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From: wlrush@water.waterloo.edu (Wenchantress Wench Wendall)
Newsgroups: ont.events,uw.talks,uw.cs.grad
Subject: DATA BASES SEMINAR
Keywords: Professor Opher Etzion, Temple Univ.
Message-ID: <2801@water.waterloo.edu>
Date: 1 Dec 89 14:28:08 GMT
Distribution: ont
Organization: U of Waterloo, Ontario
Lines: 85


DEPARTMENT OF COMPUTER SCIENCE
UNIVERSITY OF WATERLOO
SEMINAR ACTIVITIES

DATA BASES SEMINAR

                    -Thursday, December 7, 1989

Professor  Opher  Etzion, Temple University, will speak
on ``PARDES - An Enhanced Active Database System.''

TIME:                 3:30 p.m.

ROOM:                 DC 1302

ABSTRACT

Traditional databases are passive. They do only what is
explicitly  requested  in  the  user's  query or update
operation.The  active  database  paradigm states that a
database may react in an intelligent way to an external
input  by  creating  and executing database operations,
which, though not explicitly requested in the input,are
required  to preserve invariants associated to the data
base.

This  paradigm  replaces  many operations traditionally
implemented  by  application  programs with descriptive
definitions that are part of the data model.

There  are  some  implementations of this paradigm. The
most notable are POSTGRES, HiPAC, SAPIENS.  Most of the
implementations  are  TRIGGER- ORIENTED. While triggers
are   flexible,   it   is  very  difficult  to  control
interrelationship between triggers. Our model employs a
different   app-   roach   which  extends  the  current
implementations in the following ways:

1.  It  increases  the expressive-power of the language
    used to  define the database schema by allowing the
    specification   of    a  richer class of invariants
    (stated   as   equations)       than  is  currently
    supported. Example:[SALARY := BASE-SALARY + BONUS +
    1000* count(SUBORDINATES)] The proposed language is
    compact  yet  powerful.   It  reduces  the  cost of
    development   and  maintenance  of  database update
    applications and reduces the problems of validation

                   November 30, 1989

                         - 2 -

    and verification thus  improving reliability.

2.  It  provides  an efficient algorithm for generating
    the  auxiliary  operations required to preserve the
    invariants  after      an   update [In other models
    these  operations  have   to  be  explicitly coded,
    either   in  the  application  program  or  in  the
    database schema.]

3.  It  provides  a  control  algorithm that guarantees
    minimum   updates   in the database per transaction
    as well as a deterministic update sem- antics.

4.  Existing   models   handle   exceptions  either  by
    disallowing  them,  or  by  requiring  the  user to
    specify   exception-handling   routines  for    any
    exception.     Our  model  introduces the notion of
    Exception-Handling  Mode, proposes a number of such
    modes,   and  specifies how modes can be defined in
    the  data  base  schema.    [ An exception handling
    mode  represents  a  general  method for handling a
    class  of  exceptions.    ]  The  modes  we propose
    eliminate   a   large   portion  of  the exception-
    handling  code that currently exists in application
    programs.

In  the  talk  I  will  briefly  survey the motivations
behind  the  active  databases discipline, and refer to
some related work.   The properties of the PARDES model
mentioned above will be presented using   examples.

                   November 30, 1989


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