Oracle：密钥约束

我在Oracle的SQL中有一个实体：

我想知道“ UF”代表什么？我已经编写了SQL代码，但不知道如何将“ UF”属性表示为约束。

CREATE TABLE entry (
    entryno           NUMBER(4) NOT NULL,
    carndate          DATE NOT NULL,
    entrystarttime    DATE NOT NULL,
    entryfinishtime   DATE NOT NULL,
    entryplace        NUMBER(4) NOT NULL,
    charname          VARCHAR2(30) NOT NULL,
    compno            NUMBER(4) NOT NULL,
    eventypecode      CHAR(3) NOT NULL,
    teamname          VARCHAR2(30) NOT NULL
);

ALTER TABLE entry ADD CONSTRAINT entry_pk PRIMARY KEY ( entryno,     
                                                        carndate );

ALTER TABLE entry
    ADD CONSTRAINT entry_charity_fk FOREIGN KEY ( charname )
        REFERENCES charity ( charname );

ALTER TABLE entry
    ADD CONSTRAINT entry_carnival_fk FOREIGN KEY ( carndate )
        REFERENCES carnival ( carndate );

ALTER TABLE entry                       #
    ADD CONSTRAINT entry_competitor_fk FOREIGN KEY ( compno )
        REFERENCES competitor ( compno );

ALTER TABLE entry                       #
    ADD CONSTRAINT entry_event_fk FOREIGN KEY ( carndate, eventypecode )
        REFERENCES evenet ( carndate, eventypecode );

ALTER TABLE entry
    ADD CONSTRAINT entry_team_fk FOREIGN KEY ( teamname, carndate )
        REFERENCES team ( teamname,carndate );

ALTER TABLE entry
    ADD CONSTRAINT ... ("UF")