¹ØϵÊý¾ÝÄ£ÐÍÉϵIJÙ×÷

ÔÚÉÏÒ»½Ú£¨Relational Data Model Formalities£©ÀÎÒÃǶ¨ÒåÁ˹ØϵģÐ͵ÄÊýѧ¸ÅÄî¡£ÏÖÔÚÎÒÃÇÖªµÀÁËÓùØϵÊý¾ÝÄ£ÐÍÈçºÎ´æ´¢Êý¾Ý£¬µ«ÊÇÎÒÃÇ»¹²»ÖªµÀÈçºÎ´ÓÕâЩ±íÀïÃæ¼ìË÷ijЩ¶«Î÷¡£ÀýÈ磬ijÈËÏëÖªµÀÏúÊÛ²¿¼þ 'Screw' µÄËùÓеĹ©Ó¦É̵ÄÃû³Æ¡£Òò´Ë¶¨ÒåÁËÁ½ÖÖ²î±ðÏ൱´óµÄÓÃÓÚ±íʾ¶Ô¹ØϵµÄ²Ù×÷µÄ·ûºÅ£º

¹Øϵ´úÊý

¹Øϵ´úÊýÊÇ E. F. Codd ÓÚ 1972 Ê×ÏÈÌá³öµÄ¡£Ëü°üÀ¨Ò»¸ö¶Ô±í½øÐвÙ×÷µÄ¼¯ºÏ£º ¹ØÓÚ¹Øϵ´úÊýµÄ¸üÏêϸµÄÃèÊöºÍ¶¨Ò壬Çë²Î¿¼[Ullman, 1988] »ò [Date, 1994]¡£
 
Àý 69-3. ʹÓùØϵ´úÊýµÄÒ»¸öÀý×Ó

»ØÒäÒ»ÏÂÎÒÃDzûÃ÷µÄËùÓпÉÒÔÓÃÓï´ÓÊý¾Ý¿âÀï¼ìË÷Êý¾ÝµÄ¹Øϵ²Ù×÷·û¡£ÏÖÔÚÎÒÃÇ¿ÉÒԻص½Ç°Ò»ÕµÄÀý×ÓÀ¹ØϵÊý¾ÝÄ£ÐÍÀïµÄ²Ù×÷£©£¬ÄÇʱÎÒÃÇÐèÒªÖªµÀÏúÊÛ²¿¼þ Screw µÄËùÓй©Ó¦É̵ÄÃû³Æ¡£ÏÖÔÚÎÒÃÇ¿ÉÒÔÓÃÏÂÃæµÄ¹Øϵ´úÊýµÄ²Ù×÷»Ø´ðÕâ¸öÎÊÌâÁË£º

¦ÐSUPPLIER.SNAME(¦ÒPART.PNAME='Screw'(SUPPLIER ¡Á SELLS ¡Á PART))
ÎÒÃdzÆÕâÑùµÄ²Ù×÷ÊÇÒ»´Î²éѯ¡£Èç¹ûÎÒÃǶÔÎÒÃǵÄÀý×Ó±í£¨The Suppliers and Parts Database£©½øÐÐÉÏÊö²éѯ¼ÆË㣬ÎÒÃǽ«»ñµÃÏÂÃæ½á¹û£º
                             SNAME
                            -------
                             Smith
                             Adams

¹Øϵ΢»ý·Ö

¹Øϵ΢»ý·Ö»ùÓÚµÚһ˳ÐòÂß¼­£¨first order logic£©¡£¹Øϵ΢»ý·ÖÓÐÁ½¸ö±äÖÖ£º ÎÒÃÇÖ»´òËãÌÖÂۼǼ¹Øϵ΢»ý·Ö£¬ÒòΪËüÊÇ´ó¶àÊý¹ØϵÓïÑÔ±³ºóµÄÊýѧ»ù´¡¡£ÓйØDRC £¨µ±È»»¹ÓРTRC£©µÄÏêϸÌÖÂÛ£¬²ÎÔÄ Date, 1994 »ò Ullman, 1988¡£

¼Ç¼¹Øϵ΢»ý·Ö

ÔÚ TRC ÀïʹÓõIJéѯÊÇÕâÑùµÄÐÎʽ£ºx(A) &mid F(x)£¬ÕâÀï x ÊÇÒ»¸ö¼Ç¼±äÁ¿£¬ A ÊÇÊôÐԵļ¯ºÏ¶ø F ÊÇÒ»¸ö¹«Ê½¡£Éú³ÉµÄ¹Øϵ°üº¬ËùÓÐÂú×ã F(t) µÄ¼Ç¼ t(A)¡£

Èç¹ûÎÒÃÇÏëÓàTRC »Ø´ðÀý×Ó Ò»¸öʹÓùØϵ´úÊýµÄ²éѯ ÀïµÄÎÊÌ⣬ÎÒÃÇ¿ÉÒÔд³öÏÂÃæ²éѯ£º

     {x(SNAME) &mid x ¡Ê  SUPPLIER ¡Ä  \nonumber
                       &exist y ¡Ê  SELLS &exist z  ¡Ê  PART (y(SNO)=x(SNO) ¡Ä  \nonumber
                        z(PNO)=y(PNO)  ¡Ä  \nonumber
                        z(PNAME)='Screw')} \nonumber
¶Ô ¹©Ó¦É̺Ͳ¿¼þÊý¾Ý¿â ¼ÆËãÕâ¸ö²éѯͬÑùµÃ³öÓë Ò»¸öʹÓùØϵ´úÊýµÄ²éѯÏàͬµÄ½á¹û¡£

¹Øϵ´úÊýÓë¹Øϵ΢»ý·ÖµÄ±È½Ï

¹Øϵ´úÊýºÍ¹Øϵ΢»ý·ÖÓÐ×ÅÏàͬµÄ±í´ïÄÜÁ¦£»Ò²¾ÍÊÇ˵£¬ËùÓпÉÒÔÓùØϵ´úÊý±í´ïµÄ²éѯ¶¼¿ÉÒÔʹÓùØϵ΢»ý·ÖÀ´±í´ï£¬·´Ö®ÒàÈ»¡£Õâ¸ö½áÂÛÊ×ÏÈÊÇ E. F. Codd ÔÚ 1972 ÄêÖ¤Ã÷µÄ¡£Õâ¸öÖ¤Ã÷ÊÇ»ùÓÚÒ»¸öËã·¨£¨¡°Codd µÄ¹éÄÉËã·¨¡±£©£¬ÀûÓÃÕâ¸öËã·¨£¬Ò»¸öÈÎÒâµÄ¹Øϵ΢»ý·ÖµÄ±í´ïʽ¿ÉÒÔ¹éÄÉΪһ¸öÓïÒåÉÏÏàµÈµÄ¹Øϵ´úÊýµÄ±í´ïʽ¡£¹ØÓÚÕâЩ¸üÏêϸµÄÌÖÂÛ£¬Çë²Î¿¼ Date, 1994 ºÍ Ullman, 1988¡£

ÓÐʱºòÎÒÃÇ˵»ùÓÚ¹Øϵ΢»ý·ÖµÄÓïÑԱȻùÓÚ¹Øϵ´úÊýµÄÓïÑÔÊǸü "¸ß¼¶µÄ" »òÕß "¸üÃèÊöÐÔµÄ" ÓïÑÔ£¬ÒòΪ´úÊý£¨²¿·ÖÉÏ£©ËµÃ÷Á˲Ù×÷µÄ¹ý³Ì¶ø΢»ý·Ö°ÑÕâЩ¹ý³ÌÁô¸ø±àÒëÆ÷»òÕß½âÊÍÆ÷ÒÔ¾ö¶¨¼ÆËãµÄ×îÓÐЧ˳Ðò¡£

¸