{"id":6372,"date":"2024-07-18T20:28:47","date_gmt":"2024-07-18T12:28:47","guid":{"rendered":"https:\/\/t.n-years.com\/?p=6372"},"modified":"2024-07-18T20:28:47","modified_gmt":"2024-07-18T12:28:47","slug":"%e6%95%b0%e6%8d%ae%e5%ba%93-bcnf","status":"publish","type":"post","link":"https:\/\/t.n-years.com\/?p=6372","title":{"rendered":"\u6570\u636e\u5e93 BCNF"},"content":{"rendered":"<p>BCNF\uff0c\u5168\u79f0\u4e3a <strong>Boyce-Codd Normal Form<\/strong>\uff08\u535a\u4f0a\u65af-\u79d1\u5fb7\u8303\u5f0f\uff09\uff0c\u662f\u5173\u7cfb\u6570\u636e\u5e93\u4e2d\u7684\u4e00\u79cd\u89c4\u8303\u5316\u5f62\u5f0f\u3002BCNF \u662f 3NF\uff08\u7b2c\u4e09\u8303\u5f0f\uff09\u7684\u5f3a\u5316\u7248\u672c\uff0c\u7528\u4e8e\u6d88\u9664\u6570\u636e\u5e93\u8868\u4e2d\u7684\u5197\u4f59\u6570\u636e\uff0c\u5e76\u786e\u4fdd\u6570\u636e\u7684\u4e00\u81f4\u6027\u548c\u5b8c\u6574\u6027\u3002\u5b83\u7531 Codd \u7684\u540c\u4e8b Raymond Boyce \u548c Codd \u672c\u4eba\u63d0\u51fa\u3002<\/p>\n<h3>BCNF \u7684\u5b9a\u4e49<\/h3>\n<p>\u4e00\u4e2a\u5173\u7cfb R \u6ee1\u8db3 BCNF\uff0c\u5982\u679c\u5bf9\u4e8e\u5173\u7cfb\u4e2d\u7684\u6bcf\u4e00\u4e2a\u975e\u5e73\u51e1\u7684\u51fd\u6570\u4f9d\u8d56 X -&gt; Y\uff0cX \u90fd\u662f\u4e00\u4e2a\u8d85\u952e\uff08superkey\uff09\u3002<\/p>\n<ul>\n<li><strong>\u51fd\u6570\u4f9d\u8d56\uff08Functional Dependency\uff09<\/strong>\uff1a\u5bf9\u4e8e\u5173\u7cfb R \u4e2d\u7684\u4efb\u610f\u5c5e\u6027\u96c6 X \u548c Y\uff0c\u5982\u679c\u5bf9\u6bcf\u4e00\u4e2a\u5408\u6cd5\u7684\u5143\u7ec4 t1 \u548c t2\uff0c\u6709 t1[X] = t2[X] \u5c31\u8574\u542b t1[Y] = t2[Y]\uff0c\u90a3\u4e48\u79f0 X -&gt; Y \u662f\u5173\u7cfb R \u4e0a\u7684\u4e00\u4e2a\u51fd\u6570\u4f9d\u8d56\u3002<\/li>\n<li><strong>\u8d85\u952e\uff08Superkey\uff09<\/strong>\uff1a\u5173\u7cfb R \u7684\u4e00\u4e2a\u5c5e\u6027\u96c6 X\uff0c\u5982\u679c X \u80fd\u552f\u4e00\u5730\u6807\u8bc6\u5173\u7cfb R \u4e2d\u7684\u6bcf\u4e00\u4e2a\u5143\u7ec4\uff0c\u90a3\u4e48 X \u5c31\u662f\u4e00\u4e2a\u8d85\u952e\u3002<\/li>\n<\/ul>\n<h3>BCNF \u548c 3NF \u7684\u533a\u522b<\/h3>\n<ul>\n<li><strong>3NF\uff08\u7b2c\u4e09\u8303\u5f0f\uff09<\/strong>\uff1a\u4e00\u4e2a\u5173\u7cfb R \u6ee1\u8db3 3NF\uff0c\u5982\u679c\u5bf9\u4e8e\u5173\u7cfb\u4e2d\u7684\u6bcf\u4e00\u4e2a\u975e\u5e73\u51e1\u7684\u51fd\u6570\u4f9d\u8d56 X -&gt; Y\uff0c\u8981\u4e48 X \u662f\u4e00\u4e2a\u8d85\u952e\uff0c\u8981\u4e48 Y \u662f\u4e00\u4e2a\u4e3b\u5c5e\u6027\uff08\u5373\u5c5e\u4e8e\u67d0\u4e2a\u5019\u9009\u952e\u7684\u5c5e\u6027\uff09\u3002<\/li>\n<li><strong>BCNF\uff08\u535a\u4f0a\u65af-\u79d1\u5fb7\u8303\u5f0f\uff09<\/strong>\uff1a\u4e00\u4e2a\u5173\u7cfb R \u6ee1\u8db3 BCNF\uff0c\u5982\u679c\u5bf9\u4e8e\u5173\u7cfb\u4e2d\u7684\u6bcf\u4e00\u4e2a\u975e\u5e73\u51e1\u7684\u51fd\u6570\u4f9d\u8d56 