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Conference ulysse::rdb_vms_competition

Title:DEC Rdb against the World
Moderator:HERON::GODFRIND
Created:Fri Jun 12 1987
Last Modified:Thu Feb 23 1995
Last Successful Update:Fri Jun 06 1997
Number of topics:1348
Total number of notes:5438

215.0. "Referential Int. for DB2?" by CLO::MOLLEY () Wed Oct 12 1988 16:09

    G'day,
    
    IBM will soon (or already has) announced that the latest version
    of DB2 will support referential integrity (something their users
    have been clamoring about for awhile).  They (IBM) qualified this
    enhancement by saying that it applies to foreign keys only.
    
    Now I know what a foreign key is, but I'm somwhat confused by this
    qualifying remark.  Any explanations would be appreciated.
    
    Regards,
    Nik
T.RTitleUserPersonal
Name		DateLines
215.1My best guess ...GUIDUK::KRUGAnswer in the form of a question.Thu Oct 13 1988 23:3924
    Nik,

    That is a confusing comment.  I would probably take it to mean that
    only when a foreign key value is updated or inserted would R.I.
    checking be invoked.  Updating or deleting a primary key would not
    invoke any checking.  If this is what IBM means, it's not too
    impressive. 
    
    "Supporting" referential integrity is a little vague, too.  Rdb
    constraints SUPPORT R.I. in that they detect the violation condition.
    They don't totally implement R.I. in that they don't take specified
    actions (e.g., NULLIFIES, CASCADES).  They take only the action
    "RESTRICTS." 
    
    A DBMS couldn't totally implement R.I. without understanding primary
    and foreign keys of the USER relations.  (DB2 has understood these keys
    for SYSTEM tables from 1.0).  It sounds like DB2 will have to at
    least understand these keys now.
    
    I don't know, that's just my shot at it.  I usually have trouble
    understanding what IBM really means anyway.
    
    Paul Krug
215.2guesses welcome...CLO::MOLLEYFri Oct 14 1988 01:428
    Paul,
    
    Thanks for your insight.  As you say, IBM is usually vague on many
    of their comments.
    
    Regards,
    Nik
215.3Not yet, but soon.COOKIE::JANORDBYFri Oct 14 1988 20:4916
    Initially, IBM announced full referential integrity, including
    primary/foreign key support as well as cascading delete and null
    support. However, two or three months after initial announcement,
    industry consultants began reporting that cascading deletes will
    no be supported initially. I have not yet heard what the technical
    problem was that is holding it up.
    
    I don know that the target date for DB2 Version 2 was set 3 or 4
    years ago based primarily upon the time it would take to do referential
    integrity. The performance and other features were the 'other' things
    that were also possible during the same time. Even if the initial
    release does not support full RI, it is just around the corner.
    In comparison, Rdb can detect RI violations, but cannot yet do the
    cascading either.
    
    Jamey