====== HW 3 – Document data stores. MongoDB ======
**(5 points)**

  - 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.
  - 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.
  - 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.
  - 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
        <code bash>mongosh --port 42222 -u login -p password database hw3.js</code>
      * ''$login'' is your username, e.g. ''f25_login''
      * ''$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:
    * [[http://www.mongodb.com/|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