UNSAID drafted and mapped to SQL

In response to a thread on UNSAID in the comments list [1], I've
drafted a section on UNSAID [2]. Andy asked about implementing it on
an SQL-accessed triple store. I thought I'd share the answer with the
WG. I test for default negation by doing an outer join to the triple
in the positive and then constraining that part of that triple is
NULL:


CREATE TABLE holds (id INTEGER NOT NULL AUTO_INCREMENT,
                    s VARCHAR(80), p VARCHAR(80), o VARCHAR(80),
                    PRIMARY KEY(id));

-- _:a  foaf:name              "Alice" .
-- _:a  foaf:page              <http://work.example/alice> .
-- _:a  foaf:workplaceHomepage <http://work.example/alice> .
-- _:b  foaf:name              "Bob" .
-- _:c  foaf:name              "Eve" .
-- _:c  foaf:page              <http://isp.example/eve> .
-- _:c  foaf:workplaceHomepage <http://work.example/eve> .

INSERT INTO holds (s, p, o) VALUES ('_:a', 'foaf:name', '"Alice"');
INSERT INTO holds (s, p, o) VALUES ('_:a', 'foaf:page', '<http://work.example/alice>');
INSERT INTO holds (s, p, o) VALUES ('_:a', 'foaf:workplaceHomepage', '<http://work.example/alice>');
INSERT INTO holds (s, p, o) VALUES ('_:b', 'foaf:name', '"Bob"');
INSERT INTO holds (s, p, o) VALUES ('_:c', 'foaf:name', '"Eve"');
INSERT INTO holds (s, p, o) VALUES ('_:c', 'foaf:page', '<http://isp.example/eve>');
INSERT INTO holds (s, p, o) VALUES ('_:c', 'foaf:workplaceHomepage', '<http://work.example/eve>');

-- SELECT ?name
--  WHERE  ( ?x foaf:name  ?name )
--         UNSAID ( ?x  foaf:mbox  ?mbox ) 

SELECT h1.o AS name
  FROM holds AS h1
  LEFT OUTER JOIN holds AS h2 ON h2.s=h1.s AND h2.p="foaf:page"
 WHERE h1.p="foaf:name"
   AND h2.o IS NULL

-- +-------+
-- | name  |
-- +-------+
-- | "Bob" |
-- +-------+

-- SELECT ?name ?homepage
-- WHERE  ( ?x foaf:name  ?name )
--        OPTIONAL { ( ?x  foaf:page  ?homepage ) 
--            UNSAID ( ?x  foaf:workplaceHomepage  ?homepage ) }

SELECT h1.o AS name, h2.o AS homepage
  FROM holds AS h1
  LEFT OUTER JOIN holds AS h2 ON h2.s=h1.s AND h2.p="foaf:page"
  LEFT OUTER JOIN holds AS h3 ON h3.s=h1.s AND h3.p="foaf:workplaceHomepage" AND h2.o=h3.o
 WHERE h1.p="foaf:name"
   AND h3.o IS NULL

-- +-------+--------------------------+
-- | name  | homepage                 |
-- +-------+--------------------------+
-- | "Bob" | NULL                     |
-- | "Eve" | <http://isp.example/eve> |
-- +-------+--------------------------+


[1] http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2004Nov/thread.html#16
[2] http://www.w3.org/2001/sw/DataAccess/rq23/#unsaid
-- 
-eric

office: +81.466.49.1170 W3C, Keio Research Institute at SFC,
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