state writing tag {
	    tid  INTEGER  NOT NULL  PRIMARY KEY AUTOINCREMENT,
	    fid  INTEGER  NOT NULL  REFERENCES file,     -- File the item belongs to
	    lod  INTEGER            REFERENCES symbol,   -- Line of development (NULL => Trunk)
	    sid  INTEGER  NOT NULL  REFERENCES symbol,   -- Symbol capturing the tag

	    rev  INTEGER  NOT NULL  REFERENCES revision  -- The revision being tagged.
	}
	} { rev sid }
	# Indices on: rev (revision successors)
	#             sid (tag predecessors, branch successors/predecessors)

	state writing branch {
	    bid   INTEGER  NOT NULL  PRIMARY KEY AUTOINCREMENT,
	    fid   INTEGER  NOT NULL  REFERENCES file,     -- File the item belongs to
	    lod   INTEGER            REFERENCES symbol,   -- Line of development (NULL => Trunk)
	    sid   INTEGER  NOT NULL  REFERENCES symbol,   -- Symbol capturing the branch

	    root  INTEGER            REFERENCES revision, -- Revision the branch sprouts from
	    first INTEGER            REFERENCES revision, -- First revision committed to the branch
	    bra   TEXT     NOT NULL,                      -- branch number
	    pos   INTEGER  NOT NULL                       -- creation order in root.

	    -- A branch can exist without root. It happens when the
            -- only revision on trunk is the unnecessary dead one the
            -- branch was sprouted from and it has commits. The branch
            -- will exist to be the LOD of its revisions, nothing to
            -- sprout from, the dead revision was removed, hence no
            -- root.
	}
	} { root first sid }
	# Indices on: root  (revision successors)
	#             first (revision predecessors)
	#             sid   (tag predecessors, branch successors/predecessors)

	# Project level ...
	#	pLineOfDevelopment, pSymbol, pBranch, pTag, pTrunk
	#
	#	pTrunk  <- pLineOfDevelopment
	#	pBranch <- pSymbol, pLineOfDevelopment
	#	pTag    <- pSymbol, pLineOfDevelopment