Finding Entties尋找實體

1、finding entitieswhat is an entitynan entity is a person, place, object, event, or concept about which the organization wishes to record data.nentities should be things that are readily recognized by anyone working in the enterprise.some entity rulesan entity1. must be within the scope of the system2

2、. must have at least one non-key attributewhere to beginnto begin, we must have some form of information that we can use in our analysis. ncollect information about the major business functions and processes.nwe can use questionnaires, interviews, observations etc. where to beginnanother good source

3、 of information for data modeling can be obtained by collecting any forms that are used by the enterprise.nthese forms provide valuable information on what data is important to the enterprise and how it is grouped.where to beginnonce we have a concise picture of the processes we are going to model,

4、we can begin the iterative process of finding the entities that are necessary to support the enterprise.the steps involved1. identify the system informationa. user interviewsb. paper and screen documentsc. previous system documentationthe steps involved2. identify entitiesa. analysis of english gram

5、mar -entity-relationship diagramsb. heuristicsc. normalization processanalyze the grammernusing the table on the next slide, find the entities, attributes and relationships from the description and other information we have gathered about the enterprise. use this table to startenglish (if the word i

6、s a)erd (on the erd we will show)proper nounentity (“name” of an entity)common nounentity or entity-typetransitive verbm-ary relation (m1)intransitive verbunary relationship or attribute valueadjectiveattribute of an entityadverbattribute of a relationshipsentence restructuringnext we do some senten

7、ce restructuring:convert any sentence in the following form:“there are . . . x in y”into“y has . . . x”sentence restructuring example“there are more than 200 employees in every department.” “every department has more than 200 employees.”xyxymore restructuringif the english sentence says, “the x of y

8、 is z”y is an entityx is either an attribute or an entity,depending on what type of “z” it is.if “z” is a proper noun, then x is arelationship between y and zotherwise, x is an attribute of ymore examplesthe birthdate of the student is 10/22/71. (x) (y) (z)attribute entity not a proper nounthe advis

9、or of john smith is dr. greene. (x) (y) (z)relationship entity proper noun candidate entitiesnthe preceeding steps have provided a list of candidate entities. now we need to apply a few more rules to ensure we have only those entities that are essential to the enterprise.paring down the listnfirst,

10、eliminate any duplicate entities. these can be entities with different names but representing the same thing. for example patron and customer. these may both represent the same entity.nsecond, eliminate and entities that are not important to the enterprise. this may require some analysis and work wi

11、th the user/end customer.now add some heuristicswhen is an entity an entity?nany entity with only one evident instance (e.g. the national basketball league, nhl, nfl etc.) is not a good entity because it is modeling business context or the business itself.nif one entity is in the center of everything and is connected to everything else it is probably the view point or context rather than an entity.finelyremember tha