Ruby on Rails

Table names are all lowercase by convention (and plural). Model names are singular, capitalized CamelCase. In fact, it is a ruby-wide convention that class names are capitalized CamelCase (not just rails).
 

As for having a prefix, you might be interested in the #table_name_prefix property:

http://api.rubyonrails.org/classes/ActiveRecord/Base.html#method-c-table_name_prefix

This would allow you to have tables named:

tc_projects
tc_employees
tc_periods
tc_datum

And model classes respectively:

class Project < ActiveRecord::Base
  table_name_prefix = "tc_"
end
...
class Datum < ActiveRecord::Base
  table_name_prefix = "tc_"
end

In order to then DRY up your code a bit, you *might* be able to use an abstract base class:

class TcPrefix < ActiveRecord::Base
  table_name_prefix = "tc_"
  abstract_class = true
end

class Project < TcPrefix
end
...
class Datum < TcPrefix
end

I haven't tested this to see if this variation works correctly. I'd give a try though.