c# - Oracle Schema Restrictions -

i want oracle restrictions have in sql server //https://msdn.microsoft.com/en-us/library/ms136366(v=vs.110).aspx/ below method taking time in retrieving data

    public override ienumerable<icolumninformation> gettablecolumnlist(itableinformation table)     {         var result = new list<icolumninformation>();          // if table flagged excluded bail empty list         if (table.exclude)         {             return result;         }          var strb = new oracleclient.oracleconnectionstringbuilder(this.connectionstring);         datatable columns;         using (var connection = new oracleclient.oracleconnection(connectionstring))         {             // connect database retrieve schema information.             connection.open();             columns = connection.getschema("columns");             if (columns != null && columns.rows.count > 0)             {                 columns.asenumerable().tolist()                     .foreach(t => result.add(new columninformation(                         t.field<string>("column_name"),                         t.isnull("length") ? 0 : t.field<int>("length"),                         null,                          t.field<string>("owner"),                         false,                          table)));                 }         }         return result;     } public columninformation(string name, int length, type type, string databasetype, bool exclude = false, itableinformation parent = null)         {             this.name = name;             this.length = length;             this.type = type;             this.dbtype = databasetype;             this.exclude = exclude;             this.parent = parent;           } 

where :columninformation class has constructor.

i have following questions getting columns details table in oracle:

1. do have schema restrictions in oracle sql server?
2. that linq giving me error of type specfications.
3. data table getting data in more 5 minutes.

. help!!