Path: utzoo!attcan!uunet!dev!dgis!jkrueger
From: jkrueger@dgis.dtic.dla.mil (Jon)
Newsgroups: comp.databases
Subject: Re: Relational Database, with a Graphical type field
Keywords: Database to store/handle Graphics
Message-ID: <902@dgis.dtic.dla.mil>
Date: 28 Jun 90 20:50:25 GMT
References: <1176@abcom.ATT.COM> <897@dgis.dtic.dla.mil> <882@rm1.UUCP>
Organization: Defense Technical Information Center (DTIC), Alexandria VA
Lines: 29

bapat@rm1.UUCP (Bapat) writes:

>>>	...file name as string, reference to graphical file

>>Then no atomic, serializable updates.  Is this OK?

>Why is that? Why can I not update the graphical field atomically?

How do you roll back an update to a file?

>If I'm only doing single-transaction updates, why would serializability
>be a concern?

1) other users doing concurrent updates
2) why give up transactions?  you lose atomic updates to
structured data

>one couldn't say 
>   "select mug_shot from employee where <the employee wears glasses>."

In the sense that such operations aren't defined on unstructured BLOBs,
indeed on couldn't.  But there are ways of defining them on data types;
in fact, the data type is defined by the operation.  A useful graphical
data type is one on which one can select by graphic features.

-- Jon
-- 
Jonathan Krueger    jkrueger@dtic.dla.mil   uunet!dgis!jkrueger
Drop in next time you're in the tri-planet area!