types
 CourseId = seq of char;
 TopicId = seq of char;
 InstId = seq of char;
 UserId = seq of char;
 UrlId = seq of char;

 FMESOE :: courses:     Courses
           urls:        UrlDb
           alltopics:   TopicDb
           countries :  CountrieDb
           users : UsersDb               
inv fmesoe == coursesOk(fmesoe);

 Courses = map CourseId to Course;      -- map CourseId to Course

 UrlDb = map UrlId to Url ;

 TopicDb = map TopicId to Topic;        -- map TopicId to Topic

 CountrieDb = map InstId to UrlId; -- map Instituicao to Pais

 Course :: ref : seq of char
                 year: seq of char
                 url : UrlId
                 inst : InstId          -- instituicao
                 contact: set of UrlId  -- set of UserId
                 topics: set of TopicId -- set of TopicId
                 langs: set of UrlId
                 tools: set of UrlId;

 Topic :: desc: seq of char             -- descricao    
                keywords: set of UrlId;         -- set of filhos

 Url :: name: seq of char       
              http: seq of char
              alt: seq of char
              email: seq of char
              type : set of seq of char;

 UsersDb = map UserId to User;  -- map UserId(Email) to User

 User :: name : seq of char
               pass : seq of char