HW 3 – Document data stores. MongoDB

(5 points)

1. Design the data structures based on the analytical tasks (see HW1) that are intended to be solved with MongoDB.
   • The structures must be designed so that the target queries are feasible.
   • Avoid overly nested documents.
     • Denormalize only when it benefits performance; do not create overly deep nesting that complicates queries.
2. Insert the data into MongoDB using the CSV/JSON generated for the project (see HW0). Use the Base dataset as defined in HW0.
   • Load only what is needed for tasks/comparisons. Do not import unnecessary data.
3. Implement and run the queries (see HW1). Create supporting indexes for every analytical query.
   • Use the Aggregation Pipeline; do not use `$where`, server-side JavaScript, or `mapReduce`.
   • Apply appropriate time filters, groupings, and KPIs as required by your HW1 tasks (do not hardcode specific fields like “country/action” if your domain differs).
   • For each query, include `db.collection.explain(“executionStats”).aggregate(…)` (or the relevant command) and show a compact excerpt of the plan in the report.
4. Prepare a report and include:
   • the text from HW0 and HW1 (edited if necessary);
   • the collections creation and document-insertion commands, with explanations of why this structure was chosen;
   • the data import code;
   • the queries used to solve the analytical tasks. For each task, provide:
     • the task number (as in the previous work);
     • the verbal description of the task;
     • the query code with explanations;
     • a screenshot (or excerpt) of the query result and the `explain(“executionStats”)` output.

Note. If some analytical tasks turn out to be infeasible or meaningless, you may replace them with others and propagate the corresponding changes to the earlier work (HW0/HW1).

Submit to the BRUTE system:

• HW3.docx file.

Submit to the NoSQL server (nosql.felk.cvut.cz) the hw3.js file with MongoDB commands with short comments.

• Submission:
  • hw3.js: JavaScript script with MongoDB database commands
• Execution:
  • Execute the following shell command to evaluate the whole MongoDB script

mongosh --port 42222 -u login -p password database hw3.js

• $login is your username, e.g. f25_login
• $database - database to connect to (same as login)
• $password is your password (Use the same password you received for your account at the beginning of the semester)
• $file is a file with MongoDB queries to be executed, i.e. hw3.js
• Double dashes before port
• Tools:
  • MongoDB 7.0.14 (installed on the NoSQL server)
• References:
  • https://docs.mongodb.com
• Server: nosql.felk.cvut.cz
  • Do not forget to execute the homework submission script!
• Deadline: Sunday 23. 11. 2025 until 23:59