Object Exchange Model

The Object Exchange Model ( OEM) has become the de facto standard for storing semi-structured data durchgesetzt1 "Originally it was for the TSIMMIS ( The Stanford - IBM Manager of Multiple Information Sources ) project develops. "

The OEM model is based on the concept of a directed graph. " A ( directed) graph is a pair G = (V, E), in this case V is a finite set of nodes and EVV a relation on V, the set of edges. " 2 However, there are within an OEM model also leaves Va, of which can lead away from any edges.

The nodes of an OEM graph represent the actual objects that have a unique ID. Inside a OEM model Vc and Va atomic objects, a distinction between complex objects. The attributes of complex objects are described only by the edges, which in turn refer to complex objects or atomic objects. In addition, the graph contains one or more roots r1 to rk from which all objects must be reachable. The atomic objects represent the leaves of the graph, ie it can only lead an edge to them, but no lead away. The atomic objects contain the values ​​of complex objects m, where they are associated with the type integer, string, image or ähnliches.3

" Formally, semi-structured data can thus as G = ( V, E, r1, ..., rk, v) define:

V = Vc Va: the set of nodes, wherein the set of complex objects Vc and Va is the amount of atomic objects;

Vc E AV the set of edges, where A is the set of attributes;

Ri the set of roots;

V: Va D a figure objects atomic values ​​of D, the amount of all the atomic values ​​assigns " 4.

All possible edges of the graph are generally defined by the Cartesian product V Vc. This indicates that all complex objects can be referenced by all objects. However, atomic objects can have no reference to complex objects.

Greiner has this Cartesian product ( the set of all attributes) expanded by a factor of A: vc V. This expresses that the subset of edges can be assigned to each attribute cheap. Thus, the elements of the subset of the edge E is also associated with an attribute; the set of attributes is not explicitly included in the basic set G of graphs.

The same is true with the set of all possible values ​​of D that are associated with the atomic objects with the picture Va D.

The abbreviations of the graph are in principle also to the set of complex objects. The roots must satisfy the condition that they all nodes can be referenced. To show an example of a graph having two roots, the root can be omitted in Figure 1:

Thus, & 2 and & 3 roots.

1) 2) 3) 4)