General idea is similar to Hexagonal or Ports and Adapters architecture. Web and DB concerns depend on the application core, not the other way around.
/web -- depends on --> /db /web -- depends on --> /lib /db -- depends on --> /lib /lib -- depends on --> nothing from from /web or /db
Gemfile
Gemfile.lock
README.md
Rakefile
config.ru
app.rb
db.rb
/config
db.rb
environment.rb
puma.rb
/db
/mappers
some_mapper.rb
/migrate
migration_001.rb
sequel_mapper.rb
/lib
<project_name>.rb
/<project_name>
... files
/helpers
some_helper.rb
/public
/css
styles.css
/img
favicon.png
hoboken.png
sinatra.png
/js
app.js
/views
index.erb
layout.erb
/test
test_helper.rb
/<project_name>
/db
some_mapper_test.rb
/support
rack_test_assertions.rb
app_test.rb