2.1.1837 Part 4 Section 19.2.2.24, rel (Diagram Relationship)

a.   The standard places no restrictions on the kind of shape that is defined by the idcntr attribute.

Office requires that this shape be a connector.

b.   The standard does not explicitly state that the shape identified by the idcntr attribute must exist.

Office requires the shape identified by the idcntr attribute to exist.

c.   The standard does not explicitly state that the shape identified by the idsrc attribute must exist.

Office requires the shape identified by the idsrc attribute to exist.

d.   The standard does not explicitly state that the shape identified by the iddest attribute must exist.

Office requires the shape identified by the iddest attribute must exist.

e.   The standard indicates that the idsrc, iddest and idcntr attributes are specified as a string.

Office requires these attributes use a reference to an object ID in the form of an object name, as described in the ST_ObjIDRef (§3.9.4, ST_ObjIDRef) simple type.