[[File:UDOM_PlantPartRelations.png|thumb|220px|alt=Relations of plant parts|Possible relations between parts of plant]]
An important aspect of the datamodel has not been discussed yet, namely <b>how are the blocks (=MetaClasses) related to each other?</b>
==Entity Relationship Model (ER model)==
[[File:UDOM_Relating4.png|thumb|400 220 px|alt=ER-model|Entitiy-Relationship-Model]]In software engineering, such an abstract descriptive model is called Entity–Relationship model (ER model) and describes the entities (={{UBIK}} metaclassesMetaClasses) and relationships between them. Usually this information is depicted in an entitiyentity-relationship-diagram (ERD), which draws the corresponding data objects and relations as rectangles and lines between them, respectively. The metaclass MetaClass ''„CONTROL“'' can be drawn as diamond, signalling the additional block between these two metaclassesMetaClasses, which is always needed for each relation of cardinality n : n.
==About References and Relations==
[[File:UDOM_Relating5_RefRel.png|thumb|400 220 px|alt=References and Relations|{{UBIK}} References and Relations]]Concluding and summarizing the above discussion we finally depict the two possible types of relation in the {{UBIK}} metamodelMetaModel.
{{UMM|
Congratulations, we integrated another important issue in our data- and object model:
{{Checked}} <b>Relationships between blocks (metaclassesMetaClasses)</b>