Server Backend concepts

CRUD Operations:
CRUD is an acronym that comes from the world of computer programming and refers to the four functions that are considered necessary to implement a persistent storage application: create, read, update and delete.
Create:
The create function allows users to create a new record in the database. In the SQL relational database application, the Create function is called INSERT. In Oracle HCM Cloud, it is called create. Remember that a record is a row and that columns are termed
attributes. A user can create a new row and populate it with data that corresponds to each attribute, but only an administrator might be able to add new attributes to the table itself.
Read:
The read function is similar to a search function. It allows users to search and retrieve specific records in the table and read their values. Users may be able to find desired records using keywords, or by filtering the data based on customized criteria. For example, a database of cars might enable users to type in "1996 Toyota Corolla", or it might provide options to filter search results by make, model and year.
Update:
The update function is used to modify existing records that exist in the database. To fully change a record, users may have to modify information in multiple fields. For example, a restaurant that stores recipes for menu items in a database might have a table whose attributes are "dish", "cooking time", "cost" and "price". One day, the chef decides to replace an ingredient in the dish with something different. As a result, the existing record in the database must be changed and all of the attribute values changed to reflect the characteristics of the new dish. In both SQL and Oracle HCM cloud, the update function is simply called "Update".
Delete:
The delete function allows users to remove records from a database that is no longer needed. Both SQL and Oracle HCM Cloud have a delete function that allows users to delete one or more records from the database. Some relational database applications may permit users to perform either a hard delete or a soft delete. A hard delete permanently removes records from the database, while a soft delete might simply update the status of a row to indicate that it has been deleted while leaving the data present and intact.

JWT:
JSON Web Token, is an open standard used to share security information between client and server. JWTs differ from other web tokens in that they contain a set of claims. Claims are used to transmit information between two parties. What these claims are depends on the use case at hand. A JWT is a string made up of three parts, separated by dots (.), and serialized using base64. In the most common serialization format, compact serialization.

Mongoose:
Mongoose is a Node. js-based Object Data Modeling (ODM) library for MongoDB. It is akin to an Object Relational Mapper (ORM) such as SQLAlchemy for traditional SQL databases. The problem that Mongoose aims to solve is allowing developers
to enforce a specific schema at the application layer.

Relational database (MySql):
Relational database is a program used to maintain a relational database.RDBMS is the basis for all modern database systems such as MySQL, Microsoft SQL Server, Oracle, and Microsoft Access.

Express:
Express is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications. The primary use of Express is to provide server-side logic for web and mobile applications, and as such it's used all over the place.
Companies which use Express as a foundation of their internet presence include: