Hi Stephen, I put some comments/arguments for this (current) decision onto the relational model twiki page (https://twiki.cern.ch/twiki/bin/view/EGEE/ExampleGlue20SQL). Generally, there are two extrems for modelling a db schema: One is that you push everthing into one huge table with key-type-value colums (which is the most flexible solution) and the other one is to model all entites having every multivalued attributes/entity explicit in a child table. This implies a lot of joins over several tables which affects quite heavily the usability. The Endpoint in the current schema for example, would have another set of 4 child tables. For sure, if you want to model everything in detail and nicely normalized - this is the solution. I am currently not really convinced this is neccessary. Someone may tell me better.. Also, inserting/updating data for several tables is a more heavy-weight operation than for say, two tables. Consider that the DB systems needs to update more index files. I've spoken with some DB admins from CERN and they confirmed that look-ups within one table are quite (very) fast which supports the argument of putting some attributes into this ValueTable. I've done this concept with the current schema (1.3) as well and here the MultiValued table has around 120K entries (I would claim this as easy work for modern DB systems - e.g. Google uses MySQL in !much! larger scale). It has the advantage of allowing queries to be quite easy (less joins), providing some schema flexibility at the same time. At the time when I created this relational model (3 weeks ago :-) )we had more multivalued attributes (each resulting in a child table) in the schema. This fact, however, might have changed and I may reevaluate this decision. Thinking about this, I would propose to try a mix-solution: all multivalued attributes of one entity (say Endpoint) go into ONE child table (not 4). I would also like to influence Timo's experience into this decision since they currently try to write a info provider for the proposed schema. Cheers, Felix --- Felix Ehm IT-GD tel : +41 22 7674580 CERN, Switzerland -----------------------------------------
-----Original Message----- From: glue-wg-bounces@ogf.org [mailto:glue-wg-bounces@ogf.org] On Behalf Of Burke, S (Stephen) Sent: Montag, 14. April 2008 18:09 To: Felix Nikolaus Ehm; glue-wg@ogf.org Cc: Steve Fisher; a.j.wilson@rl.ac.uk; timo.baur@lrz-muenchen.de Subject: Re: [glue-wg] Update of relational rendering of Glue 2.0 draft 33
[mailto:glue-wg-bounces@ogf.org] On Behalf Of Felix Nikolaus Ehm said: please find the latest rendering for the relational model (ref 33) here: https://twiki.cern.ch/twiki/bin/view/EGEE/ExampleGlue20SQL
Unfortunatly, I didn't find time to update the examples on
glue-wg-bounces@ogf.org the page -
but its on my list.
Comments/Questions are appreciated.
Have you had comments from Steve Fisher or Antony Wilson, who did the R-GMA implementation [1] in the past? I think they're on the glue list but they may not be paying attention ...
One comment is that your proposal to have all multivalued attributes in one huge table doesn't seem very good to me. Why do you rule out having separate tables for each attribute? That is basically how it's done in R-GMA at the moment.
Stephen
[1] See e.g. https://eg.nikhef.nl:8443/R-GMA/table.html _______________________________________________ glue-wg mailing list glue-wg@ogf.org http://www.ogf.org/mailman/listinfo/glue-wg