Data Management（资料管理）课件.ppt

Relationship: By Example(4) Each STUDENT may be enrolled in one or more COURSEs Each COURSE may be taken by one or more STUDENT enrolled in taken by COURSE STUDENT 精品文档 Relationship: Exercise issued for Bought via CUSTOMER ORDER PROD_ITEM WAREHOUSE originated by the originator of stored in the repository for 精品文档 Each ORDER must be issued for one or more PROD_ITEMs Each PROD_ITEM may be bought via one or more ORDER Each ORDER must be originated by one and only one CUSTOMER Each CUSTOMER may be the originator of one or more ORDER Each PROD_ITEMs must be stored at one and only one WAREHOUSE Each WAREHOUSE may be the repository of one or more PROD_ITEMs Relationship: Solution 精品文档 One-to-one rare mandatory in both directions is very rare. may be the same entity. many-to-one very common mandatory in both directions is rare many-to-many very common Relationship Type 精品文档 Determine the existence of a relationship. Name each direction of the relationship. Determine the optionality of each direction. Determine the degree of each direction. Validate it. Analyze And Model Relationship 精品文档 based on bought from description of operated by represented by responsible for the basis for the supplier of for the operator for the representation of the responsibility of Useful Relationship Name Pairs 精品文档 Entity Box 向上對齊。 Relationship lines 儘量以直線表示，若不得不為斜線，角度應在30o ~ 60o之間。 雞爪(crowsfoot) 儘量放在左(上)方的位置。 較大的Entity Box (attributes多者)儘量放在左(上)方的位置儘量放在左(上)方的位置。。 所有的 relationship 都要以文字描述。 Layout of the E-R Diagram 精品文档 Attributes are information about an entity that needs to be known。 Attributes describe、classify 、quantify or express the state of the entity Attributes STUDENT id name phone address blood_type 來自需求 精品文档 將 Attribute 的意義拆解至較簡單的型式。 Determine Attributes(1) STUDENT id name phone address blood_type addr_city addr_county addr_street addr_zip 精品文档 Data Management(資料管理) Employ database development approach to transfer business information