+--------------------+         +---------------------+
  |   providers        |         | project_providers   |
  |--------------------|         |---------------------|
  | user_id            |         | project_id          |
  |                    |<--------+ provider_id         |<------+
  |                    |         |                     |       |
  +--------------------+         +---------------------+       |
          ^                                                    |
          |                                                    |
          |                                                    |
 +--------+------------+              +------------------------+-------+
 | offered_categories  |              | project_provider_categories    |
 |---------------------|              |--------------------------------|
 | provider_id         |              | project_provider_id            |
 | provider_category_id|              | provider_category_id           |
 |                     |              |                                |
 +----------+----------+              +---+----------------------------+
            |                             |
            |                             |
            |                             |
            |                             v
            |       +-----------------------------+
            +------>|  provider_categories        |
                    |-----------------------------|<--------------+
                    |                             |               |
                    +-----------------------------+               |
                                                                  |
                                                                  |
                                                       +----------+-------------------------+
                                                       |  required_categories               |
  +--------------------------------+                   |------------------------------------|
  |project_required_categories     |                   | project_required_category_id       |
  |--------------------------------| <-----------------+ user_id (el que da de alta el rqm) |
  |project_id                      |                   | provider_category_id               |
  |                                |                   |                                    |
  +--------------------------------+                   +------------------------------------+