Durability: Committed data is reliably stored in the database.

Atomicity of Transactions

Transactions execute all steps completely or rollback in case of an error.
Error handling allows transaction operations to recover from an error.

Consistency

Data validation rules ensure that data in the database remains accurate after a transaction.
Rules include checks on the data integrity/accuracy of the data.

Isolation

Concurrent transactions do not interfere with each other.
Concurrent operations must be isolated/separated to prevent issues.

Durability

Committed transactions are permanently stored in the database.
Database operations (data writing in particular) remain in the database after a transaction.

ACID: Pros and Cons

Pros: Simpler reasoning about system actions, guaranteed correctness in failures.
Cons: Performance costs related to guarantees, cannot guarantee availability when network fails. The CAP Theorem applies here.

The activity entails evaluating several use cases. Database selection is crucial in these situations.

Solution to the Activity [Database selection justification]

The solution would justify the appropriate database choice (SQL or NoSQL) for each scenario of the activity presented.

What are NoSQL Databases?

They manage unstructured or semi-structured data.
They have adjustable database structures/schemas. Very flexible.
They offer high scalability.
Designed for large-scale data processing in real-time applications like web applications.

NoSQL Databases (Specific Details)

They do not natively support table joins and require manual programming implementation.
They often do not strictly follow database ACID properties but instead provide eventual consistency.

CAP Theorem [Brewer'99]

Trade-offs exist for a variety of scenarios involving databases for web applications.
Consistency, availability, and partition tolerance are three properties related to database systems and their interactions with network environments.
Selecting a particular strategy often implies a specific trade-off related to a situation or operational scenario.

BASE principle [NoSQL database methodology]

Basically available, soft state, and eventually consistent.
It's a principle that is often associated with NoSQL database systems
It emphasizes availability and flexibility rather than strict consistency like databases based on SQL methodologies. Eventual consistency is a key element to understand.

Eventual Consistency

NoSQL databases eventually become consistent. It's the point in time at which the database contents are fully consistent.
It is often not immediate and can take a while for the data to be perfectly balanced and consistent .

SQL Vs. NoSQL - Comparison

Types: SQL has one main type; NoSQL has multiple types (e.g., key-value, document, graph).
Examples: SQL examples include MySQL, SQLite, and Oracle Database; NoSQL includes MongoDB, Cassandra, and others.
Data Storage Model: SQL stores data in rows and columns; NoSQL stores data in documents.
Schemas: SQL schemas are fixed, NoSQL schemas are adjustable.

SQL Vs. NoSQL - Scaling

SQL databases typically scale vertically (increasing single server power); NoSQL typically scales horizontally (distributing data over multiple machines).
Scaling choices influence whether the system can handle load and availability.

SQL Vs. NoSQL - Transactions

SQL supports transactions; NoSQL may offer certain levels of transaction functionality, but is frequently not fully supportive of transactions.

SQL Vs. NoSQL - Consistency

SQL databases require strong consistency, while NoSQL databases may provide tunable or eventual consistency (trade-off with scalability and availability).

Class Activity: [Appropriate database selection based on scenario]

Students evaluate several situations to determine the appropriate database.

MongoDB (Document-Oriented NoSQL)

Documents are the key elements of data organization, analogous to tables in SQL.
Data is stored in JSON format in MongoDB.
Databases are composed of collections.
Documents have a 'unique identifier' field to uniquely identify them in a collection.

MongoDB: Data Types

Valid JSON data types are present for a MongoDB database.

MongoDB: Example Dataset

JSON/BSON format example dataset for a MongoDB structure.

Databases and Collections (MongoDB structure)

A database is composed of multiple collections, analogous to SQL tables.
Collections hold many records in MongoDB format. Each record is a document.

Insert into a Database (MongoDB)

db.collectionName.insert(document in JSON) method is used for inserting new documents. Inserting data usually occurs through programming code.

Finding Objects (MongoDB Queries)

db.collectionName.find() (returns all documents)
db.collectionName.find(JSON_object) (returns only documents satisfying criteria)

Examples of Queries (MongoDB)

Query examples (finding data using specific criteria).

Object_id (MongoDB key)

_id is a unique identifier for each document in a MongoDB collection.
It's automatically generated, ensuring uniqueness and database integrity.

Update (MongoDB Updates)

db.collectionName.update(query, updateObject) updates existing entries.

Remove (MongoDB Removal)

db.collectionName.remove(query) removes existing entries from a MongoDB collection based on criteria in the query.

Operations on Each Record (MongoDB functions)

Examples of using .forEach() in MongoDB to operate on specific elements or criteria.

Table Joins in MongoDB

Table joins are not supported by MongoDB directly. Manual programming/implementation is required to handle these kinds of joins.

Example: Join Operation (MongoDB implementation)

Example that shows how to do a join in MongoDB by extracting the necessary fields and documents to represent a join.

Class Activity: [Join operation for two different collections]

Solution to the Activity (MongoDB/Javascript join operation)

Example of joining two MongoDB collections together using code.

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Description

Test your knowledge on key database concepts essential for web applications. This quiz covers topics like ACID semantics, relational databases, and NoSQL advantages. Perfect for anyone looking to solidify their understanding of database management.