How to model data objects with multiple parents?

Question

How would I model the relationship between several objects, where one entity could be part of two separate, unrelated hierarchies, and each object could be connected with one or more other objects in a hierarchical order? I would like to do this in just 2 or 3 tables in the database.

Currently I have modeled it in two tables:

Entities
----------------------------------------------------------------
ID                          bigint        identity(1, 1)    PK
ParentID                    bigint        null              FK
Name                        varchar(100)  not null
Description                 varchar(256)  null

EntityRelationships
----------------------------------------------------------------
LEntityID                   bigint    not null    PK, FK
REntityID                   bigint    not null    PK, FK
EntityRelationshipTypeID    int       not null    PK, FK

Two columns: LEntityID and REntityID are the FKs in the Entities.ID column, and ParentID is the FK in the ID column. This model is likely to work fine if the object never has more than one parent. I need to be able to allow entities to have more than one parent.

The natural keys on the tables are:

Entities: ParentID, Name
EntityRelationships: LEntityID, REntityID, EntityRelationshipTypeID

, .

.

Answer 1

, . EntityParentRelation

EntityParentRelation
--------------------------------------------------------------------------------
ID                           bigint                  identity(1,1)   pk   
EntityID                     bigint                  not null        fk
ParentID                     bigint                  not null        fk

EntityID ParentID fks Entities.ID. ParentID Entities. EntityRelationships

fk Entities, fk EntityParentRelation.ID LEntityID REntittyID.

, :).