Essay about Crows Foot - 1438 Words
Crow?s Foot Notation
Crow?s Foot Notation
A number of data modeling techniques are being used today. One of the most common is the entity relationship diagram (ERD). Several ERD notations are available. For the purposes of CS270 we will be using Crow?s Foot Notation[b1].
Components used in the creation of an ERD:
Entity ? A person, place or thing about which we want to collect and store multiple instances of data. It has a name, which is a noun, and attributes which describe the data we are interested in storing. It also has an identifier, which uniquely identifies one instance of an entity. The attribute which acts as the identifier is marked with an asterisk. ?
Relationship ? Illustrates an association between two entities. It has a name which is a verb. It also has cardinality and modality. ????????
Cardinality and Modality are the indicators of the business rules around a relationship. Cardinality refers to the maximum number of times an instance in one entity can be associated with instances in the related entity. Modality refers to the minimum number of times an instance in one entity can be associated with an instance in the related entity. Cardinality can be 1 or Many and the symbol is placed on the outside ends of the relationship line, closest to the entity, Modality can be 1 or 0 and the symbol is placed on the inside, next to the cardinality symbol. For a cardinality of 1 a straight line is drawn. For a cardinality of Many a foot with three toes is drawn. For a modality of 1 a straight line is drawn. For a modality of 0 a circle is drawn.
??????? ????????
?zero or more [b4] ?1 or more [b5]
www2.cs.uregina.ca/~bernatja/crowsfoot.html
Crow?s Foot Notation
? ????????
?1 and only 1 (exactly 1) [b6]
?zero or 1 [b7]
Cardinality and modality are indicated at both ends of the relationship line. Once this has been done, the relationships are read as being 1 to 1 (1:1), 1 to many (1:M), or many to many (M:M).
??????????????????????????????????? 1:1
??????????????????????? 1:M
??????????????????????? M:M
??????????????????????? 1:M
Typically, ERDs are much more complex than this, involving quite a number of entities and relationships. If we join all of the above relationships together and add a few attributes, a small collection of data might be depicted in the following way using Crow?s Foot Notation:
www2.cs.uregina.ca/~bernatja/crowsfoot.html
Crow?s Foot Notation
Consider the following business rules for a patient appointment system: A doctor can be scheduled for many appointments, but may not have any scheduled at all. Each appointment is scheduled with exactly 1 doctor. A patient can schedule 1 or more appointments. One appointment is scheduled with exactly 1 patient. An appointment must generate exactly 1 bill, a bill is generated by only 1 appointment. One payment is applied to exactly 1 bill, and 1 bill can be paid off over time by several payments. A bill can be outstanding, having nothing yet paid on it at all. One patient can make many payments, but a single payment is made by only 1 patient. Some patients are insured by an insurance company. If they are insured, they can only carry insurance with one company. An insurance compnay can have many patients carry their policies. For patients that carry insurance, the insurance company will make payments, each single payment is made by exactly 1 insurance company. Given the above information, the following ERD can be drawn:
www2.cs.uregina.ca/~bernatja/crowsfoot.html
Crow?s Foot Notation
Intersection Entities Intersection entities are used in the resolution of a many to many relationship. This resolution is done in order to store additional information which doesn?t fit into the attribute list of either entity in the M:M relationship. For instance, in the...
Please join StudyMode to read the full document
1489 Words
1400 Words
1000 Words
1026 Words
1475 Words
Become a StudyMode Member当前位置： &
crowfoot中文是什么意思
名词复数: crowfeet&&&
中文翻译1.(pl. -foots) 【植物；植物学】毛莨(属)；玉柏；牛角花；臭荠状车前；老鹳草(属)。2.(pl. -feet) 【军事】铁蒺藜，拦路钩；【摄影】防滑三角架。3.(pl. -feet) 【航海】吊索。&&&&匍枝毛茛... &&&&&&爪形扳手... &&&&&&带拔钉子叉头的大撬杠... &&&&&&爪形细裂... &&&&&&爪形裂缝... &&&&&&爪形皱裂... &&&&&&天幕吊索; 天幕索... &&&&&&将盖子固定在搭板上的叉子... &&&&&&爪形镇压器... &&&&&&爪形镇压器... &&&&&&土耳其缎... &&&&&&爪形扳手... &&&&&&块扳手... &&&&&&水毛莨... &&&&&&袋草... &&&&&&鸟足状水系... &&&&&&爪子扶正阀... &&&&&&将盖子固定在塔板上的叉子... &&&&&&爪形纵裂缝... &&&&&&单头扳手... &&&&&&撬棍... &&&&&&桃乐丝?克劳福特?霍奇金... &&&&&&常春藤毛茛。 ... &&&&&&花毛茛... &&&&&&毛茛... &&&&&&克罗菲尔德... &&
关注微信公众号：chachacidian，即可查询单词
例句与用法3 8 " 15 pc crowfoot wrench set 14 pcs ribe power bit set3 8 ”单开口牛啼工具组15件14 pc 1 2 " drive open - end crowfoot wrench set1 2 ”单开口牛啼工具组14件3 8 " 15 pc crowfoot wrench set3 8 ”单开口牛啼工具组15件Wrench , crowfoot attachments扳手及爪形附件Crowfoot longitudinal crack爪形纵裂缝There the water -
the crowfoot here . either the change in the quality of the air from heavy to light , or the sense of being amid new scenes where there were no invidious eyes upon her , sent up her spirits wonderfully也许是空气的性质从沉闷到轻松的变化，也许是她觉得已经到了没有人用恶意的眼光看待她的新地方，于是她的精神奇妙地振作起来。 Men had been cutting the water - weeds higher up the river , and masses of them were floating past her - moving islands of green crowfoot , whereon she might long locks of which weed had lodged against the piles driven to keep the cows from crossing工人们已经开始在河流的上游割水草了，一堆一堆的水草从她面前漂过去就像是绿色的毛茛小岛在移动，她差不多就可以站在上面了河里栽有一排一排木桩，是为了防止奶牛跑过河去，这时挡住了流下来的水草。 &&
英文解释any of various plants of the genus Ranunculus同义词：, , , , ,
百科解释Crowfoot (c.
? 25 April 1890) or Isapo-Muxika (Blackfoot Issapóómahksika, &Crow-big-foot&blkft.详细百科解释
相邻词汇热门词汇
crowfoot的中文翻译，crowfoot是什么意思，怎么用汉语翻译crowfoot，crowfoot的中文意思，，，，发音，例句，用法和解释由查查在线词典提供，版权所有违者必究。
&&&&&&&&&&&&&&&&
Copyright &
(京ICP备号)
All rights reserved 上传我的文档
 下载
 收藏
长期从事金融分析，国际金融前沿信息研究，在金融分析方面具有一定的经验和资料的积累，希望能够遇到互相帮助的朋友
 下载此文档
正在努力加载中...
Crow’s Foot Notation - Simmons College：乌鸦的脚符号-西蒙斯学院
下载积分：2500
内容提示：Crow’s Foot Notation - Simmons College：乌鸦的脚符号-西蒙斯学院
文档格式：PDF|
浏览次数：94|
上传日期： 23:15:18|
文档星级：
全文阅读已结束，如果下载本文需要使用
 2500 积分
下载此文档
该用户还上传了这些文档
Crow’s Foot Notation - Simmons College：乌鸦的脚
关注微信公众号}