Re: data modelling, ER diagram
Date: Wed, 16 Sep 1992 17:37:01 GMT
Message-ID: <1992Sep16.173701.8195_at_cs.sfu.ca>
In article <11SEP199212091688_at_watson.bms.com> sinha_at_watson.bms.com (Anil Sinha) writes:
>Heres a question for data modellers.
>
>How does one incorporate the restriction that a given relation is a subset of
>another relationship ?
>
>Assume we have these entities:
>
>Grant: Approved grants
>Party: Parties working on grants
>Payments: payments made to parties
>
>There is another entity "grant and party" which shows many to many
>relationship between grant and party. The entity payment is payment to a party
>and could be made against many grants. So there is another entity "payment and
>grant" which shows many to many relationship between payment and grant.
>So a given payment to party should be made against grants which are valid within
>the entity "grant and party" for the given party. Can this restriction be
>modelled within the ER diagram ?
>
How about this?
(Deduction) (Payment)
________ ________ _________
|Grant &| | | | |
|Party &|\ |Party &|\ | |
| Date |-------------------------| Date |----| Date |
| |/ | |/ | |
--------- --------- ---------
\|/ \|/
| |
| |
>|-------|(Authorization) |-----------------|
>| | | |
>|Grant |\ | |
>|and |---------------------| |
>|Party |/ | Party |
>| | | |
>|-------| ------------------
\|/
> |
> .
> .
>|-------|
>| |
>|Grant |
>| |
>|-------|
>
An authorization permits certain parties to receive monies from certain grants. A Payment is made to a given party on a given date. A Deduction specifies the amount to be charged to a given grant for a given payment via ensuring that the party to whom the payment is to be made has been authorized to receive monies from the grant which is to be charged.
-- Gary Hall | Voice (604) 291-3208 | INTERNET: hall_at_cs.sfu.ca Centre for Systems Science | Fax (604) 291-4951 | BITNET: hall%cs.sfu.ca_at_ Simon Fraser University | | relay.cdnnet.ca Burnaby, B.C. V5A 1S6 |Received on Wed Sep 16 1992 - 19:37:01 CEST