michael munson wrote: > Greetings, > I'm a bit new to SQL and SQLite so pardon me if I ask silly questions but I > have run into a bit of a wall while attempting to design a database for a C++ > program I am attempting to write. > > The needs of the database are to: represent an object oriented hierarchy of > any number of objects, where each object may have custom properties of > several different datatypes and permission bits. > > The table fields that I have so far are a primary integer key (ID), text > representing the object's name, (NAME), and two fields "OWNER" and "PARENT" > which are integers representing other objects in this table. > > The problem I am running into is the object hierarchy and custom properties. > For example: If object #1 is a parent of object #2, and #1 has a property > named "location" then #2 should also have that property (although the value > and permissions may be different from the parent). > > I'm trying to see if I can do this some way I do not currently know how, > because the only thing I can think of is some delimited BLOB and recalculate > all the parent properties whenever the parent is changed which I imagine may > significently slow down my database.
The first thing to ask yourself here is whether or not it makes sense to use a database. Certainly that makes sense if you need concurrent read and write access, but if you only need to write from one source at a time an XML file sounds more like what you need. It supports your need for infinite hierarchy, and if you work without a DTD it allows setting of any properties that you would like. If you don't like the general bloat of an XML file you can make use of a library like libxml2 (http://www.xmlsoft.org) which natively and transparently supports compressed XML files. If you're absolutely sold on the need that this be in a database, buy a copy of Joe Selko's _SQL for Smarties_. It covers these hierarchical structures in great detail. Even after implementing this kind of structure before I wouldn't try it again without consulting Selko's book. Clay Dowling
