Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

paul c schrieb: 
Jan Hidders wrote:


Another small thing is updating primary keys. If a primary key has accidentally been entered wrong and you want to fix that with an update then it is usually not possible to simply update it, and the problem gets even worse if it is also refered to by foreign keys. In an ER model this is a non-problem.


like a few other people (i suspect we are a minority), i think of 'update' as a sugaring or shortcut. ignoring transaction or concurrency issues, is there any logical difference between 'update' and the combination of 'delete-insert'? (granted the latter implies an operator sequence which is why i ignore concurrency issues.)

Update and delete-insert should be fundamentally different operations for the following reason. Update deals with object semantics, i.e., how they are characterized by other *existing* objects. In particular, update does not change the number of objects and their references. Delete-insert is a life-cycle management operation that has nothing to do what objects mean. Instead, it creates or deletes references, which reflect object existence. As I already mentioned somewhere in this forum we need to distinguish two layers:
- object semantics (field values), and
- object representation (references).
If they are not separated like in the RM then there is no need to separate the operations of update and delete-insert (at fundamental level). Thus in the RM, I agree, these two operations are quite comparable. But in this case we have numerous problems. One of them is updating primary key (which has to be disabled in a good model). However, if we want to separate these two layers then these operations are fundamentally different.

--
http://conceptoriented.com
.

Relevant Pages

  • Re: Further advice on assembling books
    ... What I'm talking about is using symbols to identify endnotes. ... documents for those particular references. ... about whether to produce a book as a single file or separate chapters ... If he uses automatic numbering: ...
    (microsoft.public.word.docmanagement)
  • Re: Normalization
    ... My structure is like you describe (separate tables, ... The problem I am having trouble with is JobTitle. ... Because suggest related references be kept ... field in tblJobs called Status which would be modified at each stage and the ...
    (microsoft.public.access.tablesdbdesign)
  • RE: Search form for multiple fields
    ... to address the separate "Author" table. ... publication (as I have several hundred publications ahead of me -- I'd like ... parameter and, to make the selections optional, test for Nulls, so the query ... table of technical references in a database. ...
    (microsoft.public.access.gettingstarted)
  • Re: Does Codds view of a relational database differ from that ofDate&Darwin?[M.Gittens]
    ... Update deals with object semantics, i.e., how ... > update does not change the number of objects and their references. ... > Delete-insert is a life-cycle management operation that has nothing to ... There are advantages and disadvantages to distinguishing between ...
    (comp.databases.theory)
  • Re: Kensington runestone in the Scandinavian press
    ... >>only a dim memory across 5+ years of encountering two separate ... >>references to two separate finds. ...
    (sci.archaeology)