Version control systems, Git and GitHub and databases

Question 1

What is version control system

Answer 1

It’s a system that allows to manage changes made to a software project over time
* Tracking changes
- revision history
- list of (snapshots +
timestamps)
- diff between snapshots
* Reverting to previous versions (snapshots) of the code
* Easing collaboration
- keeps track and helps
unify conflicting versions
of the same file

Question 2

What are the two types of vcs

Answer 2

1.Centralized VCS
2.Distributes VCS

Question 3

Explain what a centralized VCS is

Answer 3

➢ central server with single main repository
➢ revision history on the central server only
➢ need to be connected to the server for
most operations
➢ multiple co-existing versions of the same
artefacts if modified by different persons
➢ e.g., SVN

Question 4

Explain what a distributed VCS is

Answer 4

➢ central server + local copy of the
repository with revision history
➢ every dev has full control of their local
repository
➢ most operations do not need connection
to the server
➢ merge modifications with the new
modifications of the central repository
➢ e.g., Gi

Question 5

What is Git

Answer 5

It’s a distributed VCS with the key features like tracking changes and collaboration

Question 6

Explain Working Directory vs Staging Area vs Local Git Repository vs Remote Git Repository

Answer 6

Working directory is where you have all the files open on your personal laptop and staging area is where you code goes when you call git add, local repository is where your code goes after git commit and finally your code goes to remote git repository when you call git push

Question 7

How do you clone an existing repository

Answer 7

git clone <url></url>

Question 8

How to turn a local directory into a git repository

Answer 8

git init

Question 9

How to stage untracked files

Answer 9

git add file.text

Question 10

How to check what files are untracked in the working tree

Answer 10

git status

Question 11

How to create a new snapshot

Answer 11

git commit –m “message”

Question 12

How to list the commits in reverse chronological order

Answer 12

git log

Question 13

How to get the abbreviated stats for each commit

Answer 13

git log –stat

Question 14

How to unstage files from staged to modified

Answer 14

git reset HEAD file.txt

Question 15

How to discard changes in the working tree to revert the file before modification
or replace it with the one of last snapshot

Answer 15

git checkout file.txt or edit manually

Question 16

How to update the changed files/git message of the last commit

Answer 16

git commit –amend
> git commit –m “added files lectures 1 to 5”
> git add lecture-6.pdf
> git commit –amend –m “added files lectures 1 to 6

Question 17

How to undo changes of a commit and does not delete the commit
and replays it in reverse
and create a new commit for reverting the change

Answer 17

git revert <commit></commit>

Question 18

What are remote repositories

Answer 18

They are versions of your project hosted somewhere else

Question 19

what command do you use to show the remotes of your repository

Answer 19

git remote –v

Question 20

What command do you use to download data from the remote repo to your local repo

Answer 20

git fetch

Question 21

what does git pull do?

Answer 21

it fetches + merges data with your working tree
- pull = fetch + merge

Question 22

what command do you use to send your commits to the remote repository

Answer 22

git push

Question 23

What does merge do

Answer 23

If files are modified after your last commit > git pull
➢ If there is at least a commit you don’t have on your local repo
➢ your push is rejected
➢ to continue, you have to merge

You must first pull the commits you don’t have to your local repository
* If no conflict, the merge is automatic
* If conflicts exist, you must solve them manually

Question 24

What is data persistence?

Answer 24

Data created in the context of a running process must persist/be recovered after the process has ended therefore must be stored in a long-lasting storage medium.

Question 25

What are data persistence approaches

Answer 25

o data files o databases

Question 26

What are data files

Answer 26

they are file systems stored on disk, storing regular files such as documents and images.They are flat-file databases(e.g.,CSV and JSON data)

Question 27

what are the pros of data files

Answer 27

They are easy to understand and easy to work with.

Question 28

What are the cons of using data files

Answer 28

- suboptimal storage usage - suboptimal retrieval performance

Question 29

Define databases

Answer 29

They are organized collection of structured information designed to store and retrieve data efficiently.

Question 30

What are the cons of using databases

Answer 30

Optimal storage usage and optimal retrieval performance

Question 31

What are the cons of using databases

Answer 31

- they are complex to work with - They require specialized maintenance and operators

Question 32

What is database management system(DBMS)

Answer 32

-It's a software system that enables users to define, create, maintain and control access to the database -It's where databases are managed.

Question 33

Define relational databases

Answer 33

- They store data in tables which can be linked to one another. -It's maintained with relational database management system(RDBMS) E.g.: MySQL, PostgreSQL (open source), Oracle Database, Microsoft SQL Server, DB2 (IBM) - They use Structured Query Language(SQL) for querying data in relational databases.

Question 34

Discuss NoSQL Databases

Answer 34

Non-SQL or Not-only SQL o do not use traditional SQL queries o large amounts of unstructured or semi- structured data ▪ usually, simple data o flexible and scalable Unstructured data: text, image / Semi-structured data: JSON, XML, CSV Key-value database: collection of key-value pairs (e.g., Riak and Redis) Graph database: Store and query graph data (nodes and edge) (e.g., Neo4j, Neptune, OrientDB)

Question 35

Discuss tables in relational database

Answer 35

○ name ○ columns + rows ○ fixed number of columns (can be modified) ○ theoretically unlimited number of rows

Question 36

Discuss columns in relational database

Answer 36

○ name + data type ▪ e.g., McGillId (int), year (date), firstName (char), description (text) ○ represent attributes of the data

Question 37

Discuss rows in relational database

Answer 37

○ record / observation / entry ○ instance of the table columns ○ has a value for each column

Question 38

Relational database design

Answer 38

1) Dividing tables to avoid redundancies * McGillId, FirstName, LastName in the same table * Course, Name in the same table 2) Identifying each instance with a unique identifier * one primary key per table * preferably, one column * can be a combination of columns * e.g., McGillId, CourseID (underlined in the table) 3) Referring to rows in other tables o as much foreign keys as necessary o foreign key = column whose values are primary keys of another table (refers to one row) => Still redundant information in Offering