1. A computer-implemented method for indexing and searching entity-relationship data performed by a computerized device having a processor, comprising: providing a database of entity-relationship data which includes identifiers of entities and indications of relationships between the entities, indicating which entities are related to each other; representing the entities of the provided database as respective documents, each document containing content and metadata of a respective entity; representing the entities of the provided database as respective categories; representing each relationship instance, which indicates a relationship between a plurality of entities, in the database, as a category set that contains categories of all participating entities in the relationship; and indexing the entity-relationship data of a populated logical document model as an inverted index, which indicates for each relationship attribute, the entities to which it relates, allowing lookup in the inverted index of results of queries based on relationship participation patterns.