Object-Relational Mapping question

waitinforatrain

Hi,

I'm trying to do up an ORM structure for a Java project I'm doing. I was just using Objects and HashMaps up until now but it's getting far too complicated for that.

The software basically has a directed graph structure (i.e. http://en.wikipedia.org/wiki/Graph_%28data_structure%29 ) that the user can draw, and stores properties about each 'node' in the graph.

Let's say there's 3 types of nodes, NodeType1, NodeType2, NodeType3. They all have different properties associated with them.

So the graph structure looks like this:

Node

ID   ParentsID  Name
1    2          Node 1
2    3          Node 2
etc...

(ParentsID is one-to-many, keeps track of the parents of each node on the digraph)

Parent

ID   NodeID
2     2
2     3
etc...

Now, as per this article http://www.objectmatter.com/vbsf/docs/maptool/ormapping.html I can deal with the different node types by one-to-one mapping of NodeTypeX to a Node ID, e.g.

NodeType 1

ID    NodeID   Value1    Value2

That's all fine. Here's where it gets a bit tricky:

Some of the NodeTypes store values for each parent of that node, so I need to link them to a separate table with that e.g.


NodeType 2

ID    NodeID   Value1    ParentValuesID

ParentValue

ID     NodeID     Value

My problem here is that the ParentValue table would have to be synchronised with the Parent table, as each parent of the node would need a value. When a parent to a node is added or removed I need it to change both the Parent and ParentValue tables.

What's standard practice for this situation? Can this be handled automatically by Hibernate/JPA etc? Will they have to be synchronised manually?



Part 2

It gets more complicated. The software is for Bayesian networks.

One type of node stores a Conditional Probability Table a bit like this (the table at the bottom):



So this node needs to store a table of arbitrary length (the states aren't limited to false/true). Is this possible with a relational database?

This is all I have so far
ObservedNode

ID     NodeID     StatesID (one-to-many)

State

ID    Name

Then come up with some way of permutating these into one table with support for redundant states.

I have no idea where to begin with this. Any help appreciated.

ronivek

Are you being restricted to using a relational database? If not I'd suggest you do a little research into graph databases; as you seem to be using Java then neo4j would be an option.

waitinforatrain

I'm not restricted to relational databases. Thanks for the link, I'd never have found that on my own!

Edit: Having looked through it, this won't do what I need either as it has no way to store a variable length CPT either... any other suggestions welcome

peterneubauer

Hi there,
you could store the CPT either are a number of properties on the Node by encoding every tuple into a key-value pair, or actually serialize the CPT in some format into a ByteArray that you can store as a "CPT=xxxx" property. That doesn't require any structure or fixed/constant length ...
http://api.neo4j.org/current/org/neo4j/api/core/PropertyContainer.html#setProperty(java.lang.String, java.lang.Object)