Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!ncrlnk!ncrwic!cetc!sjohnson From: sjohnson@cetc.Wichita.NCR.COM (Steve Johnson) Newsgroups: comp.databases Subject: Entity Supertypes/Subtypes & SQL Message-ID: <1015@cetc.Wichita.NCR.COM> Date: 13 Apr 89 19:31:11 GMT Reply-To: sjohnson@cetc.UUCP (Steve Johnson) Organization: NCR Corporation, Wichita, Kansas Lines: 53 >In message <1011@cetc.Wichita.NCR.COM>, sjohnson@cetc.Wichita.NCR.COM writes: >>I am looking for a solution to the following entity >>supertype/subtype problem. >[Example of Purchase Orders dealing with > items - seems a variation on the Factory Model - see below] >As is, this seems to be a factory tracking type of problem which the >relational model cannot directly handle (the factory tracking model is >one that given an end product produce a list of resources that went into >it - a very complex outer join with incomplete information). Perhaps the >model you are working with can be rethought into something more >appropriate for the relational model. Your right in that the application I am working on involves the tracking of integrated circuits through various workstations collecting various test data. >The problem requires some tradeoffs. With the relations as defined, it >is fairly easy to design applications that can determine PO for minerals, >etc., but it is very difficult to get information about a PO of a certain >date. The connections between relations are dependent upon values of >tuples within relations. The relational model supports fixed >relationships. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^ Isn't this rather large problem with the relational model considering that Entity Supertypes/Subtypes are as I see it rather common. Or was the relational model intended to be this way? >>Steve Johnson | Information Systems & Services, NCR-CETC 530-4726 >David Masterson >DMasterson@cup.portal.com Does anyone have any neat routines written out there in Oracle using cursors that handle querying different tables based on the result of a column in a table? -- Steve Johnson | Information Systems & Services, NCR-CETC 530-4726 (316)636-4726 | Component Evaluation Technology Center 3450 N. Rock Rd. | Wichita, KS 67226 |