There are three elements in the table:
SymmetryName: The name of the symmetry definition that this pairing belongs to.
GroupName: The group this label belongs to
ConnectedSymmetry: The label in the CMLElement definition of the structure (the name is found in SymmetryDefinition).
AtomId: The corresponding atom id (within the corresponding CMLStructure.
The collection of entries with the same SymmetryName represent the a particular symmetry assignment.
The types of connected symmetries (ConnectedSymmetry) are:
X: No symmetry requirement
L: The group has to be linear (see LinearDefinition).
a number: The group has to have the secondary symmetry of this number.
N:The rest of the complete symmetry definition is in SymmetryDefinition.
The symmetry element ExternalSymmetry-C(B1)(B1)(B2)B2) represents a carbon atom with two types of equivalent groups attached, B1 and B2. To represent this element, there are four elements in the SymmetryPairAssignments table. All have the same SymmetryName, ExternalSymmetry-C(B1)(B1)(B2)B2) (the table query searches for this name to find all the elements:
SELECT GroupName, AtomId, ConnectedSymmetry
FROM SymmetryPairAssignments
WHERE SymmetryName="ExternalSymmetry-C(B1)(B1)(B2)B2)";
The result of the query is the following table:
GroupName AtomdId ConnectedSymmetry
Group0 a2 X
Group0 a3 X
Group1 a4 X
Group1 a5 X
The AtomId correspond to the CMLStructure assigned within the SymmetryDefinition table element named ExternalSymmetry-C(B1)(B1)(B2)B2). In this table there are two groups defined: Group0 and Group1, This means that a2 and a3 have to be the same and that a4 and a5 have to be the same. But a2 and a3 have to be different from a4 and a5. Atoms a2, a3, a4 and a5 correspond to the four atoms around the CarbonAtom. The name CarbonAtom was specified in the SymmetryDefinition table. The structure is defined in CMLStructures:
CREATE TABLE `SymmetryPairAssignments` (
`SymmetryName` varchar(40) DEFAULT NULL,
`GroupName` varchar(20) DEFAULT NULL,
`AtomId` varchar(20) DEFAULT NULL,
`ConnectedSymmetry` varchar(10) DEFAULT 'N'
) ENGINE=MyISAM DEFAULT CHARSET=latin1;