How to implement a simple DBMS?

Question

Database

Hello, the university issued a project work to write a system for recording scientific papers. The data will need to be collected from sites such as Google Schoral, DBLP, etc.
The task includes developing an ER database model, writing data to any database I want and implementing a web interface.
The most difficult task is to develop your own DBMS and transfer data to it, it must be able to: SELECT, UPDATE, DELETE, INSERT, JOIN, SORT BY, GROUP BY. There is also a restriction on the use of only 1 file for storing the database in physical form. I was looking for what data structures modern databases use. Found B+ tree. I plan to load everything into RAM when initializing the DB application.
There are many questions about this:
1) Is my choice successful?
2) How can I write all this into 1 file.
3) Question on keys. Each article, author, etc. will have a numeric key with an increment of 1. But there will also be a search by the author's name, article title, tags, etc. How to do it? Table hash? In this matter, I still don’t even know what to do.
The task itself

Answer 1

fallabs.com/tokyocabinet

Answer 2

simple