You can override the default merging process by creating virtual objects when you design the virtual cube. You can create these virtual objects either to hide or to rename objects from the two cubes.
For example, assume you want to merge two dimensions, Sales and GlobalSales, from two cubes. You can create two virtual dimensions in the virtual cube (one for each of the dimensions that you want to merge) and name both of these virtual dimensions AllSales. When the two cubes are merged, the virtual cube will have a virtual dimension called AllSales, which contains the data from both dimensions. You can do the same thing for virtual measures and virtual members.
However, because levels cannot be renamed in the virtual cube, levels from the hierarchies of the two cubes are not merged in the same way as measures and members.
When two dimensions are merged at runtime, the merging process iterates through all the levels of the two dimensions starting at level zero and checks if the level names are identical. If they are identical, the merged virtual level will have the same name as the levels in both cubes. If the level names at the same depth differ in the two cubes, the virtual level will be named by concatenating the two level names. Although the levels at the same depth of the two hierarchies can have different names, they must refer to the same things. If they do not refer to the same things, their merging will be meaningless.
If the hierarchy of one dimension contains more levels than the hierarchy of the other dimension, the levels that exist in only the first hierarchy will be added to the virtual dimension following the merged levels.
Suppose that you have two cubes, EastSales and WestSales, that are merged to create a virtual cube AllSales. EastSales has a dimension called Geography with hierarchy levels Country, State, City, and Neighborhood. WestSales also has a dimension called Geography with hierarchy levels Country, Province, and City. When they are merged, the AllSales cube will have a dimension called Geography with hierarchy levels as Country, State Province, City, and Neighborhood. Because all of the four levels in the virtual cube are valid, the merging of the two dimensions is successful.
However, if the Geography dimension of WestSales cube has a hierarchy with levels Country, City, and Neighborhood. When the EastSales and WestSales are merged, the Geography dimension of the AllSales cube will have hierarchy levels as Country, State City, City Neighborhood, and Neighborhood. Because the merged levels like State City, and City Neighborhood are not valid, the merging of two dimensions is not useful.
To avoid name conflicts, calculated measures or calculated members from the two dependent cubes are not propagated to the virtual cube. To use calculated measures or members from the two cubes in the virtual cube, you need to explicitly define the equivalent calculated measures or members in the virtual cube.
When you delete a virtual cube, all the elements that are associated with this virtual cube, including the virtual dimensions, virtual measures, virtual members and MDX calculated measures, are also deleted.