某個(gè)數(shù)據(jù)庫(kù)的DDL的表關(guān)系搞不清楚

某個(gè)數(shù)據(jù)庫(kù)的DDL如下所示，請(qǐng)問帖子應(yīng)該是哪個(gè)表？請(qǐng)解釋一下三個(gè)表的作用。
create table t_forum
(
forum_id int(11) not null ,
forum_name varchar(150) not null default 'forum',
forum_desc varchar(255) default NULL,
primary key (forum_id)
);

create table t_post
(
post_id int(11) not null ,
topic_id int(11) not null default 0,
user_id int(11) not null default 0,
post_text text,
post_attach blob,
post_time datetime default NULL,
primary key (post_id)
);

create table t_topic
(
topic_id int(11) not null ,
forum_id int(11) not null default 0,
topic_title varchar(100) not null default '',
user_id int(11) not null default 0,
topic_time datetime default NULL,
topic_views int(11) default 1,
topic_replies int(11) default 0,
primary key (topic_id)
);