Re: Nested Sets vs. Nested Intervals

amado.alves_at_netcabo.pt schrieb:
> In the Dot language (Graphviz from AT&T):
>
> digraph {
> Employees -> x1
> Employees -> x2
> Employees -> x3
> Name -> x4
> Name -> x5
> Name -> x6
> Dept -> x7
> Dept -> x8
> Dept -> x9
> Salary -> x10
> Salary -> x11
> Salary -> x12
> Departments -> x13
> Departments -> x14
> Deptno -> x15
> Deptno -> x16
> Name -> x17
> Name -> x18
> x1 -> x4 -> Smith
> x1 -> x7 -> x13
> x1 -> x10 -> 1000
> x2 -> x5 -> Scott
> x2 -> x8 -> x14
> x2 -> x11 -> 2000
> x3 -> x6 -> King
> x3 -> x9 -> x14
> x3 -> x12 -> 3000
> x13 -> x15 -> 1
> x13 -> x17 -> Accounting
> x14 -> x16 -> 2
> x14 -> x18 -> Manufacturing
> }
>
> Note this is a canonical, literal translation of the given relational
> database. Modelling the semantic domain directly on Mneson would
> simplify things. For example the Deptno is probably not necessary
> semantically but just a requirement of the relational model for a key,
> or for the connection (join), or both. Mneson does not need keys. A
> distinct entity is a distinct vertex. Connected entities simply share a
> topology.

Assume we have an arbitrary graph. Are there any rules for determining the role of its nodes such as collection (Employess, Departments), instance ('John Smith', 'Accounting Department'), properties (age, salary) etc?

Can these roles be mixed, for example, a node could play a role of property with respect to one subgraph and an entity for another subgraph?

Is it true that this database engine does not know anything about the roles of nodes and manipulates only the graph using some formalism?

Is there any informal interpretation of x -> y connection which would allow me to build a graph given some problem domain description?

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