Retrieving Metadata - Working with Schema Rowsets

When you need more metadata than is available in the ADOMD.NET object model, ADOMD.NET provides the capability to retrieve the full range of XML for Analysis (XMLA), OLE DB, OLE DB for OLAP, and OLE DB for Data Mining schema rowsets:

XML for Analysis metadata
The XML for Analysis schema rowsets provide a method for retrieving low-level information about the server. Information available includes the data sources available on the server, the keywords reserved by the provider, the literals supported by the provider, and more. You can even use an XML for Analysis schema rowset to discover all schema rowsets supported by the provider.

OLE DB metadata
The OLE DB schema rowsets provide an industry-standard method for retrieving information from a variety of providers.

OLAP metadata
Schema information provided for an analytical data source includes databases or catalogs available from the analytical data source, cubes and mining models in a database, roles that exist for cubes at the data source, and more.

Data Mining metadata
In addition to OLAP metadata, data mining metadata can be retrieved using schema rowsets. The available rowsets expose information on the available data mining models in the database, the available mining algorithms, the parameters that the algorithm require, mining structures, and more.

For each of these various schema rowsets, you retrieve metadata from the rowset by passing either a GUID or XMLA name with the GetSchemaDataSet method of the AdomdConnection object.

Retrieving Metadata by Passing GUIDS

The AdomdSchemaGuid class contains a list of fields that represent the schema rowsets most commonly supported by providers and analytical data sources. To retrieve both general and provider-specific metadata from a provider or analytical data source, you use the GUIDs contained within the AdomdSchemaGuid object with the either of the following methods:

• GetSchemaDataSet

• GetSchemaDataSet

Retrieving Metadata by Passing XMLA Names

The following methods take as arguments the XMLA schema name that identifies which schema information to return, and an array of restrictions on those returned columns:

• GetSchemaDataSet

• GetSchemaDataSet

• GetSchemaDataSet

• GetSchemaDataSet

Each of these methods returns an instance of a DataSet object that is populated with the schema information. The DataSet object is from the System.Data namespace of the Microsoft .NET Framework Class Library.

Example

In the following example, the GetActions function takes a connection, the cube name, a coordinate, and a coordinate type, retrieves an MDSCHEMA_ACTIONS Rowset, and returns the actions available on the selected coordinate.

//The following function can be called with the following data:
//ae.GetActions(conn, "Adventure Works","[Geography].[City]",6 );

//This would return a DataSet containing the actions available for cells
//in the Adventure Works cube on [Geography].[City].
private System.Data.DataSet GetActions(AdomdConnection Connection, string Cube, string Coordinate, int CoordinateType)
{
    //Create a restriction collection to restrict the schema information to be returned.
    AdomdRestrictionCollection restrictions= new AdomdRestrictionCollection();
    restrictions.Add("CUBE_NAME", Cube);
    restrictions.Add("COORDINATE", Coordinate);
    restrictions.Add("COORDINATE_TYPE", CoordinateType); //6 = Cell coordinate

    //Open and return a schema rowset, given the correct restictions
    return Connection.GetSchemaDataSet("MDSCHEMA_ACTIONS", restrictions);
}