Property chains are rules written like this:
R <- S o T
Here the 'o' is the composition operator. This means that an 'S' edge followed by a 'T' edge implies an R edge spanning both.
In rule-oriented terms:
IF x S y AND y T z THEN x R z
Note the converse is not implied.
Property Chains in RO
RO makes frequent use of property chains. See ROGuide for more details