David Tangye wrote: > > > On 5/30/07, *Chris Travers* <[EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>> wrote: > > Ok. Think of an entity as a "legal person" (corporate or natural) and > a contact as a "natural person." > > > Yes, I assume that a 'Contact' is a contact for an Entity. So Chris > Travers can be the contact for Chris Travers. As a physical design issue > you might consider Name on Contact to be NULL, or conversely redundantly > store the same data value for Name on Entity and Contact.
Actually an Entity is considered the "common name". Not the legal name. A person or a company is where you would derive the legal person. For example: Entity: Josh Drake Person: Joshua David Drake > > The idea is that each entity has one > primary class and may have many auxiliary classes. So an entity can > be a customer, a vendor, etc. all at once. > > > Fine. You just need to decide on a similar physical design issue as > above, once you get to the physical model, ie do you store the primary > class in the intersect table to Class as well as in the Entity table. Primary class is defined by the entity_class column that is a foreign key. E.g; that defines the entity as a Vendor. Secondary classes are defined by a many to many look up table and thusly you can have a Vendor, who sometimes is a customer. > > > 2. The term and term fragment "class" (assuming it means "our way of > > classifying the entities") might be better understood using the term > > and term fragment "role". Term fragments class/group/type are all > > shallow terms in entity/logical modelling. What we want to know > is WHY > > we are classifying/grouping/typifying an entity. > > Think of possible classes as any of (lead, customer, vendor, member, > any that might be added later). > > > As long as the later values are mutually exclusive, otherwise it is > merging types of classifications into one modelling entity (called > 'class'), and is going to cause grief. In fact its a basic no-no in > modelling. > > I tend to think of "role" as being > somethign that defines what something defines what something does, Role is for security not for definition of types of entities. Thus I agree with Chris above. > > > Yes, like 'Sell', ie a vendor, or 'Buy' ie a customer. That is what I am > saying. Except that it is not. Sell is a task performed just as Buy is. A vendor or customer is a class of entity. > I do not think Class is a term that application end-users would so > readily relate to. Then again, I am probably continuing to think of > end-users as not being software-techoes, and this is a difference I > think we have argued before. > > At the end of the day I am sure you will build an application that makes > sense to yourself. And others except you ;). This designed has been vetted already with customers. Sincerely, Joshua D. Drake > > Cheers > David > > -- > The Last Great Frontier is in Your Mind > > > ------------------------------------------------------------------------ > > ------------------------------------------------------------------------- > This SF.net email is sponsored by DB2 Express > Download DB2 Express C - the FREE version of DB2 express and take > control of your XML. No limits. Just data. Click to get it now. > http://sourceforge.net/powerbar/db2/ > > > ------------------------------------------------------------------------ > > _______________________________________________ > Ledger-smb-devel mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/ledger-smb-devel -- === The PostgreSQL Company: Command Prompt, Inc. === Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240 Providing the most comprehensive PostgreSQL solutions since 1997 http://www.commandprompt.com/ Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate PostgreSQL Replication: http://www.commandprompt.com/products/ ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Ledger-smb-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/ledger-smb-devel
