Retrieves TopologyEntities from the database. TopologyEntities are views on OnmsEntities (such as OnmsNode, CdpLink, etc.)
which are reduced to the needs of displaying a toplogy:
- they are derived from one OnmsEntity / a database table
- they contain only the relevant subset of attributes of their OnmsEntity
- relations are just referenced by a primitive key such as a String or Integer instead of (lazy loaded) object references
The above features allow for fast database retrieval.