In The Below Example i Expand that how to Develop Sales Order Report in Extension 2.0 how to use multiple data item 
and how to use Dataitem Property in extension 2.0

report 50110 CustomSalesOrder { DefaultLayout = RDLC; RDLCLayout = 'CustomSalesOrder.rdl'; dataset { // This is Sales Header DataItem dataitem("Sales Header";"Sales Header") { DataItemTableView=WHERE("Document Type"=CONST(Order)); PrintOnlyIfDetail=true; RequestFilterFields="No.", "Sell-to Customer No.","Posting Date"; column(Sell_to_Customer_No_;"Sell-to Customer No.") { } column(CompanyName;CompanyName) { } // This is Sales Line DataItem dataitem("Sales Line";"Sales Line") { // DataItem Properties DataItemLinkReference="Sales Header"; DataItemTableView=sorting("Document Type","Document No.","Line No.") order(ascending); PrintOnlyIfDetail= false; DataItemLink = "Document Type"=FIELD("Document Type"),"Document No."=FIELD("No."); // Adding Column from Sales Line Dataitem column(Quantity;Quantity) { } column(No_;"No.") { } // Sales Line DataItem Triggers trigger OnAfterGetRecord() begin if "Sales Line".Quantity = 0 then UnitePriceToPrint:=0 else UnitePriceToPrint:=Round("Sales Line"."Line Amount" / "Sales Line".Quantity,0.00001); AllTotalAmount:=UnitePriceToPrint + UnitePriceToPrint; PaymentNewDescription:=PaymentTerms.Description; end; } // This is DataItem 1 Sales Header Triggers; trigger OnPreDataItem() begin PaymentNewDescription:=PaymentTerms.Description; CompanyName:=CompanyInfo.Name; end; } } trigger OnPreReport() begin CompanyInfo.Get(); end; // All the Global Variable are here var CompanyInfo:Record "Company Information"; UnitePriceToPrint :Decimal; CompanyName:Text [50]; }