 	name varchar(255) not null,
 	description varchar(255) DEFAULT NULL,
 	url varchar(255) DEFAULT NULL,
-	study varchar(255) DEFAULT NULL,
+	external_reference varchar(255) DEFAULT NULL,
+	study_type set('GWAS'),
 	
 	primary key( study_id ),
-	unique key name_idx(name),
 	key source_idx (source_id)
 );
 

	variation_annotation_id int(10) unsigned not null auto_increment,
	variation_id int(10) unsigned not null,
	phenotype_id int(10) unsigned not null,
	source_id int(10) unsigned not null,
	study varchar(30) default NULL,
	study_type set('GWAS'),
	local_study_id int(10) default NULL,
	associated_gene varchar(255) default NULL,
	associated_variant_risk_allele varchar(255) default NULL,

@column variation_annotation_id					Primary key, internal identifier.
@column variation_id										Foreign key references to the @link variation table.
@column phenotype_id										Foreign key references to the @link phenotype table.
@column study_id												Foreign key references to the @link study table.
@column local_study_id									Foreign key references to the @link study table.
@column associated_gene									Common gene(s) name(s) associated to the variation.
@column associated_variant_risk_allele	Allele associated to the phenotype.