X -&gt; Y\uff0cX \u90fd\u662f\u4e00\u4e2a\u8d85\u952e\u3002<\/li>\n<\/ul>\n<p>BCNF \u662f 3NF \u7684\u5f3a\u5316\u7248\u672c\uff0c\u56e0\u4e3a\u5b83\u8981\u6c42\u5bf9\u4e8e\u6bcf\u4e00\u4e2a\u51fd\u6570\u4f9d\u8d56 X -&gt; Y\uff0cX \u5fc5\u987b\u662f\u8d85\u952e\uff0c\u800c\u4e0d\u4ec5\u4ec5\u662f\u5141\u8bb8 Y \u662f\u4e3b\u5c5e\u6027\u3002<\/p>\n<h3>BCNF \u793a\u4f8b<\/h3>\n<p>\u8003\u8651\u4ee5\u4e0b\u5173\u7cfb\uff1a<\/p>\n<table>\n<thead>\n<tr>\n<th><strong>\u5b66\u751f\u8bfe\u7a0b\u8868<\/strong>\uff1a<\/th>\n<th>\u5b66\u751fID (StudentID)<\/th>\n<th>\u8bfe\u7a0b (Course)<\/th>\n<th>\u6559\u5e08 (Teacher)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>1<\/td>\n<td>\u6570\u5b66<\/td>\n<td>\u5f20\u8001\u5e08<\/td>\n<\/tr>\n<tr>\n<td>2<\/td>\n<td>\u7269\u7406<\/td>\n<td>\u674e\u8001\u5e08<\/td>\n<\/tr>\n<tr>\n<td>3<\/td>\n<td>\u5316\u5b66<\/td>\n<td>\u738b\u8001\u5e08<\/td>\n<\/tr>\n<tr>\n<td>1<\/td>\n<td>\u7269\u7406<\/td>\n<td>\u674e\u8001\u5e08<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h4>\u4e0d\u6ee1\u8db3 BCNF \u7684\u5173\u7cfb<\/h4>\n<p>\u5047\u8bbe\u6709\u4ee5\u4e0b\u51fd\u6570\u4f9d\u8d56\uff1a<\/p>\n<ol>\n<li>StudentID -&gt; Course, Teacher<\/li>\n<li>Course -&gt; Teacher<\/li>\n<\/ol>\n<p>\u5728\u4e0a\u8ff0\u5173\u7cfb\u4e2d\uff0c<code>Course -&gt; Teacher<\/code> \u8fdd\u53cd\u4e86 BCNF\uff0c\u56e0\u4e3a <code>Course<\/code> \u4e0d\u662f\u4e00\u4e2a\u8d85\u952e\uff08\u5b83\u4e0d\u80fd\u552f\u4e00\u5730\u6807\u8bc6\u5173\u7cfb\u4e2d\u7684\u6bcf\u4e00\u884c\uff09\u3002\u56e0\u6b64\uff0c\u8be5\u5173\u7cfb\u4e0d\u6ee1\u8db3 BCNF\u3002<\/p>\n<h4>\u6ee1\u8db3 BCNF \u7684\u5206\u89e3<\/h4>\n<p>\u4e3a\u4e86\u4f7f\u5173\u7cfb\u6ee1\u8db3 BCNF\uff0c\u53ef\u4ee5\u5c06\u5176\u5206\u89e3\u4e3a\u4e24\u4e2a\u5173\u7cfb\uff1a<\/p>\n<table>\n<thead>\n<tr>\n<th><strong>\u5b66\u751f\u8bfe\u7a0b\u8868<\/strong>\uff1a<\/th>\n<th>\u5b66\u751fID (StudentID)<\/th>\n<th>\u8bfe\u7a0b (Course)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>1<\/td>\n<td>\u6570\u5b66<\/td>\n<\/tr>\n<tr>\n<td>2<\/td>\n<td>\u7269\u7406<\/td>\n<\/tr>\n<tr>\n<td>3<\/td>\n<td>\u5316\u5b66<\/td>\n<\/tr>\n<tr>\n<td>1<\/td>\n<td>\u7269\u7406<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<table>\n<thead>\n<tr>\n<th><strong>\u8bfe\u7a0b\u6559\u5e08\u8868<\/strong>\uff1a<\/th>\n<th>\u8bfe\u7a0b (Course)<\/th>\n<th>\u6559\u5e08 (Teacher)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>\u6570\u5b66<\/td>\n<td>\u5f20\u8001\u5e08<\/td>\n<\/tr>\n<tr>\n<td>\u7269\u7406<\/td>\n<td>\u674e\u8001\u5e08<\/td>\n<\/tr>\n<tr>\n<td>\u5316\u5b66<\/td>\n<td>\u738b\u8001\u5e08<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>\u73b0\u5728\uff0c<code>\u5b66\u751f\u8bfe\u7a0b\u8868<\/code> \u548c <code>\u8bfe\u7a0b\u6559\u5e08\u8868<\/code> \u90fd\u6ee1\u8db3 BCNF\uff1a<\/p>\n<ul>\n<li>\u5728 <code>\u5b66\u751f\u8bfe\u7a0b\u8868<\/code> \u4e2d\uff0c\u6ca1\u6709\u4efb\u4f55\u975e\u5e73\u51e1\u7684\u51fd\u6570\u4f9d\u8d56\uff08<code>StudentID<\/code> \u662f\u8d85\u952e\uff09\u3002<\/li>\n<li>\u5728 <code>\u8bfe\u7a0b\u6559\u5e08\u8868<\/code> \u4e2d\uff0c<code>Course<\/code> \u662f\u8d85\u952e\u3002<\/li>\n<\/ul>\n<h3>\u603b\u7ed3<\/h3>\n<p>BCNF \u662f\u4e00\u79cd\u5173\u7cfb\u6570\u636e\u5e93\u89c4\u8303\u5316\u5f62\u5f0f\uff0c\u7528\u4e8e\u6d88\u9664\u5197\u4f59\u6570\u636e\uff0c\u786e\u4fdd\u6570\u636e\u4e00\u81f4\u6027\u3002\u901a\u8fc7\u5c06\u5173\u7cfb\u5206\u89e3\u4e3a\u6ee1\u8db3 BCNF \u7684\u5b50\u5173\u7cfb\uff0c\u53ef\u4ee5\u907f\u514d\u5197\u4f59\u6570\u636e\u548c\u66f4\u65b0\u5f02\u5e38\uff0c\u4ece\u800c\u63d0\u9ad8\u6570\u636e\u5e93\u7684\u6027\u80fd\u548c\u6570\u636e\u5b8c\u6574\u6027\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>BCNF\uff0c\u5168\u79f0\u4e3a Boyce-Codd Normal Form\uff08\u535a\u4f0a\u65af-\u79d1\u5fb7\u8303\u5f0f\uff09\uff0c\u662f\u5173\u7cfb\u6570\u636e\u5e93\u4e2d\u7684\u4e00\u79cd\u89c4\u8303\u5316&#8230; <\/p>\n<div class=\"read-more navbutton\"><a href=\"https:\/\/t.n-years.com\/?p=6372\">\u9605\u8bfb\u66f4\u591a<i class=\"fa fa-angle-double-right\"><\/i><\/a><\/div>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[123],"tags":[108],"class_list":["post-6372","post","type-post","status-publish","format-standard","hentry","category-123","tag-108"],"_links":{"self":[{"href":"https:\/\/t.n-years.com\/index.php?rest_route=\/wp\/v2\/posts\/6372","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/t.n-years.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/t.n-years.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/t.n-years.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/t.n-years.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=6372"}],"version-history":[{"count":1,"href":"https:\/\/t.n-years.com\/index.php?rest_route=\/wp\/v2\/posts\/6372\/revisions"}],"predecessor-version":[{"id":6373,"href":"https:\/\/t.n-years.com\/index.php?rest_route=\/wp\/v2\/posts\/6372\/revisions\/6373"}],"wp:attachment":[{"href":"https:\/\/t.n-years.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6372"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/t.n-years.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6372"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/t.n-years.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6372"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}