Entity-Relationship Diagrams: Identifying which way a relationship flows I am having trouble grasping the "relationship" concept of an entity-relationship diagram. For example, you have Classroom and Furniture as your entities. If you were to put a relationship diamond with the word Contains and a line between the two, how would one be able to tell which contains which? 

Obviously we know that Furniture cannot contain a Classroom, however, when it comes to applications and data models there are often foreign concepts and terms meaning we have no prior knowledge of the relationship or possibilities.

Without actually having words to describe the diagram, which would defeat the purpose of the ERD (as it should speak for itself), how would one determine visually which way the relationship was flowing?

Thanks in advance.

FYI; in case it is relevant - the line touching Classroom has a "one and only one" symbol, the line touching Furniture has a "zero through many" symbol.
The flow of ERD relationships go in both directions. Cardinality expresses the rules governing the relationships between entities.  The 'one and only one' of classroom provides you with a verbal logic of - 'A classroom must contain..'.  The 'zero to many' furniture cardinality provides 'zero to many pieces of furniture.'  

Don't think of the furniture physically being in the classroom, just that a connection exists between the two.