Microsoft SQL Server spatial databases do not have built-in OGC compliant metadata tables. If the Maintain OGC metadata option is checked GISquirrel will automatically create and manage the contents of the OGC standard metadata table geometry_columns in Microsoft SQL Server databases. PostgreSQL/PostGIS databases have their own, built-in, OGC-compliant geometry_columns view, which is automatically maintained by PostGIS and cannot be written to.
The geometry_columns table is created when GISquirrel creates its own metadata tables and updated whenever GISquirrel's metadata are updated. There is a conceptual and structural difference between GISquirrel and OGC metadata. GISquirrel is based on the concept of feature classes. Any number of feature classes can be based on the same database table and each row in the main GISquirrel metadata table represents a feature class. The OGC geometry_columns table, on the other hand, has one row per spatial table or view. Thus, if multiple GISquirrel feature classes are based on the same table, only one row can be added to the geometry_columns table and that row will be removed when the last GISquirrel feature class based on the table is deleted.
The purpose of this option is enhanced interoperability, particularly with the popular open source desktop GIS programme, Quantum GIS (QGIS). Having a geometry_column metadata table can dramatically speed up browsing of large SQL Server databases, which can otherwise take can take a very long time with QGIS.