text: CREATE TABLE projects(
      id serial PRIMARY KEY,
      name varchar(256) NOT NULL,
      created_by varchar(256) NOT NULL,
      UNIQUE (name)
  );
  
  CREATE TABLE layers(
      id serial PRIMARY KEY,
      project_id int NOT NULL REFERENCES projects,
      in_project_index int NOT NULL,
      name varchar(256) NOT NULL,
      type varchar(256) NOT NULL,
      UNIQUE (project_id, name)
  );
  
  CREATE TABLE relation_layer_span_roles(
      id serial PRIMARY KEY,
      layer_id int NOT NULL REFERENCES layers,
      in_layer_index int NOT NULL,
      name varchar(256) NOT NULL,
      target_layer_name varchar(256) NOT NULL,
      UNIQUE (layer_id, name)
  );
  
  CREATE TABLE attributes(
      id serial PRIMARY KEY,
      layer_id int NOT NULL REFERENCES layers,
      in_layer_index int NOT NULL,
      name varchar(256) NOT NULL,
      type varchar(256) NOT NULL,
      UNIQUE (layer_id, name)
  );
  
  CREATE TABLE enum_attribute_values(
      id serial PRIMARY KEY,
      attribute_id int NOT NULL REFERENCES attributes,
      in_attribute_index int NOT NULL,
      name varchar(256) NOT NULL,
      UNIQUE (attribute_id, name)
  );
  