jena rules how to infer "object properties"

Hi, could you help me on a problem i still stuck on ?

I've got an FOAF ontology merged with another one : photography.
People are linked with a "figureOnImage" object property and I want to infere that they know (FOAF:Knows : object Property) each other.

1 - question :
With the rules files :
@prefix foaf: <http://xmlns.com/foaf/0.1/knows#>. (or @prefix foaf: <http://xmlns.com/foaf/0.1#>.) same
@prefix exif: <http://www.w3.org/2003/12/exif/ns#>.
@prefix photo: <http://www.photographyontology.org.uk/ontologies/photography/photography.owl#>.
[rule1: (?f photo:figureOnImage ?a) (?g photo:figureOnImage ?a) -> (?f foaf:knows ?g) (?g foaf:knows ?f)]
[cid:image003.png [ at ] 01CF5B0A.35151B50]
Result seems to be correct except that each people knows himself (not wrong ;o) ) but I would understand it with a rule like :
[rule1: (?f photo:figureOnImage ?a) (?g photo:figureOnImage ?a) -> (?f foaf:knows ?f) ]

What's wrong with my rules ?

2 - question : I try to link two persons with an "FOAF:knows" object property and not with an annotation. How can I infer and use object properties ?

Thanks

Regards

Wilfrid Tourigny

Screenshots for question 1 :

[cid:image005.jpg [ at ] 01CF5B0D.6B699DE0]

[cid:image006.jpg [ at ] 01CF5B0D.6B699DE0]
Result expected in Question 2 :[cid:image004.png [ at ] 01CF5B0B.F07CEAC0]