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From "Fredrik Rubensson" <>
Subject RE: Concept for modeling hierarchical data
Date Tue, 10 Jan 2006 15:20:30 GMT

Florian Lindner wrote:
> > Florian Lindner wrote:
> > >Hello,
> > >I'm searching for the best concept of how to use and save 
> > >hierarchical  data. I have a structure like PC file system with
> > >data. There a  folder objects and files objects of different types.

> > >Every object have  data like permissions, date and author. And they

> > >have type-specific data  fields like resolution (of an image type)
> > >location (of an meeting
> > > type) or ingredients (of an recipe type).
> > >What is the best way to store that kind of data? What database is 
> > >recommendable? What concepts of persistance? Or not using managed  
> > >persistance and do it manually?
> >
> > If you want to do it manually, a hierarchical tree can be
> > by just one table:
> >
> > CREATE TABLE tree (
> >     id   INTEGER   PRIMARY KEY,
> >     parent_id   INTEGER
> > );
> >
> > With managed persistence, be carefull not to configure it to load
> > entire tree at once.
> >
> > As for a DB, any decent relational DB will do.
> In this concept I need a table for every type of objekt I want?

It depends on if you want the DB to handle data integrity for you. If
you are happy to have everything as key-value pairs you can come away
with two tables. Add a table with columns kay, values and a foreign key
to the suggested tree table. If you want specific data integrity per
type you will have to have one table per type. It also seems that some
data is there for all types (permissions, date and author). Maybe you
want to reuse that definition in one table. 

In the end it depends on what you will be using this tree of data for,
how will you access it and what technology will be used? Will it be
read-only or both reads and writes? Volumes? Number of users? If data is
to be updated by several users I think youl should definitely use a
relational database of some kind. If it is read-only then XML files will
be good enough. Hibernate is a good persistence framework to use if you
want to do the modeling in XML or Java.


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